TOTAL REPLACEMENT OF DIETARY FISH OIL WITH A BLEND OF VEGETABLE OILS IN THE MARINE HERBIVOROUS TELEOST Siganus canaliculatus

The rabbitfish Siganus canaliculatus is a marine herbivorous teleost and feeds on algae and seagrass in nature. S. canaliculatus is a commercially valuable marine teleost fish widespread along the Indo-West Pacific coast and has become one of the most harvested species in southeastern Asia, including along the coast of southeast China. Therefore, the development of a suitable formulated diet is necessary for the culture industry. In our recent studies, we reported that S. canaliculatus may have the ability to convert 18:2n-6 and 18:3n-3 into long-chain polyunsaturated fatty acid (LC-PUFA) in both brackish water (10 ppt) and seawater (32 ppt), which suggested that fish oil (FO) may be partially or completely replaced by vegetable oils (VO). Moreover, our preliminary research results revealed that soybean oil (SO) can replace up to 67% or 45% of total dietary FO for S. canaliculatus without negatively compromising the growth performance or nutritional quality of fish.

To investigate the feasibility of total replacement of dietary FO with VO, and the optimal ratio of lipid sources and PUFA level in S. canaliculatus, six isonitrogenous (32% crude protein) and isolipidic (8% lipid) diets were formulated using different lipid sources. FO was used as the sole lipid source in the control diet (FOc), whereas varying blends of palm oil, SO, rapeseed oil, and linseed oil were used in diets VO1 - VO5, in which the dietary PUFA level was 41.95%, 38.18%, 33.83%, 29.94% and 27.12%, respectively. After S. canaliculatus juveniles were fed with the diets for 9 weeks, the growth performance exhibited no significant differences among all the dietary groups. The tissue fatty acids profile in liver and fillet generally reflected the dietary fatty acid composition, and showed no significant difference among the VO dietary groups. The results suggested that dietary FO can be totally replaced by VO in rabbitfish concerning the growth performance. Considering the resources and price of the experimental VO, diet VO2 with a blend of palm oil, SO, rapeseed oil, and linseed oil in a ratio of 2:2:1:1, and the dietary PUFA level was 38.18% of total fatty acids, was recommended.

Keywords: Siganus canaliculatus; dietary PUFA level; lipid selectivity; growth performance; fatty acid composition.

This work was financially supported by the Major International Joint Research Project from National Natural Science Foundation of China (NSFC) (31110103913) and NSFC General Projects (No. 41276179).