Uso do farelo de Ulva fasciata como ingrediente em dietas para larvas de tilápia-do-Nilo Oreochromis niloticus.

Abstract

Aquaculture of tropical fish usually present high mortality rates in the larviculture phase, as the larvae have anatomical and physiological structures still in formation. The management and adoption of inappropriate technology can compromise the yield of the other phases of the cycle, reducing productivity and resulting in a lower number of juveniles. In addition, an ineffective larviculture tends to generate animals of low quality, with lower growth rates and more susceptible to diseases. On the other hand, adequate food management with balanced diets can lead to an improvement in the production, in qualitative and quantitative terms. Thus, the present study aimed to evaluate the effects of the seaweed meal Ulva fasciata as an ingredient in formulated diets during larviculture of Nile tilapia Oreochromis niloticus and, subsequently, to verify the survival and responses blood pressure of animals when subjected to stress management, ie. air exposure and osmotic shock. The experiment was divided into two phases (I and II), totaling 75 days. The study was carried out in a completely randomized design, with six treatments, inclusion levels of U. fasciata meal: 0, 2.5%, 5%, 7.5%, 10% and 12.5%. At the end of both phases there was no statistical difference for survival. At the end of Phase 1 (first 30 days of exogenous feeding), the increase in the U. fasciata meal levels’ resulted in a decreasing in larval performance. In Phase 2, there was no statistical difference for the performance parameters and the condition factor; with the exception of Specific growth rate (SGR), which was higher in juveniles fed diets containing 7.5 to 12.5% of U. fasciata meal compared to treatments that received diets containing 0 and 2.5%. Diets containing the highest levels of U. fasciata provided the highest levels of blood glucose compared to the other treatments. In the stress tests, the juveniles showed an increase in glucose levels shortly after the stress, and these levels returned to baseline values 24h after the tests. 5% of U. fasciata meal led to a smaller increase in blood glucose level after air exposure. Still, mortality was higher after 96 h in the treatment in which the fish received 12.5% of U. fasciata meal. The body protein and mineral matter were similar between treatments. Moisture and lipids were different and inversely proportional between treatments. Considering Phases 1 and 2 of the experiment, 2.5% of U. fasciata meal in dietary formulation can be recommended, without prejudice to performance and with no changes in blood glucose levels and a good response to the air stress challenge. Higher inclusion levels should be further evaluated in the future, as there were indications of a possible modulation of the glycemic response to the stressful situation.