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Fructose 1,6 bisphosphatase activity in liver and gonads of sea bass (Dicentrarchus labrax). Influence of diet composition and stage of the reproductive cycle

Abstract:

The fructose 1,6 biphosphatase (FBPase) activity was measured in the liver and gonads of broodstock sea bass that were fed three experimental diets over the reproductive cycle. Enzyme activity was measured at the pre-spawning (November), spawning (February) and post-spawning (May) periods. Additionally, some biometric indices were calculated at these three times. The different diets, one with standard composition (51% protein, 13% lipid, 10% digestible carbohydrates), one with a high-carbohydrate content (32% protein, 13% lipid, 32% digestible carbohydrates) and one deficient in ω3 essential fatty acids (51% protein, 13% lipid, 10% digestible carbohydrates), had similar affects on growth and gonad development, as deduced from the similar weight, condition factor, hepatosomatic index, gonadosomatic index and liposomatic index over the reproductive cycle. FBPase activity was detected at all times in the liver of both sexes, and in the ovaries but not in the testes. In general, females showed greater liver activity than males, especially at spawning time. During post-spawning, FBPase activity fell in tissues of both sexes. Enzyme activity was also affected, mostly in the liver, by the different types of feed; hepatic activity in fish fed the high-carbohydrate diet fell during the spawning and post-spawning periods, though at a different level for each sex. The diet deficient in ω3 EFA presented the lowest FBPase activity, compared with the other diets, in females during the spawning period; there was very little change in males or females over the reproductive cycle. The results showed that the highest gluconeogenic activity in sea bass broodstock occurred at the spawning time and the females had larger glucose requirements than males over the reproductive cycle, as demon-strated by the absence of FBPase activity in testes. This work also confirmed the adaptative capacity of this enzyme to different nutritional and physiological conditions.