Trophic Level, Food Preference and Feeding Ecology of Rachycentron canadum (Linnaeus. 1766), in Hormuzgun province Waters (Northern Persian Gulf and Oman Sea)

Abstract

The aim of this study was to assess the ecological factors associated with feeding by Rachycentron canadum (cobia) in the waters of Hormuzgan Province, Iran. Specimens were collected seasonally from Sep. 2014–Sep. 2015 from the Ferdows-1 survey ship and from landing areas in the city of Bandar Abbas. A total of 577 cobia were collected (340 male, 237 female) (20–161 cm Total length). Our results provide the first estimates of trophic level (TL) (4.4 ± 0.76, mean ± SE), consumption per biomass (Q/B) (6.13), and aspect ratio of the caudal fin (ARc.f) (3.1) for R. canadum in the Hormuzgan Province. We also found that osteichthies made up more than 80 percent of the relative importance of particular prey (IRI %), indicating that R. canadum primarily preys on these species. The immature group tended to feed on shrimp, crabs, and mollusks, and predominance of shrimp, crabs, and mollusks was also observed among the stomach contents of cobia ranging from 20–40(c.m). Hierarchical clustering revealed that the frequencies of different types of prey could be used to divide the length classes into three groups. A compare means test comparing the immature and mature groups and a one-way analysis of variance (ANOVA) comparing length classes revealed that the immature group and the 20-40 length class tended to feed on shrimp, crabs, and mollusks. Also, we found that males generally fed more than females in all seasons and that R.canadum had an average dietary intake. Our results suggest that the removal of top predators, such as cobia, could disturb the entire ecosystem because they play a fundamental role in maintaining a balance in the populations of their prey. Also, because diet is important for aquaculture, the findings of this study can be used to prepare a food formulation for cobia that resembles the native diet.