Simple techniques double crablet production
Crab farmers will be happier, and the environment hopefully better, with recent improvements at the mangrove crab hatchery of the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC/AQD) in Iloilo, Philippines.
Crablets used in the farming of the prized mangrove crabs, Scylla serrata, are usually collected from the wild and increasing demand has threatened their natural population with crablets becoming more difficult to find.
“Overfishing has pushed the local government of areas heavily exploited for crablets such as Catanduanes, Surigao, and Samar. They have implemented strict prohibitions in the collection of wild crablets,” said Joana Joy Huervana, associate researcher at SEAFDEC/AQD and leader of the mangrove crab team.
Restrictions on wild collections in the Philippines led to the rise in demand for hatchery-bred crablets. Unfortunately, crab hatcheries suffer from very low survival rates caused by disease and cannibalism.
However, Huervana recently revealed that simple tweaks in protocols at the SEAFDEC/AQD hatchery have led to a significant boost in their crablet production, with survival increasing twofold.
By feeding the crabs more frequently and providing cleaner water in the tanks, Huervana reported that they were able to increase the average survival rate from zoea (newly-hatched larvae) stage to crablet, from an average of one percent in 2017 to two percent in 2019.
Two percent might seem low to those unfamiliar with the hatchery business, but Huervana says crabs produce an average of 3 million larvae which translates to 60,000 crablets per spawner. She further disclosed that SEAFDEC sells crablets, as a byproduct of research, at US$ 0.10 per piece but wild crablets sold by traders in the Philippines reach as much as US$0.24 to US$0.30 per piece.
The simple tweaks helped them achieve the higher survival rate from zoea to crablet, reaching as much as 10 percent sometime last year, which contributed to the hatchery’s production of over 650,000 pieces of crablets for 2019.
Increased feeding frequency, cleaner water
“Feeding frequency was increased from four to six times a day with an interval of four hours,” Huervana shared, which is “based on the crabs’ biomass at 100 percent feeding rate.”
She said the intervention worked because cannibalism among the crabs is more prominent starting in the megalopa stage (intermediate larval phase), therefore increasing the available feeds, together with providing additional shelters in the larval tanks, increased the survival.
“As for the water replacement, the interval was shortened from five to four days. Siphoning of tank bottom to remove dead larvae, microalgae, and feeds is done every three days to further improve water quality. Also, monitoring of water parameters was consistently conducted,” Huervana added.
“These techniques were tested throughout the years and were proven effective. It could also be easily adapted by hatchery owners and other stakeholders,” Huervana shared.She added that further improvements are still being done in the SEAFDEC/AQD hatchery, not only to cope with the industry’s demand for crablets, but also to improve the science behind the technology of mangrove crab hatchery.
“We do our share in alleviating the pressure caused by overfishing in the wild by continuously improving production techniques of our mangrove crab hatchery to share with our stakeholders.”
Press release courtesy of SEAFDEC AQD.