RESUMO
The daily variations of temperature are one of the main synchronizers of the circadian rhythms. In addition, water temperature influences the embryonic and larval development of fish and directly affects their metabolic processes. The application of thermocycles to fish larvae has been reported to improve growth and the maturation of the digestive system, but their effects on metabolism are poorly understood. The aim of the present study was to evaluate the effect of two different temperature regimes, cycling versus constant, on the daily rhythms of metabolic factors of Nile tilapia (Oreochromis niloticus) larvae. For this purpose, fertilized eggs were divided into two groups: one reared in a 31 °C:25 °C day:night thermocycle (TCY) and another group maintained in a constant 28 °C temperature (CTE). The photoperiod was set to a 12:12 h light/dark cycle. Samples were collected every 4 h during a 24-h cycle on days 4, 8 and 13 post fertilization (dpf). The expression levels of alanine aminotransferase (alt), aspartate aminotransferase (ast), malic enzyme, glucose-6-phosphate dehydrogenase (g6pd), phosphofructokinase (pfk) and pyruvate kinase (pk) were analyzed by qPCR. Results showed that, in 13 dpf animals, most of the genes analyzed (alt, ast, malic, g6pd and pfk) showed daily rhythms in TCY, but not in the group kept at constant temperature, with most acrophases detected during the feeding period. An increase in nutrient metabolism around feeding time can improve food utilization and thus increase larval performance. Therefore, the use of thermocycles is recommended for tilapia larviculture.
RESUMO
The experiment carried out at National Center for Research in Tropical Fish Pirassununga, SP, aiming to determine the effect of the ration processing on the apparent digestibility coefficients of the ingredients for the piau (L. elongatus). A total of 600 males of piau were utilized, allotted into six ponds of 300L. The applied treatments were: grinder processed ration, pelleting ration and extruded ration, utilizing rations with 32% crude protein and 3400 Kcal DE.Kg-1. The experiment was in a randomized blocks design with three treatments, three blocks and two replicates. The data were submitted to variance analysis by the SAEG computational package and the means of the treatments compared by SNK test (5% of significance). The results showed that there were significant differences among the digestibility coefficients of both protein and energy for the pelleted and extrused rations (P<0.05). The results showed no statistical differences for the apparent digestibility coefficient of the dry matter (P>0.05).
O experimento foi realizado no Centro Nacional de Pesquisa de Peixes Tropicais de Pirassununga, SP, objetivando-se determinar o efeito do processamento da ração sobre os coeficientes de digestibilidade aparente dos ingredientes para o piau (L. elongatus). Foram utilizados 600 machos de piau, distribuídos em seis tanques de 300 L. Os tratamentos aplicados foram: ração farelada, ração peletizada e ração extrusada, formuladas com 32% de PB e 3400 Kcal ED/Kg. O delineamento experimental foi em blocos casualizados, com três tratamentos, três blocos e duas repetições por tratamento. As análises estatísticas foram realizadas pelo SAEG, com as médias comparadas pelo teste SNK (5%). Houve diferenças entre os coeficientes de digestibilidade da proteína bruta e energia para as rações peletizada e extusada (P<0,05). A digestibilidade da matéria seca não diferiu mediante os processamentos avaliados (P>0,05).
