Reproductive intensity of fish assemblages from streams of the Contas river basin, State of Bahia, Northeastern Brazil

Intensidade reprodutiva das assembleias de peixes de riachos da bacia do rio de Contas, Estado da Bahia, Nordeste do Brasil

Abstract

Information about the reproductive biology of fish assemblages is limited, particularly for coastal basins in Northeast Brazil. However, this information is crucial for understanding species' life histories and informing conservation strategies and management actions. The scarcity of studies on the reproductive patterns of stream fish highlights a significant research gap, as this knowledge is essential for the effective conservation of these ecosystems. This study aimed to assess the reproductive intensity of fish assemblages from streams that are part of two drainages of the Contas River basin (Upper Contas and Gongogi River drainages), which are located in two distinct biomes (Caatinga and Atlantic Forest, respectively) in the Northeast Brazil. The fish were collected between November 2012 and November 2013 in four quarterly expeditions that encompassed one seasonal cycle. The captures were conducted by electric fishing in 18 sampling sites, nine in the Upper Contas River drainage and nine in the Gongogi River drainage. We obtained the reproductive intensity index (RII) of the studied assemblage, being the values compared between expeditions, drainages, and sampling sites. The highest values of RII were observed between November/December and February/March in both drainages, which demonstrated that the highest reproductive intensity was associated to the rainy season. In the Upper Contas River streams, the reproductive peak intensity seems to be synchronized to the beginning of the rainy season, while in the Gongogi River drainage streams, the reproductive intensity remains high throughout the entire rainy season. Regarding spatial variation, the highest RII values were observed in smaller streams, probably associated with a more restricted species distribution in these locations. Our results indicate that the assessed streams play a crucial role in the reproduction of many fish species, as evidenced by the high reproductive intensity observed, particularly within the fish assemblage of the Upper Contas River.

Keywords:
ichthyofauna; life history; seasonality; Northeastern Mata Atlântica Freshwater Ecoregion (NMAF); reproduction

Resumo

As informações sobre a biologia reprodutiva das assembleias de peixes são limitadas, particularmente para as bacias costeiras do Nordeste do Brasil. No entanto, essas informações são cruciais para entender o ciclo de vida das espécies e orientar estratégias de conservação e ações de manejo. A escassez de estudos sobre os padrões reprodutivos de peixes de riachos destaca uma lacuna importante na pesquisa, já que esse conhecimento é fundamental para a conservação eficaz desses ecossistemas. Este estudo objetivou avaliar a intensidade reprodutiva das assembleias de peixes de riacho pertencentes a duas drenagens da bacia do rio de Contas (drenagem do Alto rio de Contas e drenagem do rio Gongogi), localizadas em dois distintos biomas (Caatinga e Mata Atlântica, respectivamente) no nordeste do Brasil. Os peixes foram coletados entre novembro de 2012 e novembro de 2013 em quatro expedições de coletas trimestrais, contemplando um ciclo sazonal. As capturas foram conduzidas utilizando pesca elétrica em 18 sítios de amostragem, sendo nove da drenagem do Alto Contas e nove da drenagem do rio Gongogi. Nós calculamos o índice de intensidade reprodutiva (IIR) para as assembleias estudadas e os valores foram comparados entre as estações, drenagens e sítios de amostragem. Os maiores valores de IIR foram observados entre as amostragens de Novembro/Dezembro e Fevereiro/Março em ambas as drenagens, indicando que a elevada intensidade reprodutiva está associada à estação chuvosa. Nos riachos do Alto rio de Contas, o ápice da intensidade reprodutiva aparentemente está sincronizado com o início da estação chuvosa, ao passo que nos riachos da drenagem do rio Gongogi, a intensidade reprodutiva permanece alta em toda a estação chuvosa. Em relação à variação espacial, os maiores valores de IIR foram observados nos riachos de menor porte, o que está provavelmente associado às espécies com distribuição mais restrita que são observados nesses locais. Nossos resultados indicam que os riachos avaliados desempenham um papel crucial na reprodução de muitas espécies de peixes, como evidenciado pela alta intensidade reprodutiva observada, particularmente dentro da assembleia de peixes do Alto Rio de Contas.

Palavras-chave:
ictiofauna; história de vida; sazonalidade; Ecorregião Aquática da Mata Atlântica Nordeste; reprodução

1. Introduction

The current and historical association of human societies with aquatic environments has resulted in significant alterations to these ecosystems, leading to what is known as the ‘freshwater biodiversity crisis’ (Albert et al., 2020; Ottoni et al., 2023). This scenario is alarming since the extinction rates of freshwater organisms are reported to be twice as high as those observed in other environments (Albert et al., 2020; Reid et al., 2019). This situation has raised awareness within the global scientific community, which has made substantial efforts in recent years to propose conservation actions as to reduce the rate loss of freshwater species (Albert et al., 2020; Ottoni et al., 2023; Tickner et al., 2020). Nonetheless, one of the major challenges in developing effective conservation strategies is the lack of a reliable database (Hortal et al., 2015; Reid et al., 2019). This deficiency can lead to inaccurate or biased conceptions of the species’ basic ecology and fundamental niche space (Britnell et al., 2021). Consequently, this incomplete and skewed data may create a “species stereotype”, underestimating intra- or inter-population variation and response curves (Britnell et al., 2021). This, in turn, can lead to erroneous, limited, or incomplete characterization of the species’ biology, ultimately hindering the development of effective conservation strategies (Britnell et al., 2021; Christie et al., 2020; Hortal et al., 2015). In this context, Hortal et al. (2015) identified seven categories of knowledge gaps concerning global biological diversity, among of which the lack of information on species’ life history, functional roles, and responses to habitat changes is associated to Hutchinsonian and Raunkiaeran shortfalls.

Reproduction is a fundamental process in the life history of organisms, serving as the mechanism through which genetic material is passed from one generation to the next (Wootton and Smith, 2014). Factors such as timing, spatial distribution, and resource availability are crucial for reproductive success (Wootton, 1984). In this context, most Neotropical fish species exhibit a cyclical reproductive pattern, alternating between periods of low or no reproductive activity and phases of heightened reproductive intensity, during which higher survival rates are observed for individuals in the early stages of life (Wootton and Smith, 2014). Photoperiod and temperature are related to those cyclical patterns acting as environmental triggers that modulate gonadal development stages (Wootton and Smith, 2014). In addition to these extrinsic factors, other environmental characteristics are important indicators of favorable conditions for spawning, such as water level variation throughout the year (Caramaschi and Brito, 2021). Many Neotropical fish species have their reproductive period concentrated in the most intense part of the rainfall season (Caramaschi and Brito, 2021; Lowe-McConnell, 1999; Wootton and Smith, 2014). Under these conditions, the expansion of water bodies is generally observed, leading to the establishment of new habitats, which provide shelter and protection for younglings (Agostinho et al., 2004; Andrade and Braga, 2005; Vazzoler, 1996; Winemiller et al., 2008).

Assessing the reproductive dynamics of fish communities requires detailed and precise measurements of species physiology, anatomy, and behavior. However, this dataset may not guarantee the desired information, as some species are sampled from constantly shifting population strata (Vazzoler, 1996). The presence of individuals with mature gonads in a particular area is not a definitive indicator of spawning, since these individuals may remain there to feed and complete gonadal development before migrating to established spawning grounds (Vazzoler, 1996). To address these limitations, the Reproductive Intensity Index (RII) was developed as a tool for analyzing assemblage-level dynamics, focusing on determining whether spawning occurs and at what intensity within the system (Vazzoler, 1996). This is achieved through the identification of females ready to reproduce and their representation in the area (Vazzoler, 1996). A study conducted on the fish community of the Passa Cinco stream (state of São Paulo, Brazil) used the RII to assess the reproductive activity of species across different seasons and locations within the stream, which contributed to a better understanding of how environmental factors, such as rainfall patterns, influences fish reproductive process (Rondineli and Braga, 2010).

When we consider that the reproductive strategies and tactics of freshwater fish are closely linked to climatic factors such as temperature, photoperiod, and rainfall, as well as the structural characteristics of aquatic environments (Caramaschi and Brito, 2021; Vazzoler, 1996; Wootton and Smith, 2014), it is expected that fish fauna will respond differently when comparing communities immersed in distinct physiographic regions. In this context, this research was conducted in the Contas River basin, a river system located in the Northeast region of Brazil, influenced by two biomes: Caatinga (upper and middle stretches) and Atlantic Forest (lower stretch) (INEMA, 2024), resulting in a high physiographic and climatic variability. This river basin harbors streams that support a rich ichthyofauna, accompanied by a high degree of endemism (Barreto et al., 2018; Silva et al., 2020; Zanata and Serra, 2010; Zanata et al., 2019), nonetheless it remains relatively unexplored. Previous studies conducted in the Contas River basin (e.g., Silva, 2015; Souza et al., 2020) have shed light on the fish composition, taxonomy, functionality, and trophic structure. However, there are no studies specifically focused on the reproduction of fish species in this basin. In fact, there are some studies on the reproduction of freshwater fish species in the northeastern coastal basins, but they are mainly concentrated on main drainage channels or artificial reservoirs (e.g., Barros et al., 2016; Chellappa et al., 2003, 2009; Gurgel et al., 2011; Gurgel et al., 2012). Additionally, it is important to note that the reproductive information currently used for populations and communities in this region is largely based on data from studies conducted on the ichthyofauna either from the southeastern river basins or the São Francisco River basin. This underscores the importance of the present study, which starts to fill the significant knowledge gap in regarding the reproductive biology of stream fish in the northeastern coastal river basins.

In this study, we assessed the variation of the seasonal reproductive intensity of fish assemblages from the Upper Contas River drainage, in Chapada Diamantina region (Caatinga biome), and in the Gongogi River drainage streams (Atlantic Forest biome). Our predictions are: i) The RII of fish assemblages in both the Upper Contas River and Gongogi River drainages will be significantly higher during the rainy season when compared to the dry season. This increase is expected due to the higher availability of resources and optimal spawning conditions, which are typically associated with the rainy periods in Neotropical environments; ii) The variation in RII will be more pronounced in the Upper Contas River drainage streams than in the Gongogi River streams. This is based on the greater seasonality observed in the Upper Contas River region, where environmental conditions such as water flow and temperature fluctuate more dramatically throughout the year, thus influencing reproductive behaviors in fish; and iii) The RII is expected to vary according on the abiotic and structural variables of streams, as these factors directly and indirectly influence fish biology, leading to various adaptations that allow fish to occupy and reproduce in these habitats (Caramaschi and Brito, 2021; Lowe-McConnell, 1999).

2. Material and Methods

2.1. Study area

The Contas River watershed presents 55,483 km² in area, encompassing around 76 municipalities (INEMA, 2024). The river source is in the municipality of Piatã, State of Bahia, Northeastern Brazil, at 1,600 m of altitude, between the municipalities Serras do Atalho and Serra da Tromba. Its mouth is in the Atlantic Ocean, in the municipality of Itacaré, State of Bahia. This river basin is in the Northeast Atlantic Forest aquatic ecoregion (Abell et al., 2008), and its main rivers are the Upper Contas, Brumado, Gavião, Antônio, Sincorá, Gentio, Lower Contas, Gongogi, Coastal and Transitional. The Contas River basin presents humid, sub-humid, and semi-arid climates, with the latter encompassing an area of 51% of the basin (INEMA, 2024; Figure 1).

Figure 1
Historical total monthly rainfall (the average of the last 30 years) for the Upper Contas drainage region (average values for Contas River and Piatã) and the drainage region of the Gongogi River (average values for the municipalities of Gongogi, Dário Meira, Coaraci and Ibicuí). Grey columns represent the months in which the expeditions were conducted. Source: Climatempo (2015).

This study was performed in two drainages from the Contas River, which include two biomes: Caatinga and Atlantic Forest (Figure 2). The Upper Contas River drainage is mainly composed by perennial streams (Bahia, 1993). Despite its location in the Caatinga biome and presenting remnants of typical Caatinga arboreal/shrubby vegetation, it is also influenced by the Cerrado biome vegetation, which includes Rocky Outcrops (Campo Rupestre), Open Grassland (Campo Limpo), and Wooded Savanna (Cerrado Stricto Sensu) physiognomies (Brasil, 2024). The Gongogi River drainage is located in an Atlantic Forest region, where remnants of the Inland Seasonal Atlantic Forest and Coastal Seasonal Atlantic Forest are found. In addition to the Atlantic Forest, pasture and “cabruca” (cocoa forest) areas are also present in the landscape (Brasil, 2024).

Figure 2
Contas River hydrographic basin (Bahia State, Brazil) with the sampling points in the two evaluated drainages (circles - sampled sites belonging to the Gongogi River drainage, diamond - sampling sites belonging to the Upper Contas River drainage). Light grey: Caatinga Biome, Dark grey: Atlantic Forest Biome.

2.2. Sampling of biological material

The fishes were collected during the study developed by Silva (2015). In this sense, four quarterly expeditions were performed between November 2012 and November 2013, thus encompassing one seasonal cycle. Eighteen stretches of wadable streams from first to third order (Strahler), were sampled based on a 1:10,000 scale map: nine located in the Upper Contas River drainage and nine in the Gongogi River drainage (Figure 2). The fish capture was conducted by electric fishing (Smith-Root backpack electrofisher apparatus; model LR-24; 800V DC). In each stream, a stretch of 50 meters without block nets was covered from downstream to upstream. Fishes subjected to the electric field were immediately collected with hand nets. The collected individuals were anesthetized (1 g/L benzocaine solution) (Brasil, 2013), fixed at 10% formaldehyde, for seven days, and were kept in identified plastic bags with alcohol 70%.

2.3. Specimens’ identification and classification

The specimens’ identification was based on specialized literature for each fish group and was performed with the assistance of experts. The taxonomic classification followed Fricke et al. (2024a). All taxon names, as well as their respective authors, year of publication and the validity status were checked in Fricke et al. (2024b). The assessed specimens are maintained in the Zoology Collection of the Universidade Estadual do Sudoeste da Bahia. The vouchers specimens were deposited in the Zoology Museum of the Universidade Federal da Bahia (MZUFBA).

2.4. Specimens analysis

The following biometric data of each specimen were measured in the laboratory: total weight, total length and standard length. After abdominal incision, the sex, gonadal maturation stage and gonad weight were determined (Braga, 1990; Caramaschi and Brito, 2021; Vazzoler, 1996).

The gonadal maturation stage of each female specimen was determined macroscopically by assessing several ovarian characteristics, including color, transparency, superficial vascularization, and the appearance of oocytes (Vazzoler, 1996). The categories assigned to the gonadal maturation stages were: A) immature gonads; B) maturing or resting; C) mature gonads; and D) spent. Although Vazzoler (1996) distinguishes between the maturing (B) and resting (E) stages, we combined them into a single category, as we were unable to macroscopically differentiate between these stages based on oocyte diameter or the thickness of the ovuligerous lamellae. Nonetheless, since only females with mature ovaries (C) were considered for the RII calculation, this adjustment did not affect our results.

2.5. Data analysis

The reproductive intensity of fish assemblages in different expeditions, sampling sites, and drainages was assessed using the Reproductive Intensity Index (RII) (Vazzoler, 1996). This method is based on the relationship between the frequency of females with mature gonads (maturation stage = C) and the gonadosomatic relationship (GSR) of females. The GSR indicates the percentage of an individual's total weight represented by the gonads and is calculated using the formula: GSR = (GW / BW) × 100, where GW is the gonad weight and BW is the body weight. The species’ reproductive categories were defined according to the following reference attributes: %C and %GSRmax. %C represents the reproductive activity and is expressed as the frequency of females with mature gonads (mature stage = C) in all sampled unit, being considered high when equal to or greater than 15% (see Vazzoler, 1996). %GSRmax represents the functional status of the ovaries and serve as evidence of spawning in the system when population mean GSR values are equal to or greater than 30% of observed maximum GSR for entire sampled population (see Vazzoler, 1996). Based on these criteria, the species were classified into the following categories: 1) Massive Spawning – MS (%C ≥ 15% and %GSRmax ≥ 30%); 2) Occasional Spawning – OS (%C < 15% and %GSRmax ≥ 30%); 3) Incipient Maturation – IM (%C ≥ 15 and %GSRmax < 30%); and 4) No Reproductive Activity – NRA (%C < 15% and %GSRmax <30%). A weight (W) was assigned to each category as follows: MS: W = 4; OS: W = 2; IM: W = 1; NRA: W = 0 (Vazzoler, 1996). Afterwards, the RII was obtained for each sample by calculating the weighted average, taking into account the weight corresponding to the categories assigned to each assessed species (Equation 1).

$RII=\frac{\sum P*Nsp}{\sum Nsp}$ (1)

where: P = each category score; Nsp = number of species per category.

Some criteria were established to include species in the RII calculation, as to prevent low-abundant species from interfering in the analysis (see Vazzoler 1996). 1) only species with at least 10% of reproductive females (maturation state = C or D), relative to the total number of sampled individuals, were selected for the RII calculation. 2a) For each expedition, the RII was calculated using species with at least ten female individuals in each drainage; 2b) for site-specific RII calculations, only species that represented at least 50% of the total local abundance and had at least six female individuals at each sampling site were considered.

The drainages were compared by analyzing the pattern of RII variation between expeditions using a paired t-test. Mean RII values were compared between the drainages using a t-test, treating each sampling site as replicate. The relationship between the RII values obtained for each sampling site and their abiotic characteristics were assessed by using multiple linear regression. Therefore, the average values of the abiotic variables used in Silva (2015) between expeditions were considered (Table 1). Subsequently, it was compared to each other through a correlation analysis, as to identify the collinear variables. Variations were considered autocorrelated when the r value was equal to or greater than 0.60. After this first screening, a stepwise forward selection procedure was implemented to identify the best variables set for the linear regression model. The following variables were selected: width, depth, catchment area, and pH.

Table 1
Median, minimum (Min.), and maximum (Max.) abiotic variables values that were evaluated in the Contas River basin ichthyofauna sampling sites (Silva, 2015). The autocorrelated variables excluded from the other analyses are indicated by X.

VARIABLES	Median	Min.	Max.	Autocorrelated variables
Altitude (m)	531	160	1330	X
Substrate composition (%)				X
Sand	16.7	0.9	88.7
Gravel/Pebble	7.6	0.0	86.7	X
Boulder/ Stone bed	51.0	0.0	99.1	X
Accumulated plant material	6.45	0.0	88.9	X
Canopy cover (%)	40.0	0.0	83.1	X
Average current speed (m/s)	1.5	0.0	6.9	X
Average depth (cm)	23.8	9.7	59.1
Average width (m)	4.5	1.5	15.0
Water temperature (°C)	23.7	17.0	30.4
Conductivity (μS/cm)	0.01	0.00	0.28	X
pH	6.7	3.6	8.2
Dissolved oxygen in water	7.7	1.0	9.4	X
Catchment area (km2)	71.44	13.89	1060.91
Annual precipitation (mm)	942	691	1249
Seasonality (Monthly variation coefficient)	50.69	22.02	75.73

3. Results

A total of 6,243 fish specimens, belonging to 40 species, 16 families and five orders, were analyzed (Table 2). From these, sixteen species met the selection criteria for calculating the RII between expeditions (Table 2). For the Upper Contas River drainage, the species considered were Astyanax aff. lacustris (Lütken 1875), Characidium sp. 4 (sensuOliveira-Silva et al., 2024), Hyphessobrycon brumado Zanata and Camelier, 2010, Parotocinclus jimi Garavelo 1977, Poecilia reticulata Peters 1859, Psalidodon aff. fasciatus, Serrapinnus heterodon (Eigenmann 1915), and Rhamdia aff. quelen. For the Gongogi River drainage, the species were A. lacustris, Apareiodon itapicuruensis Eigenmann and Hen 1916, Cetopsorhamdia sp., Characidium sp.1 (sensuOliveira-Silva et al., 2024), Characidium sp.4 (sensuOliveira-Silva et al., 2024), Deuterodon burgerai (Zanata and Camelier 2009), Hemigrammus aff. marginatus, Pareiorhaphis sp.2, Phenacorhamdia tenebrosa (Schubart 1964), Parotocinclus cristatus Garavello 1977, P. reticulata and P. aff. fasciatus. Two of these species are endemic to the Contas River basin, the H. brumado and P. jimi, as for the P. reticulata, it was the only invasive species recorded here.

Table 2
Individuals of the fish species evaluated in the drainages of Upper Contas River and Gongogi rivers, belonging to the Contas River basin (BA), classified according to their respective orders and families. The data correspond to expeditions 1 (Nov-Dec/2012), 2 (Feb-Mar/2013), 3 (Jun/2013), and 4 (Aug-Sep/2013).

Order, Family, Species	Code	Drainage		Total number of individuals
		Upper Contas River	Gongogi River
Characiformes		1435	2104	3539
Acestrorhynchidae
Acestrorhynchus falcatus (Bloch 1794)	Ac_fal		1	1
Anostomidae
Leporinus bahiensis Steindachner 1875	Le_bah		7	7
Megaleporinus brinco (Birindelli, Menezes and Britski 2013) @	Le_bri	2	1	3
Acestrorhamphidae
Astyanax aff. lacustris	As_lac	75	48	123
Deuterodon burgerai (Zanata and Camelier 2009)	Dt_burg		212	212
Hasemania piatan Zanata and Serra 2010@	Ha_pia	3		3
Hemigrammus aff. marginatus	He_mar	11	424	435
Hyphessobrycon brumado Zanata and Camelier 2010 @	Hy_bru	369		369
Nematocharax venustus Weitzman, Menezes and Britski 1986	Ne_ven		31	31
Oligosarcus macrolepis (Steindachner 1877)	Ol_mac		6	6
Psalidodon aff. fasciatus	Ps_fas	321	712	1033
Characidae
Serrapinnus heterodon (Eigemann 1915)	Se_bra	559		559
Serrapinnus piaba (Lütken 1875)	Se_het		164	164
Crenuchidae
Characidium sp.1 (sensuOliveira-Silva et al. 2024)	Ch_sp1		267	267
Characidium sp.4 (sensuOliveira-Silva et al. 2024)	Ch_sp4	68	92	160
Curimatidae
Cyphocharax pinnilepis Vari, Zanata and Camelier 2010 @	Cy_pin		48	48
Erythrinidae
Hoplias aff. malabaricus	Ho_bra	24	24	48
Hoplias brasiliensis (Spix and Agassiz 1829)	Ho_mal	1	11	12
Parodontidae
Apareiodon itapicuruensis Eigenmann and Henn1916	Ap_ita		22	22
Serrasalmidae
Serrasalmus brandtii Lütken 1875	Se_pia	2	34	36
Cichliformes		18	208	226
Cichlidae
Cichlasoma sanctifranciscense Kulander 1983	Ci_san	1		1
Geophagus multiocellus Mattos and Costa 2018	Ge_mul		208	208
Geophagus sp.1 (sensu Argolo et al. 2020)	Ge_sp1	17		17
Cyprinodontiformes		128	60	188
Poeciliidae
Poecilia reticulata Peters 1859*	Po_ret	128	60	188
Gymnotiformes		9	7	16
Gymnotidae
Gymnotus bahianus Campos-da-Paz and Costa 1996	Gy_ba	9	4	13
Gymnotus aff. carapo	Gy_car		3	3

Siluriformes		952	1322	2274
Callichthyidae
Hoplosternum littorale (Hancock, 1828)	Ho_lit	2		2
Heptapteridae
Cetopsorhamdia sp.	Ce_sp	4	153	157
Phenacorhamdia tenebrosa (Schubart 1964)	Pt_cri	9	61	70
Pimelodella itapicuruensis Eigenmann 1917	Pi_ita	1	7	8
Rhamdia aff. quelen	Rh_que	51	11	62
Loricariidae
Hypostomus sp.1	Hy_sp1		466	466
Hypostomus sp.2	Hy_sp2		114	114
Hypostomus sp.3	Hy_sp3	199		199
Pareiorhaphis sp.1	Pa_sp1	85		85
Pareiorhaphis sp.2	Pa_sp2	1	285	286
Parotocinclus cristatus Garavello 1977	Ph_ten		93	93
Parotocinclus jimi Garavello 1977@	Pt_jim	307	2	309
Trichomycteridae
Ituglanis agreste Lima, Neves and Campos-Paiva 2013@	It_agr	9	11	20
Trichomycterus cf. tete	Tr_tet	284	119	403
Total		2542	3701	6243

• ^*
  Invasive species;
• ^@endemic to the Contas River basin. Adapted from Silva (2015).

Species were allocated into reproductive categories by expedition, drainage and the values from each category (Table 3). For both drainages, the number of species classified as massive spawning (MS) was proportionally higher in expedition 1 and 2. In contrast, species without reproductive activity (NRA) were more frequent in expedition 3, and secondarily, in expedition 4. In this sense, the highest RII values were observed in expeditions 1 and 2 for both drainages (t = 0.3464; p = 0.752) (Table 3, Figure 3). The RII values per sampling site ranged between 2.0 and 4.0 (Tables 4 and 5, Figure 4), with the highest values obtained for Upper Contas River sites (t = 2.7042; p = 0.021).

Table 3
Reproductive categories (MS: Massive spawning, OS: Occasional spawning, IM: Incipient maturation, and NRA: No reproductive activity) and Reproductive Intensity Index (RII) values by drainage for the species codes (Table 2) in the four collection periods corresponding to expeditions 1, 2 3, and 4 (1 – nov./dec.; 2 – feb./mar.; 3 – jun.; 4 – aug./sep.). [The Supplementary Data 1 summarizes the proportion of mature females (maturation stage = C) and the GSRc average value related to the GSRmax for each considered species for the expeditions and drainages].

	Expeditions
Species – Code	1	2	3	4
Upper Contas drainage
As_lac	MS	MS	NRA	-
Ch_sp4	MS	MS	OS	-
Hy_bru	MS	MS	OS	MS
Po_ret	MS	IM	MS	MS
Ps_fas	MS	MS	NRA	IM
Pt_jim	IM	MS	NRA	NRA
Rh_qual	-	NRA	-	-
Se_het	MS	OS	NRA	NRA
RII	3.4	2.9	1.1	1.8
Gongogi River drainage
Ap_ita	-	MS	-	-
As_lac	-	OS	-	-
Ce_sp	MS	MS	NRA	OS
Ch_sp4	-	MS	NRA	NRA
Ch_sp1	MS	MS	NRA	IM
Dt_burg	MS	MS	MS	OS
He_mar	OS	OS	OS	OS
Pa_sp.2	MS	OS	NRA	OS
Ph_ten	IM	MS	NRA	NRA
Po_ret	-	-	MS	MS
Ps_fas	MS	IM	NRA	NRA
Pt_cri	IM	MS	IM	MS
RII	3	3.2	1.1	1.7

• - Data absence.

Figure 3
Fish assemblages' Reproductive Intensity Index (RII) from the expeditions (1 – nov./dec.; 2 – feb./mar.; 3 – jun.; 4 – aug./sep.) in the Upper Contas River and Gongogi river drainages of the Contas River basin (BA).

Table 4
Reproductive categories (MS: Massive spawning, OS: Occasional spawning, IM: Incipient maturation, and NRA: No reproductive activity) and values of the species' Reproductive Intensity Index (RII), by sampling site of the Upper Contas River drainage (UC). The corresponding code to the species is shown in Table 2. [The Supplementary Data 2 summarizes the proportion of mature females (maturation stage = C) and the GSRc average value related to the GSRmax for each considered species for the Upper Contas River drainage sampling sites].

Species (RGSmax)	UC1	UC2	UC3	UC5	UC6	UC9
As_lac	MS	-	MS	MS	MS	-
Ch_sp4	MS	MS	-	-	-	MS
Gy_ba	MS	-	-	-	-	-
He_mar	NRA	-	-	-	-	-
Hy_bru		-	-	MS	OS	-
It_agr	OS	-	-	-	-	-
Ph_ten		MS	-	-	-	-
Po_ret	MS	MS	MS	-	MS	-
Ps_fas	MS	MS	-	-	-	MS
Pt_jim	MS	-	MS	IM	NRA	MS
Rh_que		-	MS	-	-	-
Tr_tet		-	OS	MS	OS	OS
RII	3.30	4.00	3.50	3.25	2.40	3.50

• - Data absence.

Table 5
Reproductive categories (MS: Massive spawning, OS: Occasional spawning, IM: Incipient maturation, and NRA: No reproductive activity) and values of the species’ Reproductive Intensity Index (RII), by sampling site of the Gongogi River drainage (GG). The corresponding code to the species is shown in Table 2. [The Supplementary Data 3 summarizes the proportion of mature females (maturation stage = C) and the GSRc average value related to the GSRmax for each considered species for the Gongogi River drainage sampling sites].

Species (RGSmax)	GG2	GG3	GG5	GG6	GG7	GG8	GG9
Ap_it	-	-	NRA	-	-	MS	-
As_lac	-	OS	-	OS	-	-	-
Ce_sp	MS	-	-	OS	MS	-	-
Ch_sp4	OS	-	-	-	-	-	OS
Ch_sp1	-	-	-	OS	MS	MS	MS
Dt_burg	-	-	-	MS	-	MS	-
He_mar	OS	OS	-	-	-	-	MS
It_agr	-	-	-	OS	-	-	-
Pa_sp2	-	-	OS	OS	OS	OS	-
Ph_ten	-	-	-	MS	IM	-	-
Po_ret	-	-	MS	-	-	MS	-
Ps_fas	OS	OS	-	IM	NRA	NRA	MS
Pt_cri	-	-	-	-	-	-	MS
Tr_tet	-	-	OS	-	-	-	-
RII	2.50	2.00	2.00	2.43	2.20	2.80	3.60

• - Data absence.

Figure 4
Fish assemblages' Reproductive Intensity Index (RII) from the sampling sites in the Upper Contas River (UC) and Gongogi River (GG) drainages of the Contas River basin (BA). The dashed line represents the average RII obtained for each drainage from the RII values of the respective sampling sites.

The multiple linear regression indicated a significant relation between the RII values and the considered abiotic variables (p = 0.0116), with a high model determination coefficient (r² = 0.77). It is important to highlight that the pH had not presented a significantly slope different from 0 (t = -1.6577; p = 0.136; r² = 0.177). Catchment area, depth and width were significantly related to RII (Catchment area: t = 2.486; p = 0,038; r² = 0.015. Depth: t = -2.7498; p = 0.025; r² = 0.343. Width: t= -3.0024; p = 0,017; r² = 0.264). It is noteworthy that only the latter two variables had higher r² values, both of which were negatively correlated with the RII values.

4. Discussion

The highest reproductive intensities were obtained between the months of November/December and February/March (Expeditions 1 and 2), corresponding to the historically wettest period in the region. This supports our first hypothesis, which predicted that the reproductive intensity would be higher in the periods of increased rainfall. These findings are consistent with studies on the reproductive intensity of Neotropical fish communities (Gomiero and Braga, 2007; Rondineli and Braga, 2010; Vazzoler, 1996). In the tropics, rainfall and rising water levels are primary triggers for teleost reproduction (Lowe-McConnell, 1999; Rizzo et al., 1996; Winemiller et al., 2008), as they increase the availability of reproductive substrates through the expansion of water surface area (Wootton and Smith, 2014), and enhance food and shelter availability for offspring (Caramaschi and Brito, 2021; Vazzoler, 1996). Most species with higher proportions of female with mature gonads and elevated mean GSR values were observed during expeditions 1 (November-December) and 2 (February-March), indicating their reproductive periods. However, it is important to note that some species, such as P. reticulata, D. burgerai, H. brumado, and P. cristatus, likely reproduce over an extended period, as mature females were found in all expeditions. This is not uncommon in stream-dwelling fish species, which often reproduce throughout the year (Alkins-Koo, 2000; Casatti, 2003; Garutti, 1989; Gomiero et al., 2008; Mazzoni and Petito, 1999; Mazzoni et al., 2002; Santos et al., 1995; Vicentin et al., 2012), particularly those with low fecundity and parental care (Mazzoni and Caramaschi, 1995). The prolonged reproductive period observed in some species may also be associated with multiple spawning, a strategy that reduces competition among juveniles and optimizes resource use (Nikolski, 1963). This strategy is particularly advantageous in unstable environments, such as streams, where reproduction is not limited to a single period, thus mitigating the risks posed by stochastic factors (Caramaschi and Brito, 2021). The “piabas” A. lacustris, D. burgerai, H. brumado, S. heterodon, and P. fasciatus also presented mature gonads throughout the year, but with higher relative values of mature females and GSR in expeditions 1 and 2, during the rainy period. Similar results were obtained for other “piabas” (families Acestrorhamphidae and Characidae), typical of streams (Alkins-Koo, 2000; Mazzoni and Petito, 1999; Oliveira et al., 2023; Santos et al., 1995; Souza et al., 2015a; Vicentin et al., 2012). These small “characids” have a life history strategy that would be classified as opportunistic (sensuWinemiller 1989; Winemiller and Rose 1992), represented by small-bodied species with early maturation, continuous reproduction, low fecundity but high reproductive effort, rapid population turnover and capacity for rapid colonization (Blanck et al., 2007; Lamouroux et al., 2002; Winemiller 1989).

The reproductive intensity (RII) varied similarly between expeditions in both drainages, which conflicted with our hypothesis stating that the variation in reproductive intensity throughout the year would be higher in the Upper Contas River drainage streams when compared to the Gongogi River. Considering that, historically, rainfall in the Gongogi River region is better distributed throughout the year, it was expected that the reproductive intensity values would not differ much between expeditions in this drainage. Yet, the unexpectedly low variation in RII between expeditions in highly seasonal environments must be highlighted. The use of historical data through interpolation methods provided by INMET probably limited the assessment of the real effect of rainfall on the reproductive intensity of the assessed fish communities. In this regard, it is important to note that the sampling expeditions coincided with the greatest water scarcity period to affect the Gongogi River drainage region (G1 BA, 2013). This situation has little impact on the historical average, but it could be responsible for the low RII values observed for this drainage in expedition 3. It is essential to emphasize that historical data was needed since the studied region lacks climatological stations, which made it impossible to collect data on the rainfall of specific locations during the period in which the samplings occurred. In addition to rainfall, other environmental factors may be associated with the beginning of the reproductive period. The photoperiod and temperature, for instance, are also associated with the final gonads’ maturation, at least for the ichthyofauna of streams at higher latitudes (Portella et al., 2021; Souza et al., 2015b; Suzuki et al., 2004). Souza et al. (2015b) when investigated the environment-life history associations for Deuterodon intermedius (Eigenmann 1908) (=Astyanax intermedius) (Acestrorhamphidae), did not find a positive relation between rainfall and the reproductive effort of the species, which were in a headwater stream in the Atlantic Forest. On the other hand, the authors found that the reproductive effort of males is relatively constant throughout the year, while for females it increases with higher water temperature, relating to a possible trade-off with the somatic growth and survival of this small stream fish. Considering that the photoperiod is associated with latitude and that both drainages are situated at similar latitudes, we understand that it was not a predominant factor in our study. Silva (pers. observation.) assessed the water temperature at each sampling site in every expedition and found a higher average temperature in the Gongogi River drainage streams than that observed in the Upper Contas River drainage streams. The greatest difference was found between August/September (Expedition 4) and November/December (Expedition 1). Thus, even being a superficial assessment, temperature is not strongly related to reproductive intensity in this region.

The multiple regression indicated that the reproductive intensity is more pronounced in smaller streams, as evidenced by the values obtained for each sampling site. In larger streams, there is a grouping of species typical of these environments and more common to river species (e.g. A. lacustris, Geophagus spp., Hoplias spp., Hypostomus spp., P. fasciatus, and R. quelen) that use the streams to fulfill some stages of the life cycle (food, growth, or reproduction). Therefore, this transient fauna does not necessarily reproduce in the stream, which negatively interferes with the RII values. On the other hand, species with more restricted distribution to these environments (e.g., Characidium sp.1, D. burgerai, H. brumado, I. agreste, Parotocinclus spp., and Trichomycterus cf. tete) are observed completing their life cycle in these smaller locations.

Processes related to the distribution and dispersal of fish species, associated with the climatic and hydrological characteristics of the studied regions, may explain the differences observed between the drainages. The streams of the Gongogi River drainage exhibited lower RII values compared to those of the Upper Contas River. In the latter, the higher-order portions are represented by long stretches of a temporary nature, making the dispersion process difficult. Thus, even common river species are more restricted to the upper perennial stretches of the drainage and probably reproduce locally. As for the Gongogi River drainage, the water availability (resulting from high rainfall levels) allows a greater connection between rivers and streams, favoring the species dispersal. With a more significant dispersion, fluxes allow species registration in different reproductive categories at the same sampling site, which influences the RII value.

It is important to note that the presence of P. reticulata, a widely introduced species in Neotropical basins (Fricke et al.,2024b), directly influenced the results obtained, as its reproductive data were included in the RII calculations. This species was classified as having a massive spawning during the two expeditions conducted in the dry season, which contributed positively to the RII values for this period in both evaluated drainages. In this context, without the interference of this artificial component, it is plausible to assume that the difference in RII values between the two basins would have been even greater.

Compared with studies that evaluated reproductive intensity using the same methodology for other Neotropical fish assemblages, our results can be considered higher. The RII values obtained for the expeditions 1 and 2 (with a maximum of 3.4 and 2.8 for the Upper Contas River, and 3 and 3.2 for the Gongogi River, respectively) surpass those found by Rondineli and Braga (2010) in the rainy period in the Passa Cinco River (3.17) and by Gomiero and Braga (2007) in the Corumbataí basin (2.62 and 2.25) and Jacaré-Pepira basin (2.25), in the southeastern region. Both studies focused on larger watercourses where species in rivers and streams were observed with different sizes. In addition, possibly a significant part of their representatives does not reproduce in the sampled locations. Therefore, the highest values observed in the present study may be related to the fact that the ichthyofauna considered in the RII analyzes are typical of streams. This perception is based on the high number of species included in the massive and occasional spawning categories.

This study provides valuable insights into the spatial and temporal variation in the reproductive intensity of Neotropical fish. The use of the Reproductive Intensity Index (RII) is particularly noteworthy as it offers critical information on the reproductive ecology of fish communities. However, the application of RII remains limited in the scientific literature, likely due to the significant effort required for both data collection and methodology implementation. It is important to acknowledge that, despite our efforts, several species could not be included in the RII analysis due to the low number of specimens collected. Therefore, any extrapolation of our findings should be made with caution. While this limitation prevents the comprehensive assessment of all species within the community, it does not undermine the relevance of this approach. On the contrary, it underscores the necessity for further investment in more extensive studies and collaborative research initiatives to maximize the potential use of the RII in advancing our understanding of fish reproductive ecology.

Streams, along with all other freshwater ecosystems, are the most threatened environments in the world (MEA, 2005). These environments present several communities, supporting a high proportion of biodiversity (Dudgeon, 2020). The Contas River basin and the other basins of the Northeast Atlantic Forest aquatic ecoregion exhibit high species richness accompanied by a high degree of endemism (Silva et al., 2020). The composition of its ichthyofauna involves species occurring partially or entirely in streams, what indicates a potential risk for these populations, since the impacts of anthropic activities in such environments are alarming, mainly considering deforestation, damming of watercourses for the formation of reservoirs, and the waste disposal (Silva, 2015). The assessed streams are fundamental for many species, as they are associated with high reproductive intensity, especially in the Upper Contas River region. Information about the reproduction of fish species can aid in assessing environmental quality, as well as supporting the management and conservation of both species and streams (Caramaschi and Brito, 2021). The reproductive aspects presented here, along with the works of Silva (2015) on the composition and structure of stream fish assemblages, and Souza et al. (2020) on the trophic ecology of stream fishes, provided a more robust picture of the Contas River basin ichthyofauna. These results are important since it comprises about 31% of all species in the northeastern Atlantic Forest Aquatic Ecoregion (Silva, 2015). Finally, our study demonstrated that the RII effectively captured detailed information in reproductive intensity in relation to seasonality, with a higher concentration of reproductive individuals observed during the rainier months. Given the scarcity of reproductive studies in these environments, our results are crucial for advancing the understanding of fish assemblage life histories in streams, which are highly dynamic and unpredictable systems across different biomes.

Supplementary Material

Supplementary material accompanies this paper.

Supplementary Data 1:

Individuals' frequency with mature ovaries (%C), mean GSRc (gonadosomatic ratio of mature females), and % GSRmax (GSRc percentage concerning the highest GSR value recorded for the respective species) values for the most representative species in expeditions 1 (Nov-Dec/2012), 2 (Feb-Mar/2013), 3 (Jun/ 2013), and 4 (Aug-Sep/2013). The %C and %GRSmax values considered high are highlighted in bold. The species code is in Table 2.

Supplementary Data 2.

Individuals' frequency with mature ovaries (%C), GSRc means values (gonadosomatic ratio of mature females), and %GSRmax (GSRc percentage concerning the highest GSR value recorded for the respective species) for fish species evaluated at each sampling site of the Upper Contas River drainage (UC). The %C and %GRSmax values considered high are highlighted in bold. The code corresponding to the species is shown in Table 2.

Supplementary Data 3.

Individuals' frequency with mature ovaries (%C), GSRc mean values (gonadosomatic ratio of mature females), and %GSRmax (GSRc percentage concerning the highest GSR value recorded for the respective species) for fish species evaluated at each sampling site of the Gongogi River drainage (GG). The %C and %GRSmax values considered high are highlighted in bold. The corresponding code to the species is shown in Table 2.

This material is available as part of the online article from https://doi.org/10.1590/1519-6984.287407

Acknowledgements

The authors thank the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) for the financial support (process number 2012/58050-8320), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) for the partial financial support (Finance Code 001), Instituto Chico Mendes de Conservação da Biodiversidade (ICMBIO-SISBIO) for the collection license granted (number 33398-1), Fundação de Amparo à Pesquisa do Estado de Bahia (FAPESB) for the scholarship granted to Martins, M. S., and all those who assisted in the fieldwork. We also thank the anonymous referees for their comments and suggestions.

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Publication Dates

• Publication in this collection
  31 Jan 2025
• Date of issue
  2024

History

• Received
  08 June 2024
• Accepted
  20 Nov 2024