The effect of dietary indispensable amino acid imbalances on feed intake: Is there a sensing of deficiency and neural signaling present in fish?

Sammendrag

Most studies on amino acid imbalance and dietary selectivity in fish have been conducted using mammalian models. In rats, amino acid deficiencies cause a rapid, within minutes, decrease in food intake. In comparison, teleost fish have no aversion to indispensable amino acid-devoid diets, although possible taste aversion was not distinguished from neurological feedback. Therefore, it remains to be answered if amino acid attractant(s) can override neurological responses to amino acid deficiency in the diet. We report here for the first time the effects of dietary amino acid imbalances on the diet intake, and survival and growth response in a juvenile cichlid, midas (Amphilophus citrinellum). In the first experiment, a protein-based, a free amino acid-based diet (Free AA) and two indispensable amino acid (IDAA) devoid diets were tested. Fish responded initially by a decreased feed intake, but two weeks into the experiment, a significantly increased intake of the amino acid imbalanced diets was observed. In the second experiment, free amino acid imbalanced diets were offered to the fish using four different feeding strategy/treatments. These strategies were based on frequency of feeding imbalanced diets that changed from “different diet in every meal” to “different diet each other day”. However, every two days the amount of IAA provided to all groups was identical. Fish in all feeding treatments increased their body weight significantly, but their final weights decreased linearly with lower frequency of complimentary diet provision. There were significant differences in diet utilization when expressed as feed conversions. However, the most significant results demonstrated that weight gains calculated on the weekly basis improved significantly in all imbalanced/complimentary diet treatment groups. It is hypothesized that due to their high tolerance to amino acid imbalances, fish are the ideal model to reexamine metabolic responses to dietary disproportions of amino acids.