By Dr. Rafael D. Guerrero III
The National Integrated Fisheries Technology Center (NIFTC) of the Bureau of Fisheries and Aquatic Resources (BFAR) in Barangay Bonuan Binloc, Dagupan City in Pangasinan is one of the leading research and development centers for aquaculture in the country, and is headed by Dr. Westly Rosario. The center is credited for the hatchery development of many cultured species such as milkfish, freshwater prawn, saline tilapia, sea cucumber, and siganids with funding support from the government and international institutions.
Siganids, locally known as “malaga” or “samaral,” are marine fishes that are also called “rabbitfishes” because their snouts look like those of rabbits. Although naturally occurring in the wild where they inhabit mangroves, sea grass beds, and reef flats, there has been a decline in the fishery catch of these fish because of overfishing and habitat degradation. Of the 26 species of siganids in the country, the two most commonly cultured in brackish water ponds and pens, and sea cages are the Siganus guttatus (spotted) and Siganus vermiculatus (striped).
Siganids are herbivores (feeding on plants like filamentous algae) and omnivores (feeding on supplemental feeds and formulated diets). They are valued over milkfish and tilapia in local markets and have good export potential. Despite these desirable qualities, however, siganids only contribute less than one percent of our total farmed fish production. The main limitation for their mass production is the lack of reliable sources of fry for culture. Supply of wild fry is highly seasonal—only from March to July—and only available in certain areas.
Through the years, researchers of the BFAR, Southeast Asian Fisheries Development Center’s Aquaculture Department, Mindanao State University-Naawan, and Silliman University have contributed to the knowledge and technologies for the hatchery and culture of siganids in the country. There are now two government-run hatcheries—the NIFTC’s and that of MSU-Naawan in Misamis Oriental—and a private hatchery in Sarangani Province (Finfish Hacheries, Inc.), that commercially produce siganid fry.
At the NIFTC’s siganid hatchery, pond-reared breeders of S. guttatus and S. vermiculatus weighing 200-250 grams each are first conditioned for spawning in concrete tanks with filtered seawater and aeration, and fed a high-protein diet. The female breeders are larger than the males that mature in less than a year. In a 2 x 2 x 1 meter tank with a water depth of 0.5 meters, a fine-mesh net enclosure (hapa) is placed with two males and a female. Spawning occurs at night during the first quarter of the lunar cycle every month for the S. guttatus and during the last quarter phase of the moon for S. vermiculatus throughout the year for both species.
A female breeder produces 300,000-400,000 eggs per month that are fertilized by milt from the males in the net enclosure. The fertilized eggs hatch after 18-35 hours at water temperatures of 22-30OC. The floating larval fry (with yolk sac) are then collected from the enclosure and stocked in the tank before the breeders are removed with the enclosure.
After 3-5 hours, the yolk sac of the larvae is absorbed and the fry start to feed on their own. Cultured natural food (rotifer) is given to the fry during the rearing period of 45 days, after which the fry weighing about a gram each—can be sold to fish farmers at P1/piece. While the survival rate of the fry after the rearing period ranges from 4.3 to 38% in experiments, the survival rate at the NIFTC hatchery is only 3%.
The NIFTC achieved a major breakthrough in 2010 with the production of S. guttatus and S. vermiculatus hybrids through natural spawning in tanks. While S. guttatus is preferred by consumers for its better taste, it does not grow as fast as the S. vermiculatus. It is believed that the hybrids have the desirable characteristics of their parents. Interestingly, the hybrid spawns during the new moon phase of the lunar cycle.
This appeared in Agriculture Monthly’s January 2018 issue.