Synchronization to light and mealtime of daily rhythms of locomotor activity, plasma glucose and digestive enzymes in the Nile tilapia (Oreochromis niloticus).

The light-dark cycle and feeding can be the most important factors acting as synchronizers of biological rhythms. In this research we aimed to evaluate synchronization to feeding schedule of daily rhythms of locomotor activity and digestive enzymes of tilapia. For that purpose, 120 tilapias (65.0±0.6g) were distributed in 12 tanks (10 fish per tank) and divided into two groups. One group was fed once a day at 11:00h (zeitgeber time, ZT6) (ML group) and the other group was fed at 23:00h (ZT18) (MD group). The fish were anesthetized to collect samples of blood, stomach and midgut at 4-hour intervals over a period of 24h. Fish fed at ML showed a diurnal locomotor activity (74% of the total daily activity occurring during the light phase) and synchronization to the feeding schedule, as this group showed anticipation to the feeding time. Fish fed at MD showed a disruption in the pattern of locomotor activity and became less diurnal (59%). Alkaline protease activity in the midgut showed daily rhythm with the achrophase at the beginning of the dark phase in both ML and MD groups. Acid protease and amylase did not show significant daily rhythms. Plasma glucose showed a daily rhythm with the achrophase shifted by 12h in the ML and MD groups. These results revealed that the feeding time and light cycle synchronize differently the daily rhythms of behavior, digestive physiology and plasma metabolites in the Nile tilapia, which indicate the plasticity of the circadian system and its synchronizers.

Influência da dieta suplementada com óleo de soja na composição centesimal e perfil lipídico de tilápias do Nilo (Oreochromis niloticus) / Effect of dietary regime supplemented with soybean oil on the lipid profile and chemical composition of Nile tilapia (Oreochromis niloticus)

A dieta exerce efeito pronunciado na composição das carcaças de peixes. Neste trabalho, foi avaliada a qualidade nutricional da fração lipídica do tecido muscular de tilápias do Nilo (Oreochromis niloticus) submetidas a dietas com diferentes teores de óleo de soja (OS). Os peixes foram alimentados por 21 dias com ração contendo 5,98% de lipídios totais (LT) oriundos de ração comercial, sem adição de óleo de soja(A), dieta com adição de 2% (B) e 4% de óleo de soja (C). Não houve diferenças significativas (p > 0,05)entre os teores de umidade, cinzas, proteína bruta e LT (0,98% a 1,08%) dos tecidos musculares resultantes dos tratamentos. Foram separados e identificados até 25 ácidos graxos, com diferença significativa (p <0,05) na maioria deles, dependendo da dieta. Os majoritários em ordem decrescente foram: 16:0, 18:1n9,18:2n6, 18:0, 20:4n6 e 22:5n6, independentemente do tratamento. A adição de OS na ração comercial mostrou perspectivas de promover o crescimento dos animais, sem afetar a composição centesimal e a qualidade nutricional da fração lipídica do tecido, em função dos altos teores de poli-insaturados, indicando ser uma matéria-prima satisfatória para incorporação parcial na ração.