Redução no uso de farinha de peixe em dietas suplementadas com atratores alimentares para cultivo do camarão branco, Litopenaeus vannamei

Abstract

Replacement of fishmeal and fish oil in aquaculture diets for more abundant and less expensive protein sources, such as soybean meal and land animal by-products, lead to a reduced feed intake. As shrimp detect and find the food source through chemical stimuli dissolved in water, feed attractiveness becomes an important parameter in low fishmeal diets. The present study aimed at evaluating if the inclusion of feeding effectors in experimental diets with a progressive reduction of Anchovy fishmeal (FPA) and (or) formulated levels of methionine could balance and enhance the growth and feeding responses of the white shrimp, Litopenaeus vannamei. Juvenile shrimp of 3.14 ± 0.60 g body weight were simultaneously stocked in 30 indoor (500-l) and 18 outdoor (1,000-l) tanks at 100 and 60 shrimp/m2, respectively. Shrimp were reared under clear (indoor) and green-water (outdoor) conditions for 72 days. For the study, six diets were formulated, three with the feeding effectors krill meal and wholes squid meal. Diets with and without feeding effectors were designated as ATMt and FPMt, respectively. For each diet group, one was designated as the basal diet (80) with a high inclusion of FPA and methionine levels above other diets. Remainder diets were identified as 70 and 60, diets formulated to meet 70% and 60%, respectively, of methionine requirements reported for penaeid shrimp. The attractiveness study consisted in the measurement of the feeding responses of L. vannamei using a double choice chamber (Y-maze apparatus). All experimental diets were confronted against each other 20 times each, allowing each diet to be tested 10 times in each side of the chamber. Diet attractiveness was measured visually through the animal feeding behavior categorized in accordance to the following responses: (1) time spent until detection; (2) times spent during orientation and locomotion to the food source, and (3) time spent for feeding. At harvest, under the indoor system, minimum and maximum shrimp body weight were achieved with diets ATMt(80) (16.19 ± 2.09 g) and FPMt(60) (17.30 ± 2.19 g). Comparatively, animals reared under green water achieved a body weight between 14.35 ± 2.53 g (FPMt(70)) and 15.46 ± 2.56 g (FPMt(60)). In clear water, inclusion of whole squid meal and krill meal in ATMt diets did not promote a greater shrimp body weight at harvest compared to FPMt diets. Under these conditions, L. vannamei achieved a final survival above 90% in all treatments, except for FPMt(60) (i.e., 61.4 ± 13.6%). Mean shrimp survival in green water conditions was 83.8 ± 9.6%, lower than under the indoor Andriola-Neto, F.F. Redução no uso de farinha de peixe em dietas suplementadas... xviii system. Shrimp yield indoors was twice higher than outdoors. In both indoor and outdoor systems, inclusion of feeding effectors in ATMt diets did not promote a higher feed intake for L. vannamei compared to FPMt diets. A total of 338 shrimp behavioral observations were conducted to evaluate diet attractiveness. There was no statistical difference between ATMt diets for the time spent until detection, orientation and locomotion and feeding. Diets FPMt exhibited differences for the time spent in orientation and locomotion and feeding. No statistical differences were observed for shrimp behavioral responses when ATMt and FPMt diets with similar methionine levels were compared individually. The present study indicated that the rearing system had an influence over the growth responses of L. vannamei. Shrimp farmed under clear-water (indoor) displayed better growth responses compared to those reared under green-water (outdoor). Whole squid meal and krill meal did not enhance growth performance and feeding responses of L. vannamei. However, the use of feeding effectors allowed balancing these parameters in diets containing similar formulated levels of methionine, for both rearing systems. The different levels of formulated methionine (60, 70 and 80% shrimp requirements) only influenced shrimp performance when these were fed with diets without feeding effectors.