Enhancing crab broodstock spawning and water quality using a recirculating aquaculture system with polychaete-assisted sand biofilter
2025
Calunod, Charles Van | Maceren-Pates, Mercedes | Pates, Gaudioso, Jr. | Nemeño, Derly | Quinitio, Emilia | Parado-Estepa, Fe D. | Arcilla, Mark | Añasco, Leny
The increasing global demand for mangrove crabs (genus Scylla) and threats to the wild populations highlight the urgency of fully rearing them in captivity. The supply of hatchery seedstock is still inadequate to meet the requirements for farming. One of the major causes is the inconsistent larval quality in the hatchery, which appears to be due to poor broodstock performance. The present study evaluated the efficiency of two broodstock holding systems: the Recirculating Aquaculture System (RAS) with a polychaete-assisted biofilter and the conventional system with regular water replacement, referred to as non-RAS (NRAS, control), based on the survival rate, spawning, and hatching of S. serrata captive broodstock. The percentage survival of mangrove crab broodstock was similar in the RAS (54.00±10.00) and NRAS (50.84±3.89) systems. However, a significantly higher mean percentage of spawning (28.61±6.65) and hatching (28.61±6.65) was observed in the RAS compared to the NRAS (15.18±7.41 and 15.18±7.41, respectively). Temperature levels were recorded in the RAS, ranging from 27.7-29.3°C, and that of NRAS was 26.7-28.5°C. Salinity in RAS ranged from 33.7-35.2 ppt, while in the NRAS, it ranged from 33.5-34.7 ppt. Dissolved oxygen (DO) concentrations ranged from 5.8 to 7.3 mg/L in RAS and 5.5 to 7.3 mg/L in NRAS. Additionally, pH values in the RAS ranged from 7.8 to 8.6, compared to 7.8-8.5 in the non-RAS. Moreover, ammonia levels were significantly lower in the RAS, 0.11-0.25 mg/L, compared to 0.31-1.18 mg/L in the NRAS. Similarly, nitrite concentrations were significantly lower in the RAS (0.001-0.007 mg/L) than in the NRAS (0.013-0.026 mg/L). This suggests that RAS with a polychaete-assisted biofilter enhances the reproductive performance of the mangrove crab S. serrata.
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