Trophic ecology and diet of the deep-sea penaeid shrimp Metapenaeopsis andamanensis (Wood-Mason in Wood-Mason and Alcock, 1891) by fatty acid signatures and stomach content analysis.

Metapenaeopsis andamanensis, a deep-water penaeid shrimp, plays a significant ecological role in the deep-sea food web. However, studies on its feeding ecology and trophic relationships in the tropical region remain limited. This study aimed to investigate the diet composition of M. andamanensis from the southwest coast of India, focusing on intrinsic factors (size, sex, maturity) and extrinsic factors (seasons), as well as the fatty acid profile. Our findings revealed that M. andamanensis is an active feeder, with females exhibiting higher feeding intensity than males, while immature individuals of both sexes showed minimal feeding activity. Additionally, females displayed a more pronounced carnivorous feeding behavior compared to males. Gut somatic index ranged between 1.1 and 1.42. Feeding conditions varied significantly with seasons, maturity stages, and onto genetic classes. The primary diet components comprised detritus, foraminifera, and crustaceans, followed by gastropods and fish. Statistical analysis using PERMANOVA indicated significant differences in diet components between sexes and seasons (p < 0.05), sexes and size (p < 0.1), and sexes and maturity stages (p < 0.05). Notably, the percentage composition of diet components exhibited substantial variation with seasons, sex, ontogenetic classes, and maturity stages. Fatty acid analysis revealed an omnivorous-carnivorous feeding strategy of M. andamanensis, characterized by high proportions of essential fatty acids such as 20:5n-3, 22:6n-3, and 18:1n-9, indicating bentho-pelagic feeding activity. The shrimp exhibited notable levels of palmitic acid, oleic acid, EPA, and DHA, which are nutritionally valuable. Seasonal variations in fatty acid profiles were associated with the availability of different food sources. Principal component analysis (PCA) performed on the fatty acid profiles explained 72.4% of the total cumulative variance using the first two dimensions, highlighting the distinct dietary patterns of M. andamanensis based on its stomach contents.