Food and feeding of Siganus lineatus from waters around Northern Sri Lanka

Siganus lineatus (Cuvier and Valenciennes), is a marine fish which inhabits coastal areas and brackish water bodies in Sri Lanka. This is found in the tropical parts of the Indian and Pacific oceans. Stomach contents of fish ranging from 2.4 cm to 25.5 cm in standard length, collected from twelve stations along the Northern coast, Thondaimannar and Jaffna lagoons were examined. Analysis of stomach contents revealed that S. lineatus is purely a herbivore feeding on twelve genera of diatoms, four genera of blue-green algae, six genera of green algae, nine genera of red algae, a brown alga Dictyota and an angiosperm - Thallasia, of which the diatoms predominated. The major components were Licmophora, Gomphonema, Navicula, Oscillatoria, Cladophora, Chaetomorpha, Gracilaria and Laurencia. Thallasia pre-dominated all the other genera except the diatoms. When the variation in the feeding habits with the size of the fish was analysed by placing the fish in 3 cm length classes, no significant difference in the food was found. The analysis of stomach fullness of the specimens collected during day and night indicated preference to feed during night. An apparent indication of stomach fullness with increase in size of fish has been detected. Siganus lineatus is herbivorous in nature.