Seasonal and length group based changes in the development of gonad and light organ (LO) were studied in pug-nose ponyfish, Secutor insidiator. The male fishes having larger light organs compared to conspecific females belonging to the same length group.Gonadosomatic Index and Percentage Light organ Weight (PLW) were used to find out the possible synchronization in the gonad and light organ enlargement in both sexes. In males and females mean GSI showed marked increase two times of the year. A prolonged breeding period from June to September with peak in August and another short period from February to March with peak in March. Seasonal changes in the mean PLW in males showed the same trend as that of GSI, whereas the mean PLW in females remained almost same throughout the year. A significant positive correlation was observed between GSI and PLW in males but not in females; it can be suggested that gonad and light organ development correlation is seen in males during the breeding season irrespective of the length of the fish whereas, LO remained the almost same size in all sexually mature females irrespective of the length of the fish and breeding seasons. The result suggested the possible role of bioluminescence in reproduction of this silverbelly species as reported for many other species.

Secutor insidiator, light organ, Gonadosomatic index, percentage light organ weight, bioluminescence.