64 JUNE 2018 • WORLD AQUACULTURE • WWW.WAS.ORG hatchery conditions. Wildsourced fish were shifted to the broodstock section when they were completely acclimated to hatchery conditions. Mortality occurred when fish were reared in the flowthrough system because of a protozoan infection (Samraj et al. 2011). Broodfish were then reared in recirculating aquaculture system and subjected to strict quarantine conditions to evaluate ecto- and endo-parasites and other suspected diseases. Fish were anesthetized with tricaine methanesulfonate (MS-222) to facilitate tagging and shifting to RAS from the quarantine tanks. Gonadal biopsy with a 1-mm diameter catheter was used to differentiate sexes. Broodstock diet. Quality seed production depends on good broodfish diet quality. An ideal broodstock diet is a pre-requisite to obtain greater fecundity, gamete quality and hatchling survival rate (Watanabe 1985, Bromage 1995). Good nutrition is essential to ensure egg yolk quality and endogenous nutrition for growing larvae (Rainuzzo et al. 1997). Protein and omega-3 fatty acid deficiencies in feed results in poor gamete viability and larval survival. An inappropriate dietary ratio of polyunsaturated fatty acids (PUFA) alters the circulating level of androgens, resulting in asynchrony of maturation between the sexes (Cerda et al. 1997). Vitamin C was added to the diet improved sperm concentration, motility, and fertility (Mangor-Jensen and Holm 1994) while PUFA boosts egg and larval development (Ma et al. 2005). Because there was no information available about standard cobia broodfish diets, fish were fed sardines and squid on an alternative basis in two rations, corresponding to 3-5 percent of fish body weight daily. Induced Spawning Captive breeding. Male cobia become sexually mature at 53 cm total length whereas female cobia mature at 68 cm total length. Cobia has a protracted reproductive season in Indian seas and Cobia Rachycentron canadum, also known as black kingfish, is the only species in the family Rachycentridae. It is commonly found throughout the world, except the central and eastern Pacific (Shaffer and Nakamura 1989). Cobia is a pelagic species found in the water column of the open ocean from the surface to a depth of 1200 m (Shaffer and Nakamura 1989). In recent years, cobia has become popular as a potential candidate species for aquaculture, related to its excellent growth performance and high market demand. Several successful attempts have been made to breed cobia. In India, the first successful breeding of cobia was achieved in 2010 at the Mandapam Regional Centre of Central Marine Fisheries Research Institute, Tamil Nadu (Gopakumar et al. 2010, 2012), followed by the Rajiv Gandhi Centre for Aquaculture at Pozhiyoor, Kerala (Samraj et al. 2011). Presently, seed production of cobia is being carried out on a commercial scale by both organizations. Broodstock Source and Management Broodstock transportation and hatchery acclimation. Broodfish were caught in the open ocean by angling and transported in 500- to 1000-L tanks at 50 kg/m3 to the hatchery. From these wild-caught fish, appropriate age and size fishes were selected as broodstock (Fig. 1). During handling, dissolved oxygen concentration in the broodstock tank was maintained at 8-12 mg/L with compressed oxygen cylinders. Water temperature was maintained at 22-26 C with ice packs. Clove oil (10-40 ppm) was used as an anaesthetic, facilitating ease of handling during transportation (Benetti et al. 2007, 2008). After reaching the hatchery, broodfish were treated with fresh seawater for two minutes and given a one-minute dip treatment with 100 ppm formalin to remove external parasites and treat lesions, then set aside in quarantine tanks for about 2-3 weeks for acclimation to Advances in Cobia Seed Production and Hatchery Management in India Kalidoss Radhakrishnan, Shajahan Ferosekhan, Samraj Aanand, A. Karthy and Aparajita Priyadarshani FIGURE 1. Cobia broodstock in a confined system. Photo: Fish Identification blogspot. FIGURE 2. A cobia broodfish being held for cannulation. Photo: NOAA photo library.
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