Parasites in Leporinus macrocephalus ( Anostomidae ) of four fi sh farms from the western Amazon ( Brazil )

This study evaluated the presence of metazoan parasites in Leporinus macrocephalus from four fi sh farms from the western Amazon (Brazil). In 160 fi sh examined, prevalence was 61.9%, and parasites found were: Urocleidoides paradoxus, Urocleidoides eremitus, Tereancistrum parvus, Jainus leporini, Procamallanus (Spirocamallanus) inopinatus, Rhabdochona (Rhabdochona) acuminata, Dolops discoidalis and Ergasilus sp., but U. paradoxus was the dominant parasite. Jainus leporini and Ergasilus sp. occurred only in L. macrocephalus from one fi sh farm, while U. paradoxus, U. eremitus and T. parvus were found in fi sh from three fi sh farms. Dolops discoidalis, P. (S.) inopinatus and R. (R.) acuminata occurred only in L. macrocephalus from two fi sh farms. Higher infection levels were caused by U. paradoxus, U. eremitus and P. (S.) inopinatus, which had an aggregated dispersion. There was positive correlation between abundance of parasites and the length of hosts. No difference in the condition factor of parasitized and non-parasitized fi sh were found. Such differences between fi sh farms were attributed to differences in management and quality of cultivation environments, and data indicate the need to adopt prophylactic measures in the fi sh farms to prevent diseases in the future. This was the fi rst report of D. discoidalis and Ergasilus sp. for L. macrocephalus.


INTRODUCTION
Leporinus macrocephalus Garavello & Britski, 1988; popularly known as piauçu or piavussu, is an endemic Anostomidae fi sh to the Paraguay River basin and can reach up to 60 cm in length; hence it is an important fi shery resource and also valuable for aquaculture of some Brazilian regions. Among the species of the genus Leporinus, L. macrocephalus is the largest species. Thus, it had been cultivated mainly in the Southeast Brazilian region, once it presents high weight gain, high feed conversion, fast growth, tasty meat and rusticity to cultivation (Andrade et al. 2006, Capodifoglio et al. 2015. However, recently, L. macrocephalus has also been reared in the State of Acre, in northern Brazil (Martins et al. 2017a, b).
As the State of Acre has great potential for fi sh farming, in 2015 there was the creation of a state industrial complex to produce fi sh native to Amazon, to intending boost the activity to around 2,162 fi sh farmers. Thus, in 2017, the State of Acre produced 8,000 tons of farmed fi sh, mainly native species, including L. macrocephalus. In 2018, this production had an increase of 6.3% and reached 8,500 tons (PeixeBR 2019). Despite the economic importance of L. macrocephalus for the fi sh farming in the State of Acre, little is known about its parasite fauna and epidemiological indices.
For L. macrocephalus farmed in the northeastern region of the State of São Paulo, the following parasites have been reported: Henneguya leporinicola Martins, Souza, Moraes & Moraes, 1998(Martins et al. 1999 (Martins et al. 2017a, b). Therefore, as there is no study on the parasite fauna of L. macrocephalus in the municipality of Rio Branco, the aim of this study was to investigate the metazoan parasites for this fish reared in four fish farms from this municipality.

Ethical disclosures
This study was developed in accordance with the principles adopted by the Brazilian College of Animal Experimentation (COBEA), and authorization from Ethics Committee in the Use of Animal of the Embrapa Amapá (#013/2018) was carried out.
From June 2015 to May 2017, 160 L. macrocephalus were collected in four fish farms (i.e., 40 specimens in each fish farm) in the municipality of Rio Branco, State of Acre (Brazil), for analysis of metazoan parasites. Each fish farm had different characteristics of management and structure (i.e., fish size, stocking density, sanitary quality, quality and source of water supply, etc.) ( Table I). Fish from fish farm 1 were produced by the property, and the water supply of the tanks originates from the property. Fish from fish farms 2 and 3 were acquired from different suppliers of fingerlings, and the source of water supply for tanks in fish farm 2 is a river, but in fish farm 3 the source of water supply for tanks originates from the property. Fish from fish farm 4 were acquired from a supplier of fingerlings that made antiparasitic treatments using sodium chloride. The source of supply of the tanks of this fish farm originates from the property.
During fish collection, the pH was determined using a digital pH meter in each fish farm, as well as temperature (CDS107) and dissolved oxygen concentration, using a digital oximeter (HQ40D).
For each necropsied fish, we examined the mouth, opercula, gills, gastrointestinal tract and viscera. Gills were removed, fixed in 5% formalin and analyzed using a stereomicroscope (SMZ 800N, Nikon, Tokyo, Japan) and microscope (Eclipse E100, Nikon, Tokyo, Japan). The gastrointestinal tract and viscera were removed and examined under a stereomicroscope for collection of endoparasites. The methodology used for collecting, fixing, counting and preparing the parasites for identification followed previous recommendations (Eiras et al. 2006).
The ecological terms used followed previous recommendations of Bush et al. (1997). The frequency of dominance (percentage of infracommunities in which a parasite species is numerically dominant) was determined (Rohde et al. 1995). The dispersion index (DI) and discrepancy index (D) were calculated using the Quantitative Parasitology 3.0 software, to detect the distribution pattern of parasite infracommunities (Rózsa et al. 2000), for species with prevalence >10%. The significance of DI, for each intracommunity, was tested using the d-statistics (Ludwig & Reynolds 1988).
Weight and total length of fish were used to calculate the relative condition factor (Kn) of parasitized and non-parasitized fish (Le Cren 1951), which were compared using the Mann-Whitney (U) test. The Spearman correlation coefficient (rs) was estimated to determine possible correlations between length and weight of host fish and the abundance of parasites (Zar 2010).

RESULTS
The specimens of L. macrocephalus examined had different body size due to the different stages of cultivation (fingerlings and fattening). Total parasite prevalence was high in fish farms 1-3 (Table I). In general, these fish farms had different management strategies and stocking density of L. macrocephalus and the size of this host.
In the four fish farms, pH and temperature were similar, but the levels of dissolved oxygen in water were low in fish farms 2-4 (Table II), which also had inadequate sanity conditions.
Monogeneans J. leporini occurred only in L. macrocephalus from fish farm 3, while U. paradoxus, U. eremitus only do not occurred in fish farm 4. However, T. parvus and R. (R.) acuminata occurred in fish from fish farms 1-3. Procamallanus (S.) inopinatus occurred in fish from fish farms 1 and 2, while Dolops discoidalis Bouvier, 1399 and Ergasilus sp. were found only in fish from fish farm 2 (Table III). In L. macrocephalus, the high infection levels were caused by U. paradoxus, U. eremitus and P. (S.) inopinatus, but the dominance was of U. paradoxus. The parasites presented an aggregated dispersion (Table IV).

DISCUSSION
In L. macrocephalus of four fish farms from Rio Branco, State of Acre, the parasitic prevalence was 61.9%. Similar prevalence was reported by Martins et al. (2017a) for this same fish cultured in thanks and dam in Cruzeiro do Sul, State of Acre. However, this was higher than the prevalence (21.3%) reported by Martins et al. (2002) for L. macrocephalus from fish farms in the State of São Paulo. Half of the fish farms investigated here presented low levels of dissolved oxygen in water and the majority had inadequate sanity conditions, which favored the prevalence of parasites found. However, in the four fish farms studied, fish did not present macroscopic signals of diseases, due to low to moderate levels of parasitism. In general, the parasitism rate in L. macrocephalus has been attributed to stocking density and poor water quality, which favors the dissemination of infectious stages of parasites (Tavares-Dias et al. 2001a, b, Martins et al. 2002, 2017a. Also, U. paradoxus, U. eremitus and P. (S.) inopinatus were the parasites with higher prevalence in L. macrocephalus, and they showed a high aggregated dispersion, a pattern also found by Martins et al. The condition factor is a quantitative indicator of fish welfare that can be used as a tool for studying the relationship between host health status and parasitism (Le Cren 1951, Santos et al. 2013, Morey & Arellano 2019. Thus, relative condition factor was used to evaluate the body condition in L. macrocephalus of the present study, and this was similar between parasitized and non-parasitized fish and no correlation between the parasitic load and relative condition factor was found, due to the moderate infection levels that not caused damages to the hosts. Similar results were reported for L. macrocephalus also infected by metazoan parasites found in the current study. Determining the factors that affect the presence of parasites is important to parasitology study. In fish populations, body size can influence parasite load (Santos et al. 2013, Martins et al. 2017a, Morey & Arellano 2019; however, it    were reported (Martins et al. 2017a) and five of these parasite species were also found in the present study. Also, L. macrocephalus from fish farm 4 was represented by fingerlings recently purchased for fattening. Therefore, these fish did not have time to re-infect themselves in the fish farm and also acquired other parasite species. Larvae of P. (S.) inopinatus have copepods as intermediate hosts and are ingested by fish, which are the definitive hosts of this nematode, an endoparasite frequent in wild fish that can also infect farmed fish (Hamann 1999, Martins et al. 2017a, Neves et al. 2020

CONCLUSIONS
For L. macrocephalus, the parasite community was composed of species of monogeneans, nematodes and crustaceans, parasites with low to moderate infection levels and aggregated dispersion. The parasitism was influenced by the different management strategies of fish farms, mainly to the stocking density of L. macrocephalus and the size of this host, as well as by the oxygen levels in water, which varied among the fish farms. As expected, there was a low diversity of endoparasites, which depend on the presence of intermediate hosts with infective stages to maintain their complex life cycle. This was the first report of D. discoidalis and Ergasilus sp. for L. macrocephalus. Lastly, it was the second report of P. (S.) inopinatus and R. (R.) acuminata for L. macrocephalus.