The effect of diets with different levels of protein and energy on the process of final maturation of the gametes of Rhamdia quelen stocked in cages

摘要

The influence of the interaction between the nutrition of tropical freshwater broodfishes when stocked in an intensive system (cages) and their reproductive cycle has received little attention, and the results obtained until now have been very conflicting. One of the main nutritional demands for any species of fish is the source of energy and protein, which is essential for its maintenance, growth and reproduction. This study was conducted with 6300 jundicL, Rhamdia quelen juveniles (47.0pl5.7g and 17.3pl2.1cm), at Itaipu Power Station, in the town of Santa Helena, ParancL, Brazil, in order to assess the different levels of crude protein (CP) and digestible energy (DE) (A: 25% CP; B: 30% CP; C: 35% CP, with 3250kcalgp# and D: 25% CP; E: 30% CP; F: 35% CP, with 3500kcalgp#) during their first reproductive cycle. Six treatments and three replicates were applied to a total of 18 cages (5.0mpd) with 70fishesmpd each, from January to December/2006. Fishes from each cage were randomly captured, measured (Lt, cm), weighed (Wt, g), and had their gonads (Wg, g) weighed to determine the condition factor (K) and gonado-somatic (GSI) indices. The histomorphological appearance (light microscopy) of the gonads was not affected by the diets of treatments A, B, D, E, or F. However, the highest mean value of GSI was 15% in treatment C (35% CP and 3250kcalgp#), differently from the other treatments (p <0.05). Nevertheless, it could be noticed that in treatment C the mean values of K were very similar for both sexes and had significant differences during the experiment (p <0.05). The asynchronous ovary contained oocytes at all stages of development and had potential to perform fractional spawning up to four times a year (treatment C), with the first maturation beginning in July/06 (28.6pl1.4cm), and then in September (33.2pl0.5cm), October (32.5pl2.7cm) and December (34.4pl3.4cm). The fishes that had received the other diets exhibited only three spawning peaks/year, in September (28.0pl4.8cm), October (28.4pl7.6cm) and December (32.9pl2.0cm). Nevertheless, the males started their maturation process when they were two months old (17.6pl1.9cm), and continued progressively during spermatogenesis, reaching the peak of maturation at the beginning of spermiation. During the regression phase, residual spermatozoa could be observed together with the decrease of the mean values of GSI.