The study was carried out to evaluate the use of green weed (Cladophora sp.) as a partial substitute commercial feed in Tilapia (Oreochromis sp.) culture in the brackish water pond at Bac Lieu province, Vietnam. The trial comprised four feeding treatments that were randomly assigned in triplicate. (1) Fish were fed a single commercial feed (CF) every day as a control; in the other three treatments, fish were fed green seaweed Cladophora (CL) every day, of which (2) was a single CL; (3) and (4) were a combination of CF and CL, with CF being given every two days and every three days, respectively.

After 90 days of culture, feeding treatments had no effect (p>0.05) on tilapia survival, ranging from 96.67% to 98.89%. Fish performance in terms of final weight (144.58-206.35 g), specific growth rate (2.62-3.01%/day) and production (1.88-2.61 kg/m²) of which fish fed CL daily combined with CF every 2 days were comparable to the control group (p>0.05), with a lower feed conversion ratio and the cost of commercial feed could be reduced by 41.66%. Fish fillet analysis showed that fish fed commercial feed had the highest crude lipid content, while crude protein content was unaffected by green seaweed replacement in the feeding regime. These findings suggested that green seaweed Cladophhora sp. can be used as a feed to partially decrease commercial feed in the grow-out of tilapia.