Stocking density is well known as an important field in aquaculture. Although many studies on stocking density have been conducted, however effects of rearing grouper (Epinephelus coioides) with different densities in recirculation and flow-through system are not well known. In this study, grouper juveniles (14.22 ± 0.67 g) were reared into 100-L aquaria at 15, 20 and 25 fish/aquaria and cultivated for 70 days. Statistical analyses showed that the highest growth performances observed in group reared at high densities (25 fish/aquaria) in recirculation system (R25), with an average final body weight and length were 95.82 ± 4.24 g and 18.72 ± 1.40 cm, respectively. Significant increase in weight gain and specific growth rate and decrease in food conversion ratio were observed in R25 after 10 weeks. However, no statistically significant different was found in survival rate and condition factor in all treatments. This study found that the effects of stocking density on growth and feeding ratio were higher in recirculation system compared with flow-through system. Further analysis determined that high stocking density in recirculation system and medium density in flow-through could affect the growth, feeding and fish behavior of this species.

The knowledge of the biological aspects and feeding activity of fish is required to manage the lack of data on fisheries. In this study, a total of 200 Plotosus canius were caught and examined to obtain information on their biological aspects, length-weight relationship, and feeding activity. The fish were captured using a gill net and traditional fishing trap called Bubu. Subsequently, all samples were examined for total body weight, total length, condition factor, gonad maturity, and feeding activity. The results showed that the specimens captured were 156 males and 44 females weighing between 95-280 gr and 117-214 gr with the length of 26-39 cm and 28-36.3 cm, respectively. The length-weight relationship showed a negative allometric growth pattern. The mean condition factors of males and females were 1.1048 and 1.0102, respectively. At the same time, the maturity level of gonads was at I and II. Moreover, it was discovered that most organisms in the digestive tract were shrimp, worms, small fish, and crabs, while the highest index of preponderance was in shrimp with 42%. In conclusion, this study showed the new information about length-weight, biological condition, and feeding habits of Plotosus canius, which can be inventoried to strengthen data on sustainable fisheries management.