Relação peso-comprimento da ictiofauna do rio Jaguaribe, Ceará, Brasil

Abstract

Mathematical models, such as the weight-length relationship, allow comparisons between different fish populations, providing major information that supports a better comprehension of the populational dynamics of the ichthyofauna in different systems. The objective of this study was to assess the weight-length relationship in 19 species of fishes of the Jaguaribe river basin (Ceará, Brazil), located in the semiarid region of Brazil. Fish gathering were made in 16 points, affluent streams and in the main channel of the upper, middle and lower parts of Jaguaribe river, during the rainy season in March and April of 2014 and in April and May of 2015. At each sampling point, a stretch of 50 meters was delimited by using networks that prevented the escape of the ichthyofauna. Posteriorly in this stretch, fish gathering were made with trawl net, sieve net and a seine net and separated by sample habitats (aquatic macrophytes, ponds e pools). Collected individuals were cryoanesthetized by emerging in eugenol solutions, subsequently fixed in formalin 10% and conservated in alcohol 70%. In the Water Ecology laboratory at the Federal University of Ceará, the weight (in grams) and the length (in millimeters) were measured using precision analytical balance and digital caliper. To determine the weight-length relationship, using the statistical software R an analysis of the linear regression was made from the model generated by the log-transformed equation: logW = loga + b x logSL, where W is the weight and SL the standard length. A total of 4742 individuals were evaluated, presenting a coefficient of determination (r²) between 0,950 and 0,999; standard length varying between 0,807 and 17,00 cm; the coefficient a between 0,0059 and 0,0340; and the values of b varying between 2,610 and 3,711. Among the species of fish evaluated, five (Characidium bimaculatum, Ctenobrycon spillurus, Serrasalmus rhombeus, Steindachnerina notonota e Triportheus signatus) presented isometric growth, one (Serrasalmus heterodon) negative isometric growth and the others (13) positive isometric growth. The weight-length relationship was also used to evaluate the effects of habitats (aquatic macrophytes, ponds e pools) in the distribution of species, as well as the population segregation patterns obtained through comparisons between confidence intervals, observing the non-overlapping of the evaluated parameters resulting from the effects of bus in the upper, middle and lower compartments of the Jaguaribe sub-basin and the temporal variation of the population. The results of the weight-length relationship provide a better understanding of the population dynamics of Brazilian semiarid fish species and of processes currently investigated (such as growth patterns in the ichthyofauna) in intermittent ecosystems.