An international team of researchers from Brazil and Portugal examined the addition of supplemental taurine and methionine to support the use of a plant-based diet for the production of meagre (Argyrosomus regius). The group published its work in the journal Aquaculture.
“[The] present study aimed to evaluate the potential of methionine and taurine supplementation as a nutritional strategy to mitigate growth performance reduction caused by low-fishmeal diets for juvenile meagre,” the researchers said. “Therefore, the effect of taurine and methionine supplementation to a practical plant protein-based diet on growth performance, feed efficiency, whole body composition, and intermediary metabolic enzymes activities was evaluated.”
The research team found that adding the dietary taurine boosted both growth and feed use, however, there was no influence seen from either level of methionine supplementation.
“Dietary methionine supplementation was inefficient to overcome the decreased taurine level in plant-based diets and thus, taurine should be incorporated in plant protein-based diets, as an efficient nutritional strategy for the mitigation of growth limitations of meagre fed diets with high levels of plant feed ingredients,” the researchers said. “Moreover, as growth performance was not improved by increasing dietary methionine this suggests that under our experimental conditions meagre requirements are met with 7.5 g kg−1 dietary methionine.”
Why taurine and methionine supplementation?
Farmed fish may adapt to different feeds and several studies have focused on that plasticity to improve fish performance and nutrient use in aquaculture production, the researchers said. Reducing the use of fishmeal in diets is usually considered a way to cut costs and improve the sustainability of diets.
However, carnivorous fish continue to have a high protein requirement and only select ingredients can be used to provide an alternative feed ingredient, they said. Alternative ingredients need to have high protein levels, balanced amino acid profiles and high nutrient digestibility.
The use of plant-based proteins in the diets of carnivorous fish may shift their metabolic profile, including the ways they use protein and carbohydrates, they said. Adding crystalline amino acids may balance plant proteins and improve fish growth performance.
Methionine is an essential amino acid in fish diets, they said. Taurine is present in high levels in fishmeal but can be lacking in plant proteins.
The amino acid is involved in several physiological processes, the researchers said. Some fish have the ability to synthesize quantities of taurine from sulfur amino acids, however not all fish species have their needs met in that manner.
“The limited capacity to synthesize taurine in fish may impose a necessity of dietary supplementation with this amino acid when dietary intake is insufficient,” they said. “Recent work has indicated that taurine supplementation to plant protein-based diets is required to support increased growth in some fish species.”
Meagre is a marine carnivorous fish that is of interest to develop in farmed systems in the Mediterranean, the researchers said. It is a quick growing fish already accepted by consumers and has already seen an increase in global production.
“Even though meagre is presently farmed in the Mediterranean basin, its production has not yet reached its full potential and rearing trials are still very limited,” they said.
Methods and materials
Four trial isolipidic and isoproteic diets were designed for use during the 65-day feeding trial, the researchers said. The diets included 820g kg-1 of plant-based protein and 180g kg-1 of fishmeal with methionine at 7.5 or 10g kg-1 and with or without supplemental taurine at 10g kg-1.
Diets were pelleted for use, they said. Fish were assessed for growth performance and the activity of metabolic hepatic enzymes.
Fish were weighed at the beginning and end of the trial, sample fish were collected at the end of the trial to check whole-body composition, and whole fish, viscera were noted, they said. Hepatosomatic (HSI) and visceral indices (VI) were established and livers were collected for analysis.
No interaction was found between the use of methionine and taurine supplementation in regards to growth performance or feed intake, the researchers said. Methionine supplementation also had no effect. However, supplemental taurine improved all growth parameters.
“Results of the present study indicate that dietary supplementation of 10 g kg−1 of taurine, is an efficient nutritional strategy to mitigate growth limitations of meagre fed high levels of plant feed ingredients,” they said. “Increase of dietary methionine from 7.5 to 10 g kg−1 did not affect growth performance indicating that under the present experimental conditions dietary methionine needs of meagre were met with the lower dietary methionine tested.”
Fish getting the taurine-supplemented diets had a drop in daily feed intake, improved feed conversion and boosted protein efficiency ratios, they said. Lipid, energy and nitrogen retention also was higher.
“Dietary supplementation of taurine and methionine did not affect hepatosomatic indices, liver and whole body composition of meagre,” the researchers said. However, Alanine aminotransferase (ALT), aspartate aminotransferas (AST) and fructose-1, 6-bisphosphatase activities expanded with taurine supplementation but glutamate dehydrogenase (GDH) and glycolytic enzyme activity were not altered, they added.
Title: Taurine and methionine supplementation as a nutritional strategy for growth promotion of meagre (Argyrosomus regius) fed high plant protein diets
Authors: Lorena de Moura, Alexandre Diógenes, Daniel Campelo, Fernanda de Almeida, Pedro Pousão-Ferreira, Wilson Furuya, Aires Oliva-Teles, Helena Peres