Ecologia trófica e reprodutiva de Leporinus piau (Fowler, 1941) (Characiformes) sob influência de áreas florestadas em um rio neotropical

Abstract

The Capibaribe river, totally inserted in the state of Pernambuco, has suffered several impacts that endanger its environmental integrity and aquatic communities, such as fish. Among the impacts, monoculture of sugar cane and urban pollution have caused eutrophication of rivers, and may interfere with the food and reproductive success of the ichthyofauna. Knowledge of the food and reproductive biology of fish is essential to protect natural stocks and can ensure the preservation and abundance of the species. The objective of this study was to evaluate the dietary and reproductive strategies of the Leporinus piau species in a landscape with a predominance of sugarcane, a non-forested area, and a forested area in the low section of the Capibaribe River, Northeast Brazil. The fish samples were collected monthly between September / 2013 and August / 2014 in the cities of São Lourenço da Mata, Paudalho and Recife. Abiotic parameters were measured and water samples were collected for nutrient measurement. The fish were captured through waiting nets with meshes of 12 to 50 mm between adjacent nodes, exposed for 12 hours at night, and then packed and fixed in 10% formalin and preserved in 70% alcohol. The individuals of L. piau were eviscerated for the removal and weighing of the digestive tract and gonads. Food items were identified to the lowest taxonomic level. For feeding, the frequency of occurrence of the items (FO) was applied and the relative weight of the items, calculated the IAi, and the trophic niche amplitude were calculated. For each stomach, the number of different food items present was calculated using analysis of variance (ANOVA). Similarly, the diet was compared using the permutation analysis of variance (PERMANOVA). To represent the samples multivariate, we used Canonical Correlation Analysis (CCA), considering combinations of variables, such as climatic period, land cover and sex. In the reproduction study, the stages of gonadal development were evaluated through macroscopic analysis. The sex ratio was calculated using the chi-square test (X2), calculated the Gonadossomatic Index (IGS), allometric condition factor (K), fecundity, and the reproductive activity index (IAR). The Spearman relation was calculated to evaluate the relationship between the abiotic and reproductive parameters, and the Non-metric Multidimensional Dimension Analysis (NMS) was used to plot the distribution of the species by length class related to the collection sites. Significant differences were found in the proportion between the sexes in the sites, and between the IGS and the collection sites and the quarters of the year. The presence of mature stage, higher number of oocytes in the fecundity and higher value of IAR were found in forested areas and in the third quarter, showing the period of greatest reproduction in the rainy season. The abiotic and reproductive parameters showed a relationship between IGS, maturational stages, inorganic phosphate and total phosphorus. In the NMS analysis, L. piau had preference for forested areas, high reproduction sites. For the study of the feeding, 111 specimens were collected, being the herbivorous and malacófaga species with tendency to occur among the sampled areas. In forested areas, the species presented greater food diversity and wider niches. It was observed that L. piau alters the food preference according to the season showing opportunistic behavior. For the reproduction study, 97 individuals were captured, being 54 males and 43 females. The L. piau species shows a positive allometric growth. The species L. piau is considered seasonal strategist, since its reproductive process is related to the seasonal changes occurred in the aquatic environment.