Gustatory preferences of purple mud crab (Scylla tranquebarica) towards formulated diets made of various marine protein sources

Mud crabs are a valuable aquaculture species, yet no commercially formulated feed is available. The slow progress in feed development is to some extent due to their poor acceptance of formulated diets. Besides attractability, ensuring feed palatability is essential for developing a species-specific diet too, with protein sources playing a key role in this process. The present study examined the gustatory preference (palatability) of Scylla tranquebarica for pelleted diet formulated with three different marine protein sources: fish meal (FM), sergestid shrimp meal (SSM), and squid meal (SQM). From these protein sources, six isoproteic (45 % crude protein) and isolipidic (10 % crude lipid) diets were formulated and designated as FM100 (100 % fish meal protein), SQM100, SSM100, FM50SQM50 (50 % fish meal and 50 % squid meal proteins), FM50SSM50, and SSM50SQM50. These dietary formulations were designated to evaluate the palatability of individual protein sources as well as their combinations. Twenty wild S. tranquebarica were successfully acclimated and used in this experiment. The gustatory preference of S. tranquebarica for the experimental diets was assessed by observing and evaluating their feeding response to each diet. Their feeding responses were categorised into discrete levels and evaluated using a scoring method: a score of 0 indicated no response, 1 indicated tasting, and 2 indicated ingestion The mean feeding score for each dietary treatment was subsequently calculated as the representative data. All feeding score data were statistically analysed using a non-parametric repeated measures Friedman test, followed by a post hoc Conover test with Bonferroni correction. Statistical significance was accepted at p < 0.05. Among the six diets, SQM100 attained the highest mean feeding score (1.65 out of 2.00), followed by SSM50SQM50 (1.60), SSM100 (1.45), FM50SQM50 (1.25), FM50SSM50 (1.15), and FM100 (0.70). The mean score of FM100 was significantly lower (p < 0.05) than all other diets, while no significant differences (p > 0.05) were observed among the remaining five diets. Additionally, SQM100 and SSM100 were consumed by 65 % and 55 % of S. tranquebarica , respectively, whereas none consumed FM100, demonstrating a clear difference in dietary preference. By replacing 50 % of fish meal protein with squid or sergestid shrimp meal, the ingestion rate increased to 35 % for FM50SSM50 and 40 % for FM50SQM50, significantly enhanced the diet palatability. In conclusion, squid and sergestid shrimp meals are highly palatable protein sources for S. tranquebarica and can serve as effective substitutes for fish meal in their diet formulations.