Race Separation of Deep Sea Smelt of Japan Sea

Abstract

The spawning season of the deep sea smelt of Japan Sea was found to be very long, extending to several months. Hence it is believed that two or more races could be spawning one after the other. On the basis of otolith patterns this fish population could be separated into two major groups. The developmental pattern of the otolith of the deep sea smelt has been shown in a model else where. Linear discriminant function analysis of seven meristic characters showed a distinct variation between the groups. Tests showed that the yearly variation of the meristic characters were not significant.Deep sea smelt, Glossonodon semifasciatus, as the name implied is a bottom feeding, slender, long fish living at a depth of about 100 to 150 meters. It is an important con tributor to the Danish seine fishery of Japan Sea. The fishing season of this fish falls on its spawning season, which extends from September to March. The spawning season being so long it is believed that two or more races would be spawning one after the other. This behavior has been observed in herring populations by several workers. On the basis of otolith pattern deep sea smelt population could be separated into two major groups. According to the model constructed by SINODA and JAYASINGHE10) hypothesizing the developmental pattern of the otolith of this fish, early spawners will have bigger hya line nucleii and narrower first growth zones, while late spawners may have smaller nucleii and wider first growth zones. The growth rates of the two groups showed a consider able difference. The growth constants calculated from VON BERTALANFFY'S growth curves for the two groups gave 0.5137 and 0.3682 year-1 for winter-early spring spawners and autumn spawners respectively. This may be due to varied metabolic rates under different environmental conditions or due to feeding competition in the community.The growth curves of the two groups shown in Fig. 1, seems to give good envidence in confirmation of the assumptions on which the model represents the otolith formation.There is a shift of about five months in the origin of growth curve of the autumn-early winter spawners from that of the spring spawners. This clearly shows that birth times of the two groups are different to each other. As a method of separating these two populations discrimi nant analysis was employed. Materials and MethodsSamples of both juvenile and adult deep sea smelt were collected from the commercial