Fauna de helmintos de juvenis de pirarucu, Arapaima gigas (Schinz, 1822) e aspectos de sua produção no município de Manacapuru-AM

Abstract

In South America, Brazil stands out as the largest producer of freshwater fish and gathers favorable conditions to become one of the largest fish producers in the world. One of the native fish with potential for fish farming is the pirarucu (Arapaima gigas), as long as the problems in its production chain, in the areas of reproduction, nutrition and health, are solved. The lack of a technological package in the production of the species has contributed to a low supply of larvae and fingerlings, in addition to the high mortality rate caused mainly by parasitic and bacterial diseases. With that, the objective of the study was to characterize the A. gigas creations, register the occurrences, identify the species and determine the infestation/parasitic infection rates (Chapter I). This study was carried out in seven fish farms in the municipality of Manacapuru – Amazonas, and recorded information on the structure of rearing, flooded area, water supply source, management and feeding of breeders, larvae and juveniles. Samples of 10 fish were obtained from each fish farm, totaling 70 fish. Each sample corresponded to one spawn of A. gigas in captivity. During these collections, the water quality parameters were recorded. Fish were measured and weighed to calculate the weight-length equation and condition factor. After this step, the fish were analyzed for the presence of parasites, and the specimens found were fixed in 70% ethanol and identified a posteriori. After quantification of the parasites, the parasite indices were calculated. In fish farms, the reproduction, hatchery and rearing of A. gigas were carried out in dams and earthen ponds, supplied with dammed water, an artesian well or a river. Most of the fish farms are dedicated to reproduction and re-creation, the broodstocks were fed live forage fish and the juveniles initially with natural zooplankton, then brine shrimp nauplii until total replacement by powdered commercial feed. The water quality parameters were within the standards for the cultivation of tropical fish species. Fish weight and length were different between fish farms (p<0.05) and the condition factor (Kn=1.2) indicated good body condition of fish. A. gigas showed negative allometric growth (b<3), indicating greater growth in length than in weight. Of the 70 fish examined, 43 were parasitized. A total of 133 parasites were collected and monogenea and digenea were identified and the genera Hysterothylacium sp., Procamallanus (Spirocamallanus) sp. (Nematoda), Neoechinorhynchus sp. and Polyacanthorhynchus sp. (Acanthocephala). The prevalence varied from 30 to 100% (mean 61.4%), the mean intensity from 1.0 to 8.1 (mean 3.1 ± 4.4) and the mean abundance from 0.3 to 5. 7 (mean 1.9 ± 3.8). Monogenea parasites were collected in the gills, digenea encysted in the swim bladder and the larvae of Procamallanus (Spirocamallanus) sp. in the intestine, all with low parasitic indices. The larvae of Hysterothylacium sp. were collected from the entire gastrointestinal tract of A. gigas, mainly the mesentery. Specimens of Neoechinorhynchus sp. were collected from the mesentery, while Polyacanthorhynchus sp. in the intestine. Hysterothylacium sp. presented the highest parasitic indices, followed by Neoechinorhynchus sp. The correlation between parasite abundance and fish relative consition factor was not significant (p > 0.05), but correlations between weight and length and parasite abundance were significant (p < 0.05). It is noteworthy that the parasitic fauna of juveniles of A. gigas is mainly composed of species of endohelminths, the pathogenic nematode Hysterothylacium sp., with zoonotic potential, and the acanthocephalon Neoechinorhynchus sp. In addition, this study described a new species of the phylum Acanthocephala, parasitizing juveniles of A. gigas cultivated in the state of Amazonas (Chapter II). The description of the new species was only possible because all specimens of Neoechinorhynchus sp. were found in adulthood. The new species is distinguished from all others in the genus by a combination of characters including smaller trunk, smaller anterior spines in males, medial and posterior spines of the same size in both sexes, two seminal vesicles below the cement reservoir and in a ventral position. The attachment site of this species differs from all other acanthocephalic species in the mesentery. This is the first species of Neoechinorhynchus described for a fish species of the Arapaimidae family and the tenth species of the genus recorded in Brazil, and the name Neoechinorhynchus arapaimensis is proposed. As measures to prevent and control parasites, it is recommended to: disinfect production structures at the end of the production cycle, eliminate aquatic microphytes, individualize the supply, install a filter or screen at the water collection site, carry out a strict sanitary control in the reuse of water , monitor water quality, carry out fish health assessment, adopt quarantine for fish acquired in other fish farms, offer a mixed diet with fish, feed and vitamin and mineral supplement, feed fish with frozen zooplankton, include immunostimulant additives in the diet, contact specialized technician for disease diagnosis and control measures, disinfecting utensils and keeping employees clean.