| Resumo: |
Considering the need to help the Cuban shrimp culture industry remain profitable, and the impact that feeding has on production costs, a research series was designed to evaluate new formulations that improve white shrimp Litopenaeus schmitti growth and reduce feeding costs. Five completely randomized experiments with 3 replicates per treatment were conducted. Juveniles (0.2-0.5 g) from the experimental farm were used. Trials were conducted at the Centro de Obtención y Cría de Larvas de Santa Cruz del Sur, Camaguey, and the Complejo Camaronero de Tunas de Zaza, Sancti Spiritus. In the first trial, 40-l plastic experimental units with 10 shrimp/unit were used to test the response of L. schmitti to the partial and total substitution (46, 59, 75, 88 y 100%) of fish meal by soybean meal, using as control the formulation fed at commercial farms (S46), and defining the optimum level of substitution. After 52 days, results showed that there were no significant differences in final weight (Fw), food conversion rate (FCR) and protein efficiency (PE) when substituting up to 75% fish meal. The broken line analysis showed that 76.5 ± 2% fish meal substitution represents the optimum level, in diets where fish meal and soybean meal are the only protein sources, and there is no natural productivity in the water. A second trail was conducted in 250 m2 fertilized earthen ponds, stocked at 10 shrimp/m2. Three formulations were tested: S46 (control), S59 and S70 that substituted 70% of the fish meal. Results showed that S70 significantly improves Fw (7.88 g) when compared with S46 (7.00 g). FCR tended to diminish with increased fish meal replacement (2.16, 1.92, 1.89). However, differences were not significant between treatments. Survival was over 80% in all cases. Using S70 resulted in a feed (FC) and production costs (PC) reduction of, respectively, 8 and 10%. In the third trial, S70 was used as control. This diet contained a high level of soy meal, which could cause palatability and atractability problems. The ability of 5% fish meal replacement by shrimp-head meal (CC5%) or S70 pellet spraying with 0.5% fish oil (RAHT0.5%) as attractants, exciters or stimulants was tested. A second evaluation in this trial was conducted in ponds. Results showed that the additives work as attractants, exciters and stimulants with respect to the control. Significant increases in Fw (16, 18%), and reductions in FCR (25%) and PC (28%) were obtained. Survival increased significantly with values of 81, 90 and 92% for S70, CC5% and RAHT0.5%. Even though diets were isoproteic, protein was used more efficiently in the presence of additives. A fourth experiment tested the use of astaxanthin, a carotenoid pigment that may positively affect shrimp growth. Oil-sprayed S70 was used as control. Diets that included 25, 50, 75 or 100 mg/kg astaxanthin were tested. After 45 days, diets with an astaxanthin concentration at least 50 mg/kg resulted in higher Fw (33-36%) and lower FCR (37%), which reflect better diet assimilation. Survival was over 90% for all treatments. A dose-response analysis using a logistic curve suggested that the astaxanthin level that optimizes the productive response may be found between 25 and 50 mg/kg astaxanthin inclusion. The fifth experiment was conducted in 1 m2 enclosures inside a 0.1 ha fertilized pond. S46 was used as control. Diets S70, S70 with 5% shrimp-head meal (S70CC5), S70 with 50 mg/kg astaxanthin (S70A50) and S70 with both shrimp-head meal and astaxanthin (S70A50CC5) were tested. All diets were sprayed with 0.5% fish oil, except S46. Each diet was tested at three densities (10, 15 y 20 shrimp/m2). Diet S70A50CC5 was nutritionally more efficient than the control (S46). This diet allowed density to increase to 20 shrimp/m2, with growth rate increases of 43%, and reductions of 49% in FCA. This significantly reduced CP (54-66%), depending on density. Higher survival values (99%) occurred when feeding S70A50CC5 or S70A50. Lower Fw an FCRs were observed at 20 shrimp/m2 for diets S46 and S70.
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