Crescimento e mortalidade do camarão branco Litopenaeus schmitti (Burkenroad, 1936) (Crustacea: Decapoda: Penaeidae) em ambiente natural e em confinamento

Abstract

The present study examined growth and mortality rates of the white shrimp Litopenaeus schmitti (Burkenroad, 1936), in Sepetiba Bay RJ, from sep/2011 to ago/2012 and also juveniles in captivity at stocking densities of 8 (treatment A), 16 (treatment B) and 24 (treatment C) shrimps/m2 for 110 days. Growth was based on modal analysis by Solver (Excel) and at ELEFAN (FISAT) routine, according to the von Bertalanffy growth model. Longevity was calculated by its inverse formula. The overall mortality rates were estimated by the converted catch curve and natural mortality rates were estimated from the growth parameters. In the wild it was found a sex ratio of 1:1. Considering total length, growth parameters estimated by tool Solver for males were: Lt∞ = 206,8 mm, k = 1,84 year-1 and longevity of 2,5 years; females: Lt∞ = 231,5 mm, k = 1,99 year-1 and longevity 2,3 years. At ELEFAN, males were: Lt∞ = 206,8 mm, k = 1,6 year-1 and longevity 2,87 years; females: Lt∞ = 235,3 mm, k = 1,65 year-1 and longevity 2,79 years. Growth parameters compared between sexes differed significantly. Total (Z), natural (M), fishing mortality (F) and the exploitation rate (E) were similar for males and females and the mean values between sexes were: 6,00 (Z), 1,92 (M), 4,09 (F) and 0,68 (E). The high rates of exploitation revealed levels above acceptable. In captivity it was considered the carapace length, Lc∞, with fixed values (average of the sum of the largest male and female found in most collections). It was also analyzed the Lc∞ with unfixed values and growth in weight, W∞. The parameter k and the longevity were estimated by Solver using Lc∞ fixed (47,5 mm) and showed no significant differences among treatments. The average values of the parameter k and longevity were 1,63 years-1 and 2,84 years. Also, no differences among treatments were observed in growth parameters, Lc∞, k and longevity, considering unfixed Lc∞ and both methods (Solver and ELEFAN). The mean values of the parameters (Solver) among treatments were: Lc∞ = 16,53 mm, k = 10,34 years-1 and longevity of 0,45 years (163 days). The mean values of the parameters (ELEFAN) among treatments were: Lc∞ = 16,77 mm, k = 9,31 years-1 and longevity of 0,49 years (181 days). For the weight growth the mean parameters among treatments were: W∞ = 4,95 g, k = 10,25 years-1 and longevity of 0,46 years (166 days). These results indicated that such stocking density did not influenced growth parameters and the mortality rates suggesting that higher densities should be further analyzed.