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Freshwater parameters in the state of Rio Grande do Sul, southern Brazil, and their influence on fish distribution and aquaculture

ABSTRACT

This study analyzed the relationship between several water quality parameters (pH, hardness, alkalinity, turbidity, iron and manganese) levels measured over a 16 year period with fish distribution and aquaculture in the state of Rio Grande do Sul, Southern Brazil. The mean pH values were within a neutral range (6.5-7.5), but the maximum and minimum values reached inappropriate levels for fish farming in some cities. Alkalinity levels were very low (except in the southwest region of the state), which may have contributed to pH variation. Hardness, turbidity, iron (except the region near Caçapava do Sul City) and manganese were within safe ranges for fish farming; however, turbidity levels occasionally increased to levels outside the safe range. In conclusion, the water quality in the Rio Grande do Sul, in general, can be considered adequate for aquaculture, but the fish farmers must be aware of the methods to reduce turbidity, such as the use of calcium sulfate.

Keywords:
Alkalinity; Hardness; Iron; pH; Turbidity

RESUMO

Este estudo analisou a relação entre vários parâmetros de qualidade da água (pH, dureza, alcalinidade, turbidez, ferro e manganês durante 16 anos) com a distribuição de peixes e piscicultura no estado do Rio Grande do Sul, Brasil. O pH ficou em média em uma faixa neutra (6,5-7,5), mas valores máximos e mínimos atingiram níveis não apropriados para a piscicultura em algumas cidades. Os valores de alcalinidade foram baixos (exceto na região sudoeste do estado), o que poderia contribuir para oscilações no pH. Dureza, turbidez, ferro (exceto na região próxima à cidade de Caçapava do Sul) e manganês ficaram dentro de níveis aceitáveis para a piscicultura, mas a turbidez ocasionalmente elevou-se a níveis fora dessa faixa aceitável e os piscicultores devem ter algum mecanismo para reduzi-los. Em conclusão, de forma geral a qualidade da água do Rio Grande do Sul pode ser considerada adequada para a aquicultura, mas os piscicultores devem conhecer métodos para corrigir a turbidez, como a utilização de sulfato de cálcio.

Introduction

Knowledge of the ideal range of water quality parameters is a crucial factor in aquaculture (Copatti et al., 2005Copatti, C. E., I. J. Coldebella, J. Radünz Neto, L. O. Garcia, M. C. Rocha & B. Baldisserotto. 2005. Effect of dietary calcium on growth and survival of silver catfish juveniles, Rhamdia quelen (Heptapteridae), exposed to different water pH. Aquaculture Nutrition, 11: 345-350.). Monitoring water quality is very important because it influences fish metabolism, reproduction, feeding and growth. Some important parameters to be considered in a long-term analysis on the effects on aquaculture are pH, hardness, alkalinity and turbidity (Zweig et al., 1999Zweig, R. D., J. D. Morton & M. M. Stewart. 1999. Source water quality for aquaculture. Washington, World Bank, 62 p.; Kristensen et al., 2009Kristensen, T., A. Atland, T. Rosten, H. A. Urke & B. O. Rosseland. 2009. Important influent-water quality parameters at freshwater production sites in two salmon producing countries. Aquacultural Engineering, 41: 53-59.; Baldisserotto, 2011Baldisserotto, B. 2011.Water pH and hardness affect growth of freshwater teleosts. Revista Brasileira de Zootecnia, 40: 138-144.).

The recommended pH range for fish is 6.5 to 9.0 (Baldisserotto, 2011Baldisserotto, B. 2011.Water pH and hardness affect growth of freshwater teleosts. Revista Brasileira de Zootecnia, 40: 138-144.). Water hardness is the concentration of all divalent cations in water, and calcium (Ca2+) and magnesium (Mg2+) are the most common cations in almost all freshwater systems. The recommended water hardness range for raising North American fishes is 20-400 mg CaCO3 L-1 (Boyd & Tucker, 1998Boyd, C. E. & C. S. Tucker. 1998. Pond aquaculture water quality management. Norwell, Kluwer Academic Publishers, 700 p.; Zweig et al., 1999Zweig, R. D., J. D. Morton & M. M. Stewart. 1999. Source water quality for aquaculture. Washington, World Bank, 62 p.), but a recent review indicated that high water hardness is needed only for species that are found in hard water in the environment (Baldisserotto, 2011Baldisserotto, B. 2011.Water pH and hardness affect growth of freshwater teleosts. Revista Brasileira de Zootecnia, 40: 138-144.).

Alkalinity of the water is the ability to accept protons or to neutralize acids, and bicarbonate, carbonate and hydroxide are considered the predominant bases in natural waters. The alkalinity level recommended for growing fish should be above 20 mg L-1 (Boyd, 2000Boyd, C. E. 2000. Water quality: an introduction. Norwell, Kluwer Academic Publishers, 330 p.). Turbidity is a measure of the light scattering properties of water and is related to transparency. It may be due to colloidal clay particles from the run-off of pond dikes or river shores that contains clay (Yi et al., 2003Yi, Y., C. K. Lin & J. S. Diana. 2003. Techniques to mitigate clay turbidity problems in fertilized earthen fish ponds. Aquacultural Engineering, 27: 39-51.; Rocha et al., 2015Rocha, F. C., E. M. Andrade & F. B. Lopes. 2015. Water quality index calculated from biological, physical and chemical attributes. Environmental Monitoring and Assessment, 187: 4163.), or to the presence of phytoplankton (Crossetti et al., 2014Crossetti, L. O., F. Schneck, L. M. Freitas-Teixeira & D. Motta-Marques. 2014. The influence of environmental variables on spatial and temporal phytoplankton dissimilarity in a large shallow subtropical lake (lake Mangueira, southern Brazil). Acta Limnologica Brasiliensia, 26: 111-118.).

In addition to these more common water parameters, the analysis of some waterborne metals can also be important for fish farming. In southern Brazil the soil is very rich in iron (Fe) and also contains manganese (Mn) (Brasil, 1973Brasil. 1973. Levantamento de reconhecimento dos solos do estado do Rio Grande do Sul. Boletim Técnico n° 30. Recife, Ministério da Agricultura, 431 p.), and consequently their water levels are high (Kochhann et al., 2013Kochhann, D., E. R. Behr, A. Chaves, M. F. Mesko, V. L. Dressler, E. M. M. Flores & B. Baldisserotto. 2013. Environmental quality evaluation of the Vacacaí River, Rio Grande do Sul, Brazil. Environmental Earth Sciences, 70: 1727-1733.). While iron is a vital micronutrient for teleost fish, as it is an integral component of proteins involved in cellular respiration and oxygen transfer, it is toxic in excess (Bury et al., 2003Bury, N. R., P. A. Walker & C. N. Glover. 2003. Nutritive metal uptake by teleost fish. The Journal of Experimental Biology, 206: 11-23.). Manganese is a cofactor of a number of enzymes such as superoxide dismutase and those involved in glucose oxidation, metabolism of fatty acids and amino acids (Satoh et al., 2001Satoh, S., M. J. Apines, T. Tsukioka, V. Kiron, T. Watanabe & S. Fujita. 2001. Bioavailability of amino acid-chelated and glass-embedded manganese to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings. Aquaculture Research, 32: 18-25.) and presents a very low toxicity risk for fish (Dolci et al., 2013Dolci, G. S., V. T. Dias, K. Roversi, Kr. Roversi, C. S. Pase, H. J. Segat, A. M. Teixeira, D. M. Benvegnú, F. Trevizol, R. C. S. Barcelos, A. P. K. Riffel, M. A. G. Nunes, V. L. Dressler, E. M. M. Flores, B. Baldisserotto & M. E. Bürger. 2013. Moderate hypoxia is able to minimize the manganese-induced toxicity in tissues of silver catfish (Rhamdia quelen ). Ecotoxicology and Environmental Safety, 91: 103-109.).

Due to economic restraints or lack of knowledge of the best water quality ranges for a given species, fish farmers usually accept general water quality parameters (Colt et al., 2006Colt, J. 2006. Water quality requirements for reuse systems. Aquacultural Engineering, 34: 143-156.). In southern Brazil, where most fish farmers are small-scale producers, there is almost no analysis, knowledge or control of water quality parameters (Cardoso et al., 2009Cardoso E. S., H. M. O. Rocha & M. C. Furlan. 2009. A piscicultura no município de Santa Maria, RS. Ciência e Natura, 31: 131-140.). Therefore, the objective of this study was to analyze water quality parameters (pH, alkalinity, hardness, turbidity, Fe and Mn levels) in continental waters this state, in the last 16 years, relating these data with their use in fish distribution and aquaculture. The knowledge of the variation range of these parameters is important to allow fish farmers to avoid or reduce problems due to water quality parameters in their culture.

Materials and Methods

Mean monthly water quality parameters were provided by the Companhia Riograndense de Saneamento (CORSAN), which measures daily water quality in its water treatment stations (WTS) in the state of Rio Grande do Sul, Brazil. Data were collected from the WTS located in various cities of this state (Alegrete, Alvorada, Bento Gonçalves, Caçapava do Sul, Cachoeirinha, Cachoeira do Sul, Camaquã, Cidreira, Cruz Alta, Carazinho, Frederico Westphalen, Gaurama, Lagoa Vermelha, Palmeira das Missões, Passo Fundo, Quaraí, São Borja, Santa Maria, Santiago, São Marcos, Santa Rosa, Três Passos, Taquara, Torres and Uruguaiana) over 16 years (1996-2011) except water hardness, which was analyzed from 1996 to 2003.

The pH, hardness, alkalinity, Fe and Mn levels were measured by titrimetric methods described by APHA (2005American Public Health Association (APHA), American Water Works Association & Water Environment Federation. 2005. Standard methods for the examination of water and wastewater. Eaton, A. D. & M. A. H. Franson (Eds.). 21st ed. Washington, D. C., American Public Health Association.). Turbidity was determined with a turbidimeter (HACH 2100 P). Maps of the water quality parameters analyzed were produced with the software Spring 4.3.3 (Câmara et al., 1996Câmara, G., R. C. M. Souza, U. M. Freitas & J. Garrido. 1996. Spring: integrating remote sensing and GIS by object-oriented data modelling. Computers & Graphics, 20: 395-403.), which related the geographic location of the cities to each parameter's overall mean, minimum and maximum values.

Results

Mean water pH in Rio Grande do Sul was 6.5-7.5 (Fig. 1A). Minimum (Fig. 1B) and maximum pH values (Fig. 1C) occurred in the cities of Rio Grande (in the south of the state) (pH 4.3), Alvorada and Cachoeirinha (in the east of the state) (pH 9.5). The mean water hardness range was 18-30 mg CaCO3 L-1. The lowest mean hardness value was measured in the city of Santiago (in the center of the state) (10 mg CaCO3 L-1) (Fig. 2A). The city of Cidreira (in the east of the state) showed the highest mean value (120 mg CaCO3 L-1), but other high values (48-53 mg CaCO3 L-1) and low values (30-36 mg CaCO3 L-1) were observed in the southwest of the state (Figs. 2B-C).

Fig. 1
Water pH in different cities of Rio Grande do Sul in the period of 1996 to 2011 (A) mean, (B) minimum and (C) maximum values (Source CORSAN/RS).

Fig. 2
Water hardness in different cities of Rio Grande do Sul in the period of 1996 to 2011 (A) mean, (B) minimum and (C) maximum values (Source CORSAN/RS).

The mean alkalinity values varied between 24-48 mg CaCO3 L-1, and the highest values were found in the southwest of the state (Fig. 3A). The minimum values for this parameter (around 0-10 mg CaCO3 L-1) were observed in the northeast and north-center of the state (Fig. 3B). The maximum alkalinity values were in the southwest of the state, with the cities of Quaraí and Alegrete having the highest values (Fig. 3C).

Fig. 3
Water alkalinity in different cities of Rio Grande do Sul in the period of 1996 to 2011 (A) mean, (B) minimum and (C) maximum values (Source CORSAN/RS).

The mean water turbidity values were lower than 40 NTU in most regions, except the most waters region, which presented the highest values (Fig. 4A). The minimum values demonstrated that most water from Rio Grande do Sul had very low turbidity (0 - 4 NTU) in some months (Fig. 4B). The maximum turbidity values were much higher, with higher values to the north and the highest in the cities of Santa Rosa and Bento Gonçalves (6000 NTU) (Fig. 4C).

Fig. 4
Water turbidity in different cities of Rio Grande do Sul in the period of 1996 to 2011 (A) mean, (B) minimum and (C) maximum values (Source CORSAN/RS).

The highest mean iron level was 9.8 mg L-1 in the city of Caçapava do Sul (in the center of the state), but for most cities examined values were below 2.0 mg L-1 (Fig. 5A). The mean Mn level within the state was below 0.1 mg L-1 and the highest mean value was found in the city of Alegrete, in the southwest of the state (0.25 mg L-1) (Fig. 5B).

Fig. 5
Mean waterborne (A) iron and (B) manganese in various cities of Rio Grande do Sul in the period of 1996 to 2011 (Source CORSAN/RS).

Discussion

Water quality can be affected by several factors, such as climate, size of the watershed, topography, geology, rain and soil type (Wachholz et al., 2011Wachholz, F., W. Pereira Filho & S. C. B. Sartor. 2011. Influência do uso da terra e precipitação pluviométrica na formação de compartimentos aquáticos no reservatório Rodolfo Costa e Silva - RS, Brasil. Geografia, 36: 551-570.; Gaida et al., 2012Gaida, W., W. Pereira Filho, F. Wachholz & C. G. Konrad. 2012. Dinâmica da vegetação e uso da terra com uso do NDVI na bacia hidrográfica do alto Jacuí. Geo UERJ, 23: 684-698.; Mattos et al., 2014Mattos, T. M., M. R. Costa, B. C. T. Pinto, J. L. C. Borges & F. G. Araújo. 2014. To what extent are the fish compositions of a regulated river related to physico-chemical variables and habitat structure? Environmental Biology of Fishes, 97: 717-730.). Previous analysis of water from ponds and streams from Rio Grande do Sul presented mean pHs similar to those found in the different regions of this study (Rheinheimer & Souza, 2000Rheinheimer, D. & R. O. Souza. 2000. Condutividade elétrica e acidificação de águas usadas na aplicação de herbicidas no Rio Grande do Sul. Ciência Rural, 30: 97-104.; Diel et al., 2007Diel, M., R. M. V. Castilhos, R. O. Sousa, L. C. Valh & J. B. Silva. 2007. Nutrientes na água para irrigação de arroz na região Sul do Rio Grande do Sul, Brasil. Ciência Rural, 37: 102-109.; König et al., 2008König, R., C. R. H. Suzin, R. M. Restello & L. U. Hepp. 2008. Qualidade das águas de riachos da região norte do Rio Grande do Sul (Brasil) através de variáveis físicas, químicas e biológicas. Pan-American Journal of Aquatic Sciences, 3: 84-93.; Pimenta et al., 2012Pimenta A. M., L. M. Furlanetto, E. F. Albertoni & C. Palma-Silva. 2012. Water quality in the lotic area of the Antas river before and after the construction of the Monte Claro hydroelectric plant, south Brazil. Acta Limnologica Brasiliensia, 24: 314-325.; Silva et al., 2012Silva, P. A., D. A. Reynalte-Tataje & E. Zaniboni-Filho. 2012. Identification of fish nursery areas in a free tributary of an impoundment region, upper Uruguay River, Brazil. Neotropical Ichthyology, 10: 425-438.), but in water used for human consumption from artesian wells, from the north central region minimum pH values were down to 4.4 and the maximum up to 10.0 (Rheinheimer & Souza, 2000Rheinheimer, D. & R. O. Souza. 2000. Condutividade elétrica e acidificação de águas usadas na aplicação de herbicidas no Rio Grande do Sul. Ciência Rural, 30: 97-104.).

Mean pH values in the Rio Grande do Sul State are within a safe range for juvenile fish farming. However, minimum values indicated that water from a few cities must be alkalinized before using in aquaculture to avoid mortality (Table 1) and/or reduced growth of the native species silver catfish (Rhamdia quelen ) (Copatti et al., 2005Copatti, C. E., I. J. Coldebella, J. Radünz Neto, L. O. Garcia, M. C. Rocha & B. Baldisserotto. 2005. Effect of dietary calcium on growth and survival of silver catfish juveniles, Rhamdia quelen (Heptapteridae), exposed to different water pH. Aquaculture Nutrition, 11: 345-350.; 2011Copatti, C. E., L. O. Garcia, M. A. Cunha, B. Baldisserotto & D. Kochhann. 2011a. Interaction of water hardness and pH on growth of silver catfish, Rhamdia quelen , juveniles. Journal of the World Aquaculture Society, 42: 580-585.; Baldisserotto, 2011Baldisserotto, B. 2011.Water pH and hardness affect growth of freshwater teleosts. Revista Brasileira de Zootecnia, 40: 138-144.) and Argentinian silverside (Odontesthes bonariensis ) (Gómez et al., 2007Gómez, S. E., R. C. Menni, J. G. Naya & L. Ramirez. 2007. The physical-chemical habitat of the Buenos Aires pejerrey, Odontesthes bonariensis (Teleostei, Atherinopsidae), with a proposal of a water quality index. Environmental Biology of Fishes, 78: 161-171.), or exotic species common carp (Cyprinus carpio ) (Heydarnejad, 2012Heydarnejad, M. S. 2012. Survival and growth of common carp (Cyprinus carpio L.) exposed to different water pH levels. Turkish Journal of Veterinary and Animal Science, 36: 245-249.) and Nile tilapia (Oreochromis niloticus ) (El-Sherif & El-Feky, 2009El-Sherif, M. S. & A. M. I. El-Feky. 2009. Performance of Nile tilapia (Oreochromis niloticus) fingerlings. I. Effect of pH. International Journal of Agriculture & Biology, 11: 297-300.; Cavalcante et al., 2012Cavalcante, D. D., S. R. Silva, P. D. Pinheiro, M. M. F. Akao & M. V. C. Sa. 2012. Single or paired increase of total alkalinity and hardness of water for cultivation of Nile tilapia juveniles, Oreochromis niloticus . Acta Scientiarum, Technology 34: 177-183.). Maximum pH values (9.3) were outside the safe range for aquaculture only in the City of Rio Grande (Table 1), but since these are mean monthly values and not absolute maximum values it is likely that alkaline pH values may eventually occur in some cities from the western and eastern regions of this state. Acidic (pH 5.0) and alkaline water (pH 9.0) altered metabolic parameters and osmoregulation of R. quelen (Bolner & Baldisserotto, 2007Bolner, K. C. S. & B. Baldisserotto. 2007. Water pH and urinary excretion in silver catfish Rhamdia quelen . Journal of Fish Biology, 70: 50-64.; Bolner et al. , 2014Bolner, K. C. S., C. E. Copatti, F. L. Rosso, V. L. Loro & B. Baldisserotto. 2014. Water pH and metabolic parameters in silver catfish (Rhamdia quelen ). Biochemical Systematics and Ecology, 56: 202-208.).

Table 1
Minimum and maximum pH values in which there is 100% survival in the juveniles of certain species of teleost fish raised in southern Brazil. nd: not determined (adapted from Parra & Baldisserotto, 2007Parra, J. E. G. & B. Baldisserotto. 2007. Effect of water pH and hardness on survival and growth of freshwater teleosts. Pp. 135-150. In: Baldisserotto, B., J. M. Mancera & B. G. Kapoor(Eds.). Fish osmoregulation. Enfield, Science Publishers.).

In the Upper Paraná River basin (Southern Brazil), a greater abundance of larval South American silver croaker (Plagioscion squamosissimus ) (Baumgartner et al., 2008Baumgartner, G., K. Nakatani, L. C. Gomes, A. Bialetzki, P. V. Sanches & M. C. Makrakis. 2008. Fish larvae from the upper Parana River: do abiotic factors affect larval density? Neotropical Ichthyology, 6: 551-558.; Reynalte-Tataje et al., 2011Reynalte-Tataje, D. A., K. Nakatani, R. Fernandes, A. A. Agostinho & A. Bialetzki. 2011. Temporal distribution of ichthyoplankton in the Ivinhema River (Mato Grosso do Sul State/Brazil): influence of environmental variables. Neotropical Ichthyology, 9: 427-436.), highwaterman catfish (Hypophthamus edentatus ) and trahira (Hoplias malabaricus ) was positively associated with a higher water pH (7.4-8.5), while the presence of larval piava fish (Leporinus elongatus ) was associated with a pH around 6.8 (Baumgartner et al. , 2008Baumgartner, G., K. Nakatani, L. C. Gomes, A. Bialetzki, P. V. Sanches & M. C. Makrakis. 2008. Fish larvae from the upper Parana River: do abiotic factors affect larval density? Neotropical Ichthyology, 6: 551-558.). The larvae of streaked prochilod (Prochilodus lineatus ) had a better chance of survival at an alkaline pH (8.7-9.2) (Zaniboni Filho et al., 2009Zaniboni-Filho, E., A. P. O. Nuñer, D. A. Reynalte-Tataje & R. L. Serafini. 2009. Water pH and Prochilodus lineatus larvae survival. Fish Physiology and Biochemistry, 35: 151-155.) with the highest rate of survival of post-larval forms when eggs are incubated at a pH of 7.0-8.5 (Reynalte-Tataje et al. , 2015Reynalte-Tataje, D. A., B. Baldisserotto & E. Zaniboni Filho. 2015. The effect of water pH on the incubation and larviculture of curimbatá Prochilodus lineatus (Valenciennes, 1837) (Characiformes: Prochilodontidae). Neotropical Ichthyology, 13: 179-186.). Greater numbers of juvenile P. lineatus and pike cichlid (Crenicichla lacustris ) were also observed in more alkaline water (pH 8.0-8.2), while greater numbers of catfish (Pimelodus maculatus ) were observed in water of a lower pH (6.9-7.2) in Paraíba do Sul River, southeastern Brazil (Araújo et al., 2009Araújo, F. G., B. C. T. Pinto & T. P. Teixeira. 2009. Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology. Hydrobiologia, 618: 89-107.). The larvae of R. quelen also have better growth at a slightly alkaline pH (8.0-8.5) (Lopes et al., 2001Lopes, J. M., L. V. F. Silva & B. Baldisserotto. 2001. Survival and growth of silver catfish larvae exposed to different water pH. Aquaculture International, 9: 73-80.), but incubation can be performed at a pH of 6.0-9.0 (Ferreira et al., 2001Ferreira, A. A., A. P. O. Nuñer & J. R. Esquivel. 2001. Influência do pH sobre ovos e larvas de jundiá, Rhamdia quelen (Osteichthyes, Siluriformes). Acta Scientiarum, Biological Sciences, 23: 477-481.). Juveniles of this species reduced growth when exposed to pH 5.5 or 9.0 (Copatti et al., 2005Copatti, C. E., I. J. Coldebella, J. Radünz Neto, L. O. Garcia, M. C. Rocha & B. Baldisserotto. 2005. Effect of dietary calcium on growth and survival of silver catfish juveniles, Rhamdia quelen (Heptapteridae), exposed to different water pH. Aquaculture Nutrition, 11: 345-350.; 2011aCopatti, C. E., L. O. Garcia, M. A. Cunha, B. Baldisserotto & D. Kochhann. 2011a. Interaction of water hardness and pH on growth of silver catfish, Rhamdia quelen , juveniles. Journal of the World Aquaculture Society, 42: 580-585.,bCopatti, C. E., L. O. Garcia, D. Kochhann, M. A. Cunha, A. G. Becker & B. Baldisserotto. 2011b. Low water hardness and pH affect growth and survival of silver catfish juveniles. Ciência Rural, 41: 1482-1487.). Consequently, considering the pH, the best regions of Rio Grande do Sul to perform incubation and larviculture of most of these species are the west and southeast regions, in which at least the highest values are close to pH 8.0.

The water hardness values in Rio Grande do Sul indicate that the water is usually soft. The city of Caçapava do Sul and the western region of the state contain reserves of calcite and/or dolomite minerals (Brasil, 1973Brasil. 1973. Levantamento de reconhecimento dos solos do estado do Rio Grande do Sul. Boletim Técnico n° 30. Recife, Ministério da Agricultura, 431 p.; Remus et al., 2000Remus, M. V. D., L. A. Hartmann, N. J. McNaughton, D. I. Groves & I. R Fletcher. 2000. The link between hydrothermal epigenetic copper mineralization and the Caçapava granite of the Brasiliano cycle in southern Brazil. Journal of South American Earth Sciences, 13: 191-216.; Oliveira & Kerber, 2009Oliveira, E. V. & L. Kerber. 2009. Paleontologia e aspectos geológicos das sucessões do final do Neógeno no sudoeste do Rio Grande do Sul, Brasil. Gaea - Journal of Geoscience, 5: 21-34.), which can explain the high water hardness values of the water near these cities. Mean values observed in this study were similar to those previously found in the northern region of this state (Silva et al., 2012Silva, P. A., D. A. Reynalte-Tataje & E. Zaniboni-Filho. 2012. Identification of fish nursery areas in a free tributary of an impoundment region, upper Uruguay River, Brazil. Neotropical Ichthyology, 10: 425-438.). Previous studies also detected that the main ions related to water hardness, Ca2+ and Mg2+, presented low levels in Rio Grande do Sul (Diel et al., 2007Diel, M., R. M. V. Castilhos, R. O. Sousa, L. C. Valh & J. B. Silva. 2007. Nutrientes na água para irrigação de arroz na região Sul do Rio Grande do Sul, Brasil. Ciência Rural, 37: 102-109.; Kochhann et al., 2013Kochhann, D., E. R. Behr, A. Chaves, M. F. Mesko, V. L. Dressler, E. M. M. Flores & B. Baldisserotto. 2013. Environmental quality evaluation of the Vacacaí River, Rio Grande do Sul, Brazil. Environmental Earth Sciences, 70: 1727-1733.; Panizzon et al., 2013Panizzon, J. P., V. R. M. Macedo, V. Machado & L. M. Fiuza. 2013. Microbiological and physical-chemical water quality of the rice fields in Sinos River's basin, Southern Brazil. Environmental Monitoring and Assessment, 185: 2767-2775.), in accordance with the mean low water hardness noted in this study.

The response to increasing water hardness varies from species to species. Juveniles of R. quelen maintained at pHs of 4.0, 7.0 and 9.5 survived for at least 96 h with hardness up to 600 mg/L CaCO3 L-1 (higher levels were not tested) even with direct transfer from soft water. Water hardness from 25 to 50 mg CaCO3 L-1 (increased with CaCl2.2H2O) did not affect growth of R. quelen juveniles kept at a pH of 6.0 to 8.0 (Copatti et al ., 2011aCopatti, C. E., L. O. Garcia, M. A. Cunha, B. Baldisserotto & D. Kochhann. 2011a. Interaction of water hardness and pH on growth of silver catfish, Rhamdia quelen , juveniles. Journal of the World Aquaculture Society, 42: 580-585.,bCopatti, C. E., L. O. Garcia, D. Kochhann, M. A. Cunha, A. G. Becker & B. Baldisserotto. 2011b. Low water hardness and pH affect growth and survival of silver catfish juveniles. Ciência Rural, 41: 1482-1487.), neither did the increase of water hardness from 30 to 180 mg CaCO3 L-1 in those kept at a pH of 7.0. However, when kept in very soft water (zero water hardness) R. quelen juveniles must be raised in a pH of 6.0 to avoid mortality and lower growth (Copatti et al ., 2011bCopatti, C. E., L. O. Garcia, D. Kochhann, M. A. Cunha, A. G. Becker & B. Baldisserotto. 2011b. Low water hardness and pH affect growth and survival of silver catfish juveniles. Ciência Rural, 41: 1482-1487.). On the other hand, those maintained at a pH of 7.6 presented lower growth with an increase in water hardness (Ferreira et al., 2013Ferreira, F. W., R. B. Cunha & B. Baldisserotto. 2013. The survival and growth of juvenile silver catfish, Rhamdia quelen , exposed to different NH3 and hardness levels. Journal of the World Aquaculture Society, 44: 293-299.). Therefore, in general, the pH and water hardness of Rio Grande do Sul are appropriate for the aquaculture of R. quelen juveniles, since the regions that have a pH around 6.0 also have very low water hardness, and those with a higher or lower pH usually have higher water hardness.

Water hardness higher than 100 mg CaCO3 L-1 increased the 96 h survival of R. quelen at very acidic (3.75) and alkaline (10.0 and 10.5) pHs (Townsend & Baldisserotto, 2001Townsend, C. R. & B. Baldisserotto. 2001. Survival of silver catfish fingerlings exposed to acute changes of water pH and hardness. Aquaculture International 9: 413-419.). The increase of water hardness from 30 to 60 mg L-1 CaCO3 also improved the growth of R. quelen juveniles exposed to a pH of 5.5, but decreased growth in those kept at a pH of 9.0 (Copatti et al ., 2011aCopatti, C. E., L. O. Garcia, M. A. Cunha, B. Baldisserotto & D. Kochhann. 2011a. Interaction of water hardness and pH on growth of silver catfish, Rhamdia quelen , juveniles. Journal of the World Aquaculture Society, 42: 580-585.). Larvae of this species kept at a pH of 8.0 to 8.5 showed the highest survival and growth at both 30 and 70 mg CaCO3 L-1 (Townsend et al ., 2003Townsend, C. R., L. V. F. Silva & B. Baldisserotto. 2003. Growth and survival of Rhamdia quelen (Siluriformes, Pimelodidae) larvae exposed to different levels of water hardness. Aquaculture, 215: 103-108.), but 70 mg CaCO3 L-1 is the best level for incubation and larviculture irrespective of the proportions of Ca2+ and Mg2+ used to increase water hardness (Silva et al., 2003Silva, L. V. F., J. I. Golombieski & B. Baldisserotto. 2003. Incubation of silver catfish, Rhamdia quelen (Pimelodidae), eggs at different calcium and magnesium concentrations. Aquaculture, 228: 279-287., 2005Silva, L. V. F., J. I. Golombieski & B. Baldisserotto. 2005. Growth and survival of silver catfish larvae, Rhamdia quelen (Heptapteridae), at different calcium and magnesium concentrations. Neotropical Ichthyology, 3: 299-304.). Consequently, considering the water hardness, the southern region of Rio Grande do Sul is the best area for incubation and larviculture of R. quelen because at least the maximum values (except the city of Cidreira) are within the best range for this species.

The recommended water hardness for incubation and larviculture of exotic species raised in Rio Grande do Sul, such as rainbow trout (Oncorhynchus mykiss ) and silver carp (Hypophthalmichthys molitrix ) (Baldisserotto, 2009Baldisserotto, B. 2009. Piscicultura continental no Rio Grande do Sul: situação atual, problemas e perspectivas para o futuro. Ciência Rural, 39: 291-299.), are 139-230 (Ketola et al., 1988Ketola, H. G., D. Longacre, A. Greulich, L. Phetterplace & R. Lashomb. 1988. High calcium concentration in water increases mortality of salmon and trout eggs. The Progressive Fish-Culturist, 50: 129-135.) and 300-500 mg CaCO3 L-1 (Gonzal et al., 1987Gonzal, A. C., E. V. Aralar & J. M. F. Pavico. 1987. The effects of water hardness on the hatching and viability of silver carp (Hypophthalmichthys molitrix ) eggs. Aquaculture, 64: 111-118.), respectively. The maximum levels observed in the state are not enough to support normal aquaculture of those species, water hardness levels are even higher than the maximum levels observed in this state, which would not recommend the hatching of these species. In agreement with these observations, there was low survival of eggs and larvae of O. mykiss (3.5% in the post-hatching phase) in a river in the northeast of Rio Grande do Sul (Winckler-Sosinski et al., 2005Winckler-Sosinski, L., A. Schwarzbold & U. H. Schulz. 2005. Survival of rainbow trout Oncorhynchus mykiss Walbaum 1792 (Salmoniformes - Salmonidae) eggs in an altitude stream in southern Brazil. Acta Limnologica Brasiliensia, 17: 465-472.). However, juveniles and adults of this species can be raised without a problem because those stages can survive in very low water hardness (2.5 mg CaCO3 L-1) (Perry & Wood, 1985Perry, S. F. & C. M. Wood. 1985. Kinetics of branchial calcium uptake in the rainbow trout: effects of acclimation to various external calcium levels. Journal of Experimental Biology, 116: 411-433.). On the other hand, H. molitrix is commonly hatched and raised in southern Brazil (Baldisserotto, 2009Baldisserotto, B. 2009. Piscicultura continental no Rio Grande do Sul: situação atual, problemas e perspectivas para o futuro. Ciência Rural, 39: 291-299.), which agrees with the fact that the Yangtze River, the primary natal habitat of H. molitrix , has low water hardness (28-84 mg CaCO3 L-1). Hatching rate and egg size in this species were not significantly affected by water hardness ranging from 28.5 to 259.0 mg/L CaCO3 (Chapman & Deters, 2009Chapman, D. C. & J. E. Deters. 2009. Effect of water hardness and dissolved-solid concentration on hatching success and egg size in bighead carp. Transactions of the American Fisheries Society, 138: 1226-1231.). The hatching rate and the larval growth of another exotic species raised in Southern Brazil, Mozambique tilapia (Oreochromis mossambicus ), was not affected by exposure to water with 2-3 or 88-96 mg L-1 CaCO3 (using CaCl2 or CaSO4 to increase water hardness) (Hwang et al., 1996Hwang, P.-P., Y.-C. Tung & M.-H. Chang. 1996. Effect of environmental calcium levels on calcium uptake in tilapia larvae (Oreochromis mossambicus ). Fish Physiology and Biochemistry, 15: 363-370.). However, growth of male sex reversed juvenile O. niloticus was higher at 146 mg L-1 CaCO3 (increased with CaCO3) than at 82 mg L-1 CaCO3 (Cavalcante et al., 2009Cavalcante, D. H., A. S. Poliato, D. C. Ribeiro, F. B. Magalhães & M. V. C. Sá. 2009. Effects of CaCO3 liming on water quality and growth performance of fingerlings of Nile tilapia, Oreochromis niloticus . Acta Scientiarum, Animal Sciences, 31: 327-333.), indicating that water hardness must be increased to raise this species in this state. As observed with R. quelen , the increase in water hardness also improved survival and physiologic condition of exotic species, such as O. mykiss (McDonald et al., 1980McDonald, D. G., H. Hobe & C.M. Wood. 1980. The influence of calcium on the physiological responses of the rainbow trout, Salmo gairdneri , to low environmental pH. Journal of Experimental Biology, 88: 109-131.), C. carpio (Chezhian et al., 2011Chezhian, A., N. Kabilan, T. S. Kumar & D. S. Selvan. 2011. Influence of different calcium levels and low pH of water on the plasma electrolyte regulation of a fresh water teleost fish Cyprinus carpio var. communies , (Linnaeus, 1958). Current Research Journal of Biological Sciences, 3: 147-154.) and O. niloticus (Cavalcante et al. , 2012Cavalcante, D. D., S. R. Silva, P. D. Pinheiro, M. M. F. Akao & M. V. C. Sa. 2012. Single or paired increase of total alkalinity and hardness of water for cultivation of Nile tilapia juveniles, Oreochromis niloticus . Acta Scientiarum, Technology 34: 177-183.), exposed to acidic water.

The alkalinity values in Rio Grande do Sul follow water hardness values, i.e ., regions with higher water hardness also have higher alkalinity values, probably due to the presence of calcium-alkaline rocks in the soil (Fernandes et al., 1995Fernandes, L. A. D., R. Menegat, A. F. U. Costa, E. Koester, C. C. Porcher, A. Tommasi, G. Kraemer, G. E. Ramgrab & E. Camozzato. 1995. Evolução tectônica do cinturão Dom Feliciano no escudo sul-rio-grandense: parte II - uma contribuição a partir das assinaturas geofísicas. Revista Brasileira de Geociências, 25: 375-384.). Mean alkalinity values observed in this study were in agreement with the low levels verified in previous studies (Pimenta et al., 2012Pimenta A. M., L. M. Furlanetto, E. F. Albertoni & C. Palma-Silva. 2012. Water quality in the lotic area of the Antas river before and after the construction of the Monte Claro hydroelectric plant, south Brazil. Acta Limnologica Brasiliensia, 24: 314-325.; Silva et al., 2012Silva, P. A., D. A. Reynalte-Tataje & E. Zaniboni-Filho. 2012. Identification of fish nursery areas in a free tributary of an impoundment region, upper Uruguay River, Brazil. Neotropical Ichthyology, 10: 425-438.; Kochhann et al., 2013Kochhann, D., E. R. Behr, A. Chaves, M. F. Mesko, V. L. Dressler, E. M. M. Flores & B. Baldisserotto. 2013. Environmental quality evaluation of the Vacacaí River, Rio Grande do Sul, Brazil. Environmental Earth Sciences, 70: 1727-1733.). Alkalinity levels of 63 and 92 mg CaCO3 L-1 did not affect fertilization and hatching rates, survival or growth of R. quelen larvae (Benaduce et al., 2008Benaduce, A. P. S., D. Kochhann, E. M. M. Flores, V. L. Dressler & B. Baldisserotto. 2008. Toxicity of cadmium for silver catfish Rhamdia quelen (Heptapteridae) embryos and larvae at different alkalinities. Archives of Environmental Contamination and Toxicology, 54: 274-282.). The increase in alkalinity from 30 to 130 mg CaCO3 L-1 without a change in pH or water hardness only decreased growth of R. quelen juveniles maintained at high stocking densities (Andrade et al., 2007Andrade, L. S., R. L. B. Andrade, A. G. Becker, L. V. Rossato, J. F. Rocha & B. Baldisserotto. 2007. Interaction of water alkalinity and stocking density on survival and growth of silver catfish, Rhamdia quelen , juveniles. Journal of the World Aquaculture Society, 38: 454-458.). Larvae of P. lineatus and O. niloticus had better growth at an alkalinity of 30 mg CaCO3 mg L-1 compared to 15-20 and 55-60 mg CaCO3 mg L-1 (Rojas et al., 2001Rojas, N. E. T., O. Rocha & J. A. B. Amaral. 2001. O efeito da alcalinidade da água sobre a sobrevivência e o crescimento das larvas do curimbatá, Prochilodus lineatus (Characiformes, Prochilodontidae), mantidas em laboratório. Boletim do Instituto de Pesca, 27: 155-162.; Rojas & Rocha, 2004Rojas, N. E. T. & O. Rocha. 2004. Influência da alcalinidade da água sobre o crescimento de larvas de tilápia do Nilo (Oreochromis niloticus Linnaeus, 1758 Perciformes, Cichlidae). Acta Scientiarum, Biological Sciences, 26: 163-167.; Paes et al., 2011Paes, T. A. S. V., J. M. V. Paes, N. E. T. Rojas, O. Rocha & M. J. S. Wisniewski. 2011. Effects of liming and development of curimbatá (Prochilodus lineatus ) larvae on the abundance of zooplankton in fish ponds. Acta Limnologica Brasiliensia, 23: 386-393.), but these studies used hydrated lime (CaCO3.2H2O) to increase alkalinity, which also changed water hardness. The increase in alkalinity from 22 to 80 mg CaCO3 mg L-1 with the addition of Na2CO3 (without changing water hardness) did not affect any growth parameter of male sex reversed juveniles of O. niloticus (Cavalcante et al., 2010Cavalcante, D. H., R. L. Barros & M. V. C. Sá. 2010. Growth performance of Nile tilapia, Oreochromis niloticus , fingerlings reared in Na2CO3 limed waters. Acta Scientiarum, Animal Sciences, 32: 331-336.) nor improved growth of those raised in acidic water (Cavalcante et al. , 2012Cavalcante, D. D., S. R. Silva, P. D. Pinheiro, M. M. F. Akao & M. V. C. Sa. 2012. Single or paired increase of total alkalinity and hardness of water for cultivation of Nile tilapia juveniles, Oreochromis niloticus . Acta Scientiarum, Technology 34: 177-183.), demonstrating that for this species water hardness is more important. Therefore, apparently, alkalinity is not a parameter that will affect the aquaculture of native or exotic fishes in Rio Grande do Sul.

The mean turbidity values in Rio Grande do Sul were up to 40 NTU, but in some periods many cities had very high turbidity (up to 6,000 NTU). Low turbidity values (3-97 NTU) were also observed in other studies of rivers in this state (Petry & Schulz, 2006Petry, A. C. & U. H. Schulz. 2006. Longitudinal changes and indicator species of the fish fauna in the subtropical Sinos River, Brazil. Journal of Fish Biology, 69: 272-290.; Salomoni et al., 2006Salomoni, S. E., O. Rocha, V. L. Callegaro & E. A. Lobo. 2006. Epilithic diatoms as indicators of water quality in the Gravatai river, Rio Grande do Sul, Brazil. Hydrobiologia, 559: 233-246.; König et al., 2008König, R., C. R. H. Suzin, R. M. Restello & L. U. Hepp. 2008. Qualidade das águas de riachos da região norte do Rio Grande do Sul (Brasil) através de variáveis físicas, químicas e biológicas. Pan-American Journal of Aquatic Sciences, 3: 84-93.; Blume et al., 2010Blume, K. K., J. C. Macedo, A. Meneguzzi, L. B. Silva, D. M. Quevedo & M. A. S. Rodrigues. 2010. Water quality assessment of the Sinos River, Southern Brazil. Brazilian Journal of Biology, 70: 1185-1193.; Pimenta et al., 2012Pimenta A. M., L. M. Furlanetto, E. F. Albertoni & C. Palma-Silva. 2012. Water quality in the lotic area of the Antas river before and after the construction of the Monte Claro hydroelectric plant, south Brazil. Acta Limnologica Brasiliensia, 24: 314-325.; Panizzon et al., 2013Panizzon, J. P., V. R. M. Macedo, V. Machado & L. M. Fiuza. 2013. Microbiological and physical-chemical water quality of the rice fields in Sinos River's basin, Southern Brazil. Environmental Monitoring and Assessment, 185: 2767-2775.). High turbidity is associated with a lack of marginal vegetation and deforested areas that favor runoff of sediment during rainy periods (Wachholz et al., 2011Wachholz, F., W. Pereira Filho & S. C. B. Sartor. 2011. Influência do uso da terra e precipitação pluviométrica na formação de compartimentos aquáticos no reservatório Rodolfo Costa e Silva - RS, Brasil. Geografia, 36: 551-570.; Mattos et al., 2014Mattos, T. M., M. R. Costa, B. C. T. Pinto, J. L. C. Borges & F. G. Araújo. 2014. To what extent are the fish compositions of a regulated river related to physico-chemical variables and habitat structure? Environmental Biology of Fishes, 97: 717-730.). The turbidity values recommended by Conselho Nacional do Meio Ambiente (CONAMA-2005Conselho Nacional do Meio Ambiente (CONAMA). 2005. Resolução Conama nº 357 Available from: Available from: http://www.mma.conama.gov.br/conama . [01 - August 2013].
http://www.mma.conama.gov.br/conama...
) are up to 100 NTU (around 69-81 mg L-1 depending on the type of sediment). Costa et al. (2014Costa, S. M., E. Appel, C. F. Macedo & V. L. M. Huszar. 2014. Low water quality in tropical fishponds in southeastern Brazil. Anais da Academia Brasileira de Ciências, 86: 1181-1195.) suggested that higher values are inappropriate for fish farming. Therefore, in general, water in Rio Grande do Sul is adequate for aquaculture based on turbidity, but fish farmers must avoid direct collection of water from rivers and lakes during periods of high turbidity, since the maximum values observed were up to 60 times the maximum recommended value. They can also reduce turbidity by adding calcium sulfate in the water (Przepiora et al., 1997Przepiora, A., D. Hesterberg, J. E. Parsons, J. W. Gilliam, D. K. Cassel & W. Faircloth. 1997. Calcium sulfate as a flocculant to reduce sedimentation basin water turbidity. Journal of Environmental Quality, 26: 1605-1611.). Periods of higher turbidity in southern Brazil are usually associated with periods of soil preparation for soy (September-November) and wheat (April-May) cultivation (Wachholz et al. , 2011Wachholz, F., W. Pereira Filho & S. C. B. Sartor. 2011. Influência do uso da terra e precipitação pluviométrica na formação de compartimentos aquáticos no reservatório Rodolfo Costa e Silva - RS, Brasil. Geografia, 36: 551-570.), in which there is no vegetation covering the soil (Gaida et al., 2012Gaida, W., W. Pereira Filho, F. Wachholz & C. G. Konrad. 2012. Dinâmica da vegetação e uso da terra com uso do NDVI na bacia hidrográfica do alto Jacuí. Geo UERJ, 23: 684-698.). There are no studies analyzing the relationship between turbidity and growth in native fish species, but white sea catfish (Genidens barbus ) and piava (Leporinus copelandii ) were associated with turbidity levels of 200-266 NTU, whereas two spot astyanax (Astyanax bimaculatus ) and lambari (Astyanax parahybae ) were found at up to 83 NTU in the Guandu River, in southeast Brazil (Mattos et al. , 2014Mattos, T. M., M. R. Costa, B. C. T. Pinto, J. L. C. Borges & F. G. Araújo. 2014. To what extent are the fish compositions of a regulated river related to physico-chemical variables and habitat structure? Environmental Biology of Fishes, 97: 717-730.). Piscivorous fish adapted to visual hunting, as in Cynodontidae, prefer clear water (Melo et al., 2009Melo, C. E., J. D. Lima & E. F. Silva. 2009. Relationships between water transparency and abundance of Cynodontidae species in the Bananal floodplain, Mato Grosso, Brazil. Neotropical Ichthyology, 7: 251-256.). Water that is turbid (up to 100 NTU) due to clay or silt can also decrease zooplankton consumption and impair growth of some planktivorous fish (Zingel & Paaver, 2009Zingel, P. & T. Paaver. 2010. Effects of turbidity on feeding of the young-of-the-year pikeperch (Sander lucioperca ) in fishponds. Aquaculture Research, 41: 189-197.), while not affecting others (Stuart-Smith et al., 2007Stuart-Smith, R. D., J. F. Stuart-Smith, R. W. G. White & L. A. Barmuta. 2007. The effects of turbidity and complex habitats on the feeding of a galaxiid fish are clear and simple. Marine and Freshwater Research, 58: 429-435.).

The highest Mn and Fe values occurred in the cities of Alegrete and Caçapava do Sul, respectively. The concentration of both metals in the water is related to their concentration in the soil (Minella et al., 2007Minella, J. P. G., G. H. Merten, J. M. Reichert & D. R. Santos. 2007. Identificação e implicações para a conservação do solo das fontes de sedimentos em bacias hidrográficas. Revista Brasileira de Ciências do Solo, 31: 1637-1646.). The highest Fe concentration in the water near the city of Caçapava do Sul is probably due to copper mining, which provokes erosion of hematite (an iron ore) (Remus et al., 2000Remus, M. V. D., L. A. Hartmann, N. J. McNaughton, D. I. Groves & I. R Fletcher. 2000. The link between hydrothermal epigenetic copper mineralization and the Caçapava granite of the Brasiliano cycle in southern Brazil. Journal of South American Earth Sciences, 13: 191-216.). Water Fe (near the City of Caçapava do Sul) and Mn levels are within the range previously observed by other studies (Reginato et al., 2012Reginato, P. A. R., S. Ahlert, K. C. Gilioli & G. Cemin. 2012. Caracterização hidrogeológica e hidroquímica do aquífero livre localizado no manto de alteração da Formação Serra Geral, na bacia hidrográfica Taquari-Antas, região nordeste do estado do Rio Grande do Sul. Revista Ambiente & Água, 7: 143-162.; Kochhann et al., 2013Kochhann, D., E. R. Behr, A. Chaves, M. F. Mesko, V. L. Dressler, E. M. M. Flores & B. Baldisserotto. 2013. Environmental quality evaluation of the Vacacaí River, Rio Grande do Sul, Brazil. Environmental Earth Sciences, 70: 1727-1733.; Weber et al., 2013Weber, P., E. R. Behr, C. D. Knorr, D. S. Vendruscolo, E. M. M. Flores, V. L. Dressler & B. Baldisserotto. 2013. Metals in the water, sediment, and tissues of two fish species from different trophic levels in a subtropical Brazilian river. Microchemical Journal, 106: 61-66.).

The only study that analyzed the effect of Fe on native fish demonstrated that exposure to Fe at 57 mg L-1 for 3 h increased sodium (Na+) loss in tamoatá (Hoplosternum littorale ) in very soft water and that high Ca2+ (866 mg L-1) levels reduced this Na+ loss (Baldisserotto et al., 2012Baldisserotto, B., L. O. Garcia, A. P. Benaduce, R. M. Duarte, T. L. Nascimento, L. C. Gomes, A. R. C. Gomes & A. L. Val. 2012. Sodium fluxes in Tamoatá, Hoplosternum litoralle , exposed to formation water from Urucu Reserve (Amazon, Brazil). Archives of Environmental Contamination and Toxicology, 62: 78-84.). The growth rate of O. mykiss was not affected by 5-10 mg L-1 Fe (at pH 6.7-7.4, water hardness 287 mg CaCO3 mg L-1), but the pH must be neutral or slightly alkaline (Steffens et al., 1993Steffens, W., T. Mattheis & M. Riedel. 1993. Field observations on the production of rainbow trout (Oncorhynchus mykiss ) under high concentrations of water-borne iron. Aquatic Sciences, 55: 173-178.). Exposure to 23-50 mg L-1 Fe reduced growth of catla (Catla catla ), roho labeo (Labeo rohita ) and migral carp (Cirrhina mrigala ) (Hussain et al., 2011Hussain, S. M., M. Javed, A. Javid, T. Javid & N. Hussain. 2011. Growth responses of Catla catla , Labeo rohita and Cirrhina mrigala during chronic exposure of iron. Pakistan Journal of Agricultural Sciences, 48: 225-230.). Therefore, fish growth could be affected only near Caçapava do Sul, but as this region also has one of the highest mean water hardness values, the effect of Fe may be reduced.

Manganese at 4.2 mg L-1 (hardness around 30 mg CaCO3 mg L-1) increased lipoperoxidation in the kidney and reduced mitochondrial activity in the liver of R. quelen . Higher concentrations (8.4 and 16.2 mg L-1) impaired oxidative parameters in this species (Dolci et al., 2013Dolci, G. S., V. T. Dias, K. Roversi, Kr. Roversi, C. S. Pase, H. J. Segat, A. M. Teixeira, D. M. Benvegnú, F. Trevizol, R. C. S. Barcelos, A. P. K. Riffel, M. A. G. Nunes, V. L. Dressler, E. M. M. Flores, B. Baldisserotto & M. E. Bürger. 2013. Moderate hypoxia is able to minimize the manganese-induced toxicity in tissues of silver catfish (Rhamdia quelen ). Ecotoxicology and Environmental Safety, 91: 103-109.). There are no growth studies with native or exotic species raised in Rio Grande do Sul, but up to 3.94 mg L-1 at 30 mg CaCO3 L-1 did not affect mean time to hatch, mortality or weight after 62 days in sea trout (Salmo trutta ). The increase in water hardness decreased Mn toxicity in this species (Stubblefield et al., 1997Stubblefield, W. A., S. E. Brinkman, P. H. Davies T. D. Garrison, J. R. Hockett & M. W. McIntyre. 1997. Effects of water hardness on the toxicity of manganese to developing brown trout (Salmo trutta ). Environmental Toxicology and Chemistry, 16: 2082-2089.). Apparently, mean water Mn levels in this state are not a matter of concern for fish farming, since the highest levels were 12-fold lower than the level that changed growth in S. trutta . Studies regarding the effects of Fe and Mn levels on growth of native fish are still missing and the effect of the interaction between these metals and water hardness or pH on fish growth are still lacking.

Based on the results of this study, water in Southern Brazil presents adequate levels for fish farming in general, but it is necessary to evaluate pH and water hardness before deciding which species to raise. In addition, fish farmers must have some mechanism to reduce water turbidity, since the turbidity can occasionally increase to a dangerous level. The region near Caçapava do Sul, in spite of having comparatively high water hardness, must be avoided for fish farming due to the high Fe levels.

Acknowledgements

Bernardo Baldisserotto, Luciano de O. Garcia and Waterloo Pereira Filho received CNPq research fellowships and Carine de F. Souza and Felipe C. dos Santos CAPES scholarships.

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Publication Dates

  • Publication in this collection
    2016

History

  • Received
    08 Oct 2015
  • Accepted
    02 Aug 2016
Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá., Av. Colombo, 5790, 87020-900, Phone number: +55 44-3011-4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br