Chemical sensitivity of juvenile brown-marbled grouper, Epinephelus fuscoguttatus to betaine and amino acids, and their preference for aquafeed development

Lim, Leong Seng (2015) Chemical sensitivity of juvenile brown-marbled grouper, Epinephelus fuscoguttatus to betaine and amino acids, and their preference for aquafeed development. Doctoral thesis, Universiti Malaysia Sabah.

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Grouper aquaculture is expanding but most grouper farmers are challenged by high cost of feed input due to the dependency on the expensive fish meal. Soybean meal (SSM) has high potential to replace fish meal but at high inclusion levels, diets palatability is affected. The use of suitable feeding stimulant (via gustation) or attractant (via olfaction) in non-fish meal based diets might be able to increase feed intake. Amino acids and betaine are commonly used as feeding stimulant and attractant in aquaculture feeds. Unfortunately, little is known about the specific response of grouper to these substances. The present study aimed to investigate the chemical responses in the grouper (Epinephelus fuscoguttatus) to feeding stimulant and attractant and evaluate its potential to promote the intake on SSM based diets through an electrophysiology (Experiment 1), two behavioural (Experiments 2 & 3) and a feeding experiments (experiment 4). In experiment 1, cysteine was determined as the most sensitive amino acid to the olfaction of grouper, followed by lysine and arginine at the concentration of 10⁻³ M through electro-olfactogram analysis. The threshold level of cysteine was also determined at 10⁻⁵M. experiment 2 was carried out to confirm the results of Experiment 1 through behavioural study. Cysteine yielded the highest frequency in both the Swimming and food searching activities, indicating its suitability as food attractant. In this experiment, It was realized that olfaction may not playa very critical role in cultured grouper because they are visual feeder and food are always provided by the farmers. Besides, the decision in food ingestion is mediated by gustation. Consequently, identification of feeding stimulant instead of attractant is more appropriate for the cultured grouper. Therefore, Experiment 3 was conducted to study the taste effect of betaine and the preference for amino acids in tiger grouper using video recording and agar gel pellet as the delivery medium. It was determined that betaine functions best as a feed enhancer in grouper. Betaine itself has low palatability but it enhanced the flavour of the amino acids mixture (also low in palatability) and improved the intake of the agar gel pellet by the fish. Interestingly, only small amount of betaine was required to enhance the flavour of the amino acids mixture (betaine: amino acids mixture 1:4). Among all the amino acids tested, only amino acid A was properly ingested by the fish. The fish acceptance for the amino acid A did not change with growth. In fact, the taste sensitivity for amino add A improved with the size of fish. In experiment 4, an 8- week feeding trial was conducted to evaluate the potential of betaine and mixture of the selected amino acids to promote intake of SSM-based diets in the grouper. Although the best performance was achieved by the fish fed control diet, supplementation of betaine and the amino acids mixture improved the feed Intake and growth in fish fed SSM-based diets. The optimum supplementation level of betaine was also determined at 1.0% based on the higher feed intake and fish growth in this treatment. In conclusion, narrow chemical sensitivity to spectrum of amino acids In the grouper is observed. The findings of the study suggest that the issue with low palatability in SBM-based diets in grouper aquaculture can be solved by the use of species-specific attractant and stimulant.

Item Type: Thesis (Doctoral)
Keyword: chemical responses, grouper, feeding stimulant, diet, feeding experiments, electrophysiology, behavioural
Subjects: S Agriculture > SH Aquaculture. Fisheries. Angling
Department: INSTITUTE > Borneo Marine Research Institute
Date Deposited: 24 Oct 2017 11:39
Last Modified: 24 Oct 2017 11:39

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