Research on the differences of anadromous migratory distance between Coilia mystus and Coilia nasus based on the transfer process of body lipid

In order to figure out the possible reasons of the different migratory distances between Coilia mystus and C. nasus, we investigated the relationships between migration distance of the two sibling species and lipid reserves and transfer in this paper. Study of C. mystus showed that individuals arriving at spawning ground in May were significantly greater in body length than those in June, July and August. In particular, those larger-sized females with higher somatic lipid content arrived at spawning ground and spawned earlier than others. The average hepatosomatic index of C. mystus was relatively higher than that of C. nasus during the same development period, and the gonadosomatic index of C. mystus at stages Ⅲ and Ⅳ was about five times higher than that of C. nasus, indicating more energy centralized in ovary and easy-transferred organs of C. mystus during the spawning season. Although lipid content in muscle and liver of C. mystus was about one-third and half of that in C. nasus respectively during the same development period, C. mystus accumulated more lipid in ovary, a reproductive organ. Total trunk lipid in C. nasus decreased from 97.73% at phase Ⅱ to 91.02% at phase Ⅳ, compared to rapid decrease from 91.02% at phase Ⅱ to 34.69% at phase Ⅴ in C. mystus. The amount of lipid in hepatopancreas was relatively stable in both species, whereas the lipid proportion in ovary of C. mystus was obviously higher than that of C. nasus. The finding that C. mystus allocated most of the body lipid for gonadal development and rapidly consumed trunk lipid may represent the common characteristic of short-distance migratory fish.