STUDY ON MORPHOLOGICAL DEVELOPMENT OF FALL CHUM SALMON (ONCORHYNCHUS KETA) OTOLITHS IN HEILONGJIANG RIVER

The salmons (Oncorhynchus) lives in cold waters, and inhabits in the North Pacific Ocean and its coastal water. The salmon is anadromous reproduction and migrates from sea to river in its breeding season. It is an extremely valuable and economic species in our country. Due to over fishing, habitat destruction, pollution, climate change and other reasons, the resource of fall chum salmon (Oncorhynchus keta) is currently facing such a situation of shrinking distribution, decreasing populations, and becoming endangered. Otoliths can record the early history of salmon fish lives in environment. In this study, through the artificial breeding experiment of reproductive groups in Heilongjiang River of China, the variation of fall chum salmon otolith was investigated in different developmental stages. Based on the result of investigation, we established some relationship between the early growth of fish and otolith morphology, and then we researched the early growth and development of individual characteristics and population replenishment process by analyzing the otolith morphology and microstructure. The result showed that the otolith of embryos, post-embryonic larvae, juvenile and young fish (included two years fish) grew gradually with the growth and development of fish body, and the shape and contracture of otolith was evolved gradually to that of adult otolith. The morphology of sagittae and lapillus in the breeding stock of chum salmon were identical regardless of age and sex. The shape of sagittae likes pear’s outline and its size and weight were about 3 mm×5 mm×1 mm and 9 mg respectively. The structure of daily and annual rings in otolith could be seen in microscope. The daily ring was emerged about five days after egg eyed, and the characteristic of the daily ring was proved by artificial marking. The otolith of two years fish had appeared edge growing area, which formed annual rings. The increment of the sagittae was significantly correlative with the growth of fish fork length (SL = 21.574OL?7.005, R2 = 0.9926). The results showed the relationship between individual growth and the evolution of the otolith’s micro-structure. By studying the early life stages of chum salmon, we could reveal the early stock replenishment process of salmon and provide a theoretical basis for the measurement of reasonable protection, restoration and artificial releasing.