Effect of salinity on the growth and feed conversion of rabbitfish, Siganus canaliculatus (Park, 1797), fed with seaweed (Gracilaria changii)

The low production of the rabbitfish Siganus canaliculatus and the high price fluctuations of the seaweed Gracilaria changii cultured in brackishwater ponds are an opportunity to develop multitrophic aquaculture between S. canaliculatus and G. changii. The study aimed to analyze the effect of salinity on the growth and food conversion of S. canaliculatus fed with G. changii. The study used a completely randomized design with three treatments and three replicates. The treatments included three different salinities, namely 35, 30, and 25 ppt. During the study, S. canaliculatus was fed fresh G. changii ad libitum, starting with 500 g. The availability of the feed in the tanks was checked every day and a 500 to 1,000 g of seaweed G. changii was added if its availability decreased. The remaining feed was weighed at the end of the study. The culture period was 60 days. The length and weight of the stocked Rabbitfish S. canaliculatus were 12.3±2.1 cm and 36.47±18.29 g. The stocking density was 10 Rabbitfish S. canaliculatus for each tank. The length and weight at the end of the study were 14.1±1.8 cm and 55.73±21.74 g. The increase in length and weight was 1.71±0.87 cm and 19.26±10.52 g. The absolute and relative length growth rates were 12.04 to 21.45 mm and 0.17 to 0.31 mm. The absolute and relative weight growth rates were 16.21 to 23.11 g and 0.23 to 0.32 g. The feed conversion was 62.26 to 75.95. The survival rate was 100% for all salinity treatments. The absolute and relative length growth of Rabbitfish S. canaliculatus was not significantly different between all salinity treatments. The total and relative weight growth of the rabbitfish S. canaliculatus was also not significantly different. The conversion of G. changii seaweed to Rabbitfish S. canaliculatus was not significantly different between all salinity treatments. The water quality parameters during the study supported the life of the Rabbitfish S. canaliculatus.