Ontogenetic diet shifts and feeding dynamics of Trichiurus japonicus Temminck & Schlegel, 1844, off Guishan Island, Southern East China Sea

Abstract

Trichiurus japonicus Temminck & Schlegel, 1844, is one of the most ecologically and economically important fish species in the waters of southern East China Sea. Species caught by trawlers operating in the surrounding waters of Guishan Island, southern East China Sea were collected regularly from March 2018 to February 2019. The stomachs of 434 hairtails ranging in total length (TL) from 100 to 1090 mm were analyzed to study their feeding habits. Diet composition and seasonal changes in prey items were analyzed over 12 months (2018–2019) to detect any feeding shifts in prey items. Feeding indices, namely Index of Relative Importance (%IRI), Gastro-somatic Index (GaSI), Empty Stomach Ratio (ESR), and Stomach Fullness Index (SFI), were calculated to determine the feeding habits, seasonal changes, and ontogenetic shifts in prey items. ESR values differed significantly across hairtail size groups. However, no significant variations were found in ESR values between the sexes and season. The diet of T. japonicus comprised fish (80.07%), shrimps (13.89%), cephalopods (0.61%), and miscellaneous items (5.43%). Benthosema pterotum was the most common prey item during the research period, followed by Myctophidae spp and Sergia lucens. The vacuity index (VI) of T. japonicus was 29.26 percent, indicating that it is a carnivore with a relatively edacious. An unidentified teleost, as well as shrimp remains, was observed in the form and was grouped as miscellaneous items. Juveniles of Trichiurus sp. were noticed occasionally in the gut, indicating the cannibalistic behavior of T. japonicus.