Significant variations in the number of white and red blood cells, haematocrit and haemoglobin were found throughout the year in sexually mature male and female tench Tinca tinca. In general, the lowest values were observed during autumn-winter and the highest during summer, with males exhibiting higher values than females. Plasma glucose, cholesterol and triglycerides were lower during the winter than during the summer-autumn seasons in both sexes. Gonadosomatic and hepato-somatic indices were inversely correlated in female tench throughout the year. Seasonal patterns in liver metabolic resources were very similar for both sexes. For males and females, liver glycogen and proteins increased during the autumn, whereas the liver stored lipid during spring. Dorsal muscle mainly deposited glycogen, whereas lipid was mainly stored in the ventral muscle. Relations between seasonal changes in environmental factors, such as feeding and temperature are discussed.
The effects of short-term food deprivation (7 days) and refeeding (2 days) on different biochemical and neuroendocrine parameters were studied in tench. A 7-days fast resulted in a significant reduction of plasma glucose and glycogen hepatic content, supporting the key role of liver glycogen as energy depot for being consumed during fasting. The rapid recovery of normal values of blood glucose and glycogen stores by refeeding indicates a rapid replenishment of liver glycogen stores. The short-term starvation decreased circulating thyroid hormones (both T3 and T4) and T4 release from thyroid, supporting an interaction between nutritional state and thyroid function in tench. All these metabolic and hormonal changes were partial or totally reversed under refeeding conditions. An increase in hypothalamic content of norepinephrine and dopamine was found in fasted fish. This result might be a consequence of stress induced by starvation.
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