Cobia culture in Taiwan: current status and problems

Abstract

Cobia, Rachycentron canadum, is a widely distributed species from the Indo-Pacific waters to the southern Atlantic Ocean. In Taiwan, it is an indigenous and an ideal species for cage culture. Due to its high market value in both domestic and international markets, the technology for its culture has rapidly developed in the past few years. These include mass propagation through natural spawning of captive broodstocks, larval rearing techniques, nursery production in tanks, ponds and nearshore cages, and grow-out culture in offshore cages. Reproduction in captivity is relatively easy because sexual maturity often occurs within 2 years of culture. Spontaneous spawning occurs year around at water temperatures of 23–27 °C, with peak during spring and autumn. Fertilized eggs hatch within 21–37 h at water temperature of 31–22 °C. Larval growth is fast, and larvae are vitally robust and environment tolerant compared to other marine fishes. Fry can be mass-produced in outdoor ponds at relatively low cost. Weaning of fry from 20 days old onwards to pellet feeds is feasible. Nursery rearing from 10–30 to 1000 g can be done in either outdoor ponds or nearshore cages. Major diseases affecting cobia include bacterial (pasteurellosis, vibriosis and streptococcosis), parasitic (myxosporidea, Trichodina, Neobenedenia and Amyloodinium infestations), and viral (lymphocystis) ones. In recent years, intensive and super-intensive recirculation systems for nursery (from 2 to 100–150 g) were developed with survival rates of more than 90%. In nursery and grow-out offshore cages, 100–600 g cobia were cultured within 1–1.5 years when they reached 6–8 kg for export to Japan, or 8–10 kg for the domestic market. Currently, around 80% of marine cages in Taiwan are devoted to cobia culture. However, some problems still exist in cobia culture that needs to be addressed and solved to increase production. These include high mortality due to stress during transport from nursery tanks/inshore cages to grow-out cages and diseases during nursery and grow-out culture resulting in low survival, and consequently poor harvest.