Largehead hairtail, Trichiurus japonicus, are one of the important commercial fish species in East Asia such as Korea, China, and Japan. Jeju Island, located in the southernmost part of Korea, has abundant food resources and a warm water temperature, forming a major fishery ground for largehead hairtail. However, due to overfishing, largehead hairtail resources have decreased by more than 50% compared to the 2000s in Korea. The fish reproductive cycle provides basic knowledge for such as establishing a closed season to prevent overfishing and next year resource management. In this study, we were monitoring maturity level of largehead hairtail caught in Jeju Island during the main spawning season.
The fish samples were purchased at fish market in harbor located in Jeju Island. The maturity was classified according to total length and anal length. The monthly maturity level investigated from April to August. The maturity level was determined based on the gonadosomatic index (GSI), hepatosomatic index (HSI), condition factor (K) and absolute fecundity.
As a result, the mature female largehead hairtail maintained a higher maturity level from April than immature individuals and they began to mature more rapidly from May, showing the highest fecundity. The maturity level of mature females was maintained at a higher level until August. Therefore, some individuals had already finished spawning in August. In the case of immature females and males, they have a low maturity level until July. However, some immature females have ovulated eggs in the abdomen and most of the immature males showed high HIS levels in August.
These monitoring results suggested that mature females continue to participate during the spawning season, and they are expected to spawn eggs once or several times. The immature female and male maturation started in August, however, in some cases, fast maturing individuals may participate in spawning quickly. In the future, continuous this monitoring, we will get more detailed information about the maturity level and spawning patterns of largehead hairtail. Furthermore, we will be able to understand through this information their life history more deeply.