Lysine in the diet of Rhamdia voulezi male broodstocks confined in net cages

Abstract

The focus of this study was to evaluate the effect of lysine on the productive (weight and length gain, apparent feed conversion, specific growth rate and condition factor) and reproductive performance of Rhamdia voulezi males confined in net cages during the first reproductive cycle. The following parameters were assessed: seminal parameters (motility rate and duration, survival, sperm concentration, morphology, pH and osmolarity), hormonal parameters (cortisol and testosterone), testicular tissue (histomorphology), organosomatic indices (gonadosomatic, hepatosomatic and viscerosomatic indices) and composition of essential amino acids, crude protein and moisture of whole carcass. Four hundred fish were used, distributed in a random experimental design with four treatments and four replications in 16 net cages with 25 fish each. The treatments consisted of four different diets prepared so as to contain the following levels of lysine: 1.20, 1.40, 1.60 and 1.80%, with 30% crude protein and 3500 kcal kg(-1) digestible energy for 185 days (Jul./12-Jan./13). Eighteen males were selected per treatment, and they all released semen after slight abdominal pressure. The males were weighed, measured, submitted to hypophysation (2.5 mg kg(-1) carp pituitary extract), and then had their semen and blood collected. The fish were sacrificed by cervical dislocation, dissected, and the testes, liver, fat and guts were removed and weighed. The effects (p < 0.05) for the means of final weight, weight gain, apparent feed conversion and condition factor were observed for the analysis of productive performance. With regard to the reproductive parameters, only the seminal volume was affected (p < 0.05). Thus, the levels of testosterone showed quadratic effect (p < 0.05). The anatomy and the histomorphology of the testes were similar between the treatments during the spermiation period. With regard to the organosomatic indices, there was no influence (p > 0.05) between the treatments. The amino acids in the carcass were not affected (p > 0.05). The increment of lysine in the diet provided linear increase for weight gain and seminal volume and linear decrease for feed conversion in R. voulezi broodstocks confined in net cages. (C) 2014 Elsevier B.V. All rights reserved.