Effects of feeding rate and sediment depth on the survival, growth performance, and biomass of mud polychaete Marphysa iloiloensis from early juvenile to adult in grow-out tanks

Polychaete aquaculture has progressed in some countries to meet the high demand of fish bait and aquaculture industries. However, knowledge on the aquaculture requirements of polychaetes in the grow-out is still scarce. The present study aimed to determine the optimal feeding rate (FR) and sediment depth (SD) for the grow-out culture of mud polychaete Marphysa iloiloensis from early juvenile to adult stage. The effects of two FRs (50 and 100 g m-2) with three different levels of SD (2, 3, and 5 cm) on M. iloiloensis survival, growth performance, and biomass were evaluated. The study was performed in a 2 x 3 factorial experiment using completely randomized design with four replicates per treatment that lasted 120 days. Early juveniles (30 days old) were stocked in glass tanks at 1000 individuals m- 2 and grown for 120 days (herein refer as 'adult', with musculature and capable of reproduction). Regardless of FR, M. iloiloensis had the highest survival of 45 +/- 2% in 5 cm SD but statistically comparable to 3 cm SD (34 +/- 5%), while survival was significantly lowest in 7 cm SD (26 +/- 3%). The levels of nitrite (NO2) and total ammonia nitrogen (TAN) was significantly higher in the rearing water of 100 g m- 2 FR than in 50 g m- 2 FR. Higher FR resulted to poor water quality and appeared to contribute to the low M. iloiloensis survival in 100 g m- 2 FR. Growth performance was similar among treatments. There was a significant interaction between FR and SD on M. iloiloensis biomass (p < 0.05). In 50 g m- 2 FR, no difference was observed in the different levels of SD while in 100 g m-2 FR, biomass was significantly higher in 5 cm SD than in 7 cm SD (p < 0.05). M. iloiloensis biomass in 50 g m-2 FR was higher compared to 100 g m- 2 FR, regardless of the SD. Overall, the culture of M. iloiloensis using 50 g m- 2 FR in 3-5 cm SD showed the best survival and biomass. Based on these findings, it is recommended that the grow-out culture of M. iloiloensis from early juvenile to adult should follow the 50 g m-2 FR and should be done in tanks with 3-5 cm SD to improve production.