Dietary seaweed (Ulva sp.) does not alter fatty acid profiles and concentration in South African juvenile dusky kob (Argyrosomus japonicus, Sciaenidae) fillet

Abstract

Seaweeds are potential feed additives for aquaculture but their effect on fish fatty acid content and profile is largely unknown. This study was, therefore, designed to assess the effect of incorporating green macroalgae seaweed (Ulva sp.) into diets of juvenile dusky kob (Argyrosomus japonicus) on fillet fatty acid profile and concentration. Five experimental diets were formulated to contain seaweed at the following inclusion levels: 0 (Ulva0), 50 (Ulva50), 100 (Ulva100), 150 (Ulva150) and 200 (Ulva200) g/kg commercial kob feed on a dry matter basis. Seventy-seven fingerlings (9.14 ± 0.30 g) were distributed into each of 20 experimental tanks and diets were randomly allocated to tanks such that each diet had 4 replicate tanks holding 77 fingerlings. There was no dietary effect on fillet fatty acids (FA) concentrations (P > .05). The concentration of C18:3n3 (α-linolenic acid) tended to increase with Ulva inclusion levels (P > .05). However, the opposite was observed with the fillet concentrations of both C20:4n6 (arachidonic acid methyl ester) and C20:5n3 (eicosapentaenoic acid (EPA)), but the decrease was also not significant. In conclusion, while Ulva-containing diets did not enhance the FA concentration in dusky kob fillet, the values were similar to those observed in fish fed on the relatively expensive commercial kob diet.

Keywords

• ulva sp
• fatty acid concentration
• argyrosomus japonicus
• south african aquaculture