Cobia culture in Taiwan: current status and problems

Aquaculture 237 (2004) 155 165 www.elsevier.com/locate/aqua-online Cobia culture in Taiwan: current status and problems I Chiu Liao a,b, *, Ting-Shih Huang c, Wann-Sheng Tsai c, Cheng-Ming Hsueh d, Su-Lean Chang e, Eduardo M. Leaño a a National Taiwan Ocean University, Keelung 202, Taiwan b National Pingtung University of Science and Technology, Pingtung 912, Taiwan c Penghu Marine Biology Research Center, Fisheries Research Institute, Paisha, Penghu 884, Taiwan d No. 32, Nei-an Village, Siyu Township, Penghu, Taiwan e Tungkang Marine Laboratory, Fisheries Research Institute, Pingtung 928, Taiwan Received 18 November 2003; received in revised form 27 February 2004; accepted 2 March 2004 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 jc, with peak during spring and autumn. Fertilized eggs hatch within 21 37 h at water temperature of 31 22 jc. 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 * Corresponding author. Department of Aquaculture, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan. Tel.: +886-2-24623055; fax: +886-2-24634994. E-mail address: ichiu619@yahoo.com (I C. Liao). 0044-8486/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2004.03.007

156 I C. Liao et al. / Aquaculture 237 (2004) 155 165 transport from nursery tanks/inshore cages to grow-out cages and diseases during nursery and growout culture resulting in low survival, and consequently poor harvest. D 2004 Elsevier B.V. All rights reserved. Keywords: Cobia culture; Broodstock management; Larval rearing; Nursery; Grow-out; Disease problems 1. Introduction Cobia, Rachycentron canadum, is widely distributed in tropical and sub-tropical waters (Briggs, 1960; Hassler and Rainville, 1975; Chen, 1986; Ditty and Shaw, 1992), and it has been cultured as a recreational fish species. However, because of its good meat quality (Shiau, 1999; Chen, 2001), its potential for aquaculture was recognized in recent years. In Taiwan, cobia is now popularly cultured in sea cages either for domestic consumption or for export, mainly to Japan (Su et al., 2000; Her et al., 2001; Liao, 2003). Its culture began in the early 1990s when the technology of mass fry production was developed in 1997 (Chang et al., 1999). To date, several marine fish hatcheries are producing cobia fingerlings for stocking in nursery tanks or inshore cages. The different phases of cobia production in Taiwan are shown in Fig. 1. Marine cage aquaculture is getting popular in Taiwan where land and freshwater resources are limited (Su and Liao, 2001). Among many species of cultured marine fish, cobia is a prominently popular species for cage aquaculture because of its fast growth rate and comparatively low production cost. Total cobia production increased from 1800 mt in 1999 to 3000 mt in 2001, but plunged to 1000 mt in 2002 due to high incidence of disease outbreaks and losses from typhoon damage (Fig. 2). The domestic consumer acceptability, however, increased resulting in the higher market price. Fig. 1. Flowchart of cobia aquaculture in Taiwan.

I C. Liao et al. / Aquaculture 237 (2004) 155 165 157 Fig. 2. Annual production of cobia in Taiwan. *Low production is due to high incidence of disease outbreaks and loss due to typhoons. With increasing interest in cobia production, culture system in both nursery and growout cages was intensified. This paper presents review and current status of cobia culture in Taiwan including broodstock management, mass fry production and nursing. It also describes development of intensive and super-intensive recirculation system for fry nursing, current production in grow-out cages, marketing, as well as problems encountered in the whole production process. 2. Broodstock management and mass fry production The purpose of broodstock management is to supply good quality eggs and larvae, which generally include collection, selection, and domestication of broodstock, appropriate feeds, maturation and spawning, and egg collection and incubation (Liao et al., 2001). In the case of cobia, broodstocks were usually collected from the wild before artificial propagation was developed. Currently, cobia intended for broodstock are produced from hatcheries and reared in open cages until they attain sexual maturity (about 1.5 2 years when fish weighs about 10 kg). Handling and spawning of mature brooders have been described in detail (Su et al., 2000; Liao et al., 2001; Liao, 2003). Maturing brooders are selected from sea cages and transferred to land-based spawning ponds (400 600 m 2 area; 1.5 m depth) with flow-through seawater, at a density of 100 fish per pond and a sex ratio of about 1:1 (male/female). Fish are fed to satiation with raw fish (e.g. sardines, mackerels, squids) once or twice a day. Brooders spawn spontaneously year around, with a peak in spring and autumn when water temperature is maintained at 23 27 jc. The fertilized eggs are collected using a seine net installed against the current created by paddlewheels. The eggs are then transferred to outdoor larval rearing ponds (earthen ponds; < 5000 m 2 area ; 1 1.2 m water depth) with well-maintained green water (Chlorella sp.) and abundant number of copepods. Water exchange is minimal or unnecessary in the early stage as long as the green water is maintained.

158 I C. Liao et al. / Aquaculture 237 (2004) 155 165 Eggs hatch 21 37 h after fertilization at temperature of 31 22 jc. Cobia larvae are vigorous and more resistant to some stressors compared to other tropical marine fish (e.g. grouper). They open their mouth and starts feeding at day 3 after hatching. Rotifers and copepod nauplii are provided at this stage, with higher preference to copepods during the first feeding stage. Larvae are reared up to day 20 with survival rate of 5 10%. 3. Fry nursery The cobia fry are nursed in three phases (Fig. 1). The first phase includes rearing the fry from 0.2 to 2 5 g (day 20 to day 45). At this stage, the fry grow rapidly into fingerlings, reaching 8 10 cm at the end of the first nursery phase. Size grading is undertaken once every 4 day to 1 week. At this stage, the fry can be totally weaned to floating pellet feeds. In the second nursery phase, cobia fingerlings are reared from 2 5 to 30 g (day 45 to day 75) in large ponds (>300 m 2 ) with green water. Feeds are provided manually to satiation five to six times daily at the weaning stage. The size of the pellet feeds is increased gradually as the fish grows. Feeding rate on the other hand is reduced from 5% body weight (BW) for 10 30 g to 2 3% BW for 100 200 g. Size grading is undertaken only once during this stage. In the third nursery phase (from 30 to 600 1000 g; day 75 to day 150 180), the cobia are cultured either in outdoor ponds or inshore cages. Size grading is usually done only once during this stage. It is not advisable to stock cobia juveniles smaller than 30 g in offshore cages because of their weak resistance to strong water current, also the necessity in occasional grading to prevent cannibalism, and prevention of mortality due to bacterial infections. Moreover, the smaller mesh size needed for small-sized cobia prevents water current flow inside the cage, resulting in higher incidence of parasitic infestation. Some family-owned and commercial cage farms are located in protected bays, such as in Shao-Liu-Chiu island in Southern Taiwan, where the second and third nursery phases are carried out in the same area as the grow-out cages to avoid mortality associated with transportation stress. Small cobia (2 5 g) are more tolerant to transport stress than the larger ones (Liao, 2003). Recently, a recirculation system was designed for nursing cobia fry (4 8 g) under intensive and super-intensive rearing and mass production of juveniles (100 150 g) for stocking in offshore grow-out cages (Huang et al., 2002). Several trial runs confirmed efficiency of the system for rearing of cobia fry at high stocking density. Table 1 shows the result of one trial run using the intensive recirculation system at different stocking densities (125, 250, 370 and 500 fish/m 3 ). Survival rate at all stocking densities tested was above 95%. Results show that optimum stocking density using this system is 370/m 3 based on survival, specific growth, and food conversion rates. In 2001, this system was employed to produce 34,000 fish of 150 g cobias, which were supplied for offshore growout cage culture. A super-intensive recirculation system was also designed to culture cobia fry at higher densities than the intensive recirculation system, especially during over-winter stage. The recirculation system was equipped with temperature control apparatus, microstrainer, drumfilter, protein skimmer, biological filter, automatic water supply and drain system,

I C. Liao et al. / Aquaculture 237 (2004) 155 165 159 Table 1 Growth performance of cobia in intensive recirculation nursery system at different stocking densities after 4 weeks of culture Stocking density (fish/m 3 ) 125 250 370 500 Initial weight (g) 7.1 F 0.2 7.5 F 0.7 7.3 F 0.4 7.2 F 0.2 Final weight (g) 92.1 F 1.3 a 85.2 F 4.0 b 75.9 F 3.8 c 69.7 F 2.2 d Specific growth rate (SGR; %) 8.6 F 0.1 a 8.1 F 0.4 a 7.8 F 0.1 ab 7.6 F 0.1 b Feed conversion rate (FCR) 0.96 F 0.02 b 0.94 F 0.01 b 0.99 F 0.01 a 1.00 F 0.02 a Survival rate (%) 97.8 F 1.9 a 97.8 F 0.9 a 96.0 F 1.2 a 95.2 F 1.6 a Production (kg/m 3 ) 11.3 F 0.2 d 20.7 F 1.1 c 28.3 F 2.1 b 33.5 F 0.7 a Values are mean of three replicates. Row means ( F S.E.) with the same letter superscript are not significantly different ( P>0.05). oxygenation unit, and UV sterilizers (Huang et al., 2002). Using this system, step-wise trial runs were conducted with three stages of culture at stocking density as high as 594 fish/m 3. The first stage was from 4 g (initial weight) to 18 g during the first 15 days of culture. The second stage was 45-day culture when cobia reached 45 50 g, and the third stage was 30-day culture with final weights of 100 g or larger. Survival rate ranged from 92% to 100% in the three stages. In 2002, this system produced more than 80,000 cobia with body weights of 120 320 g which were then transported to offshore cages for grow-out. 4. Grow-out Cobia are cultured in offshore grow-out cages for the final production stage until they reach the market size of 6 8 kg (for export) or 8 10 kg (for domestic consumption). Culture period ranges between 6 and 8 months depending on the market size. In Taiwan, there are two types of offshore grow-out cages for cobia production: small family-owned cage farm; and big commercial cage farm. As mentioned earlier, most of these cage farms integrate nursery and grow-out culture in one area, for convenient transfer of fish stocks from the nursery to grow-out cages. A typical family-owned cage farm is shown in Fig. 3, where rectangular cages are used in the first and second nursery phases. Circular cages are used for grow-out, which measures 8 12.7 m in diameter and 7 8 m depth corresponding to a total water volume of 350 1000 m 3. The stocking density and expected harvest at the nursery and grow-out stages are summarized in Fig. 3. For commercial cage farms, bigger circular cages are used for the nursery phase (Fig. 4). Each nursery cage is 7 m in diameter and 5 m in depth, where 30 g cobia are stocked and cultured for 4 5 months when cobia are about 800 g and ready for transfer in growout cages. Each grow-out cage measures 16 m in diameter and 9 m in depth. In one commercial cage farm, highest average production was 25 mt per 1800-m 3 cage after 6 8 months of culture (personal communication). Sinking and floating pellet feeds are used for cobia in grow-out cages. The pelleted feeds has a crude protein (CP) content of 42 45% depending on feed manufacturers.

160 I C. Liao et al. / Aquaculture 237 (2004) 155 165 Fig. 3. Culture operation of a typical family-owned cobia cage farm in Taiwan.

I C. Liao et al. / Aquaculture 237 (2004) 155 165 161 Fig. 4. Culture operation of a typical commercial cage farm for cobia in Taiwan.

162 I C. Liao et al. / Aquaculture 237 (2004) 155 165 Usually, feeds manufactured exclusively for cobia culture have higher CP as well as fish oil contents (15 16%), which are more expensive than feeds produced for other marine fish. Fish are usually fed once a day and 6 days a week, depending on the weather condition, at a feeding rate of 0.5 0.7% BW. The feed conversion ratio in grow-out stage is about 1.5. Survival rate at harvest for family-owned cage farms ranged from 50% to 70% while that of commercial cage farms is only 30% to 40%. 5. Harvesting and marketing After 4 8 months of grow-out period, fish over 6 kg are selectively harvested for local market or exporting to Japan. The stock is usually starved for one day prior to harvest. Right after harvest, fish are killed, bled and chilled prior to transporting to processing plants, where fish are thoroughly rinsed and packed in layers of ice in insulated boxes. Fish are sold whole for the domestic market, while those exported to Japan for the sashimi market are sold either whole or headless. For markets other than Taiwan and Japan, cobia is processed as fillet. In 2002, total cobia production in Taiwan was recorded at only 1000 mt due to high incidence of disease outbreaks and losses due to typhoons. Most of the harvested produce were only sold in the domestic market. Currently, the domestic price for cobia larger than 8 kg is 180NT$/kg (1US$ = 33NT$), 170NT$/kg for 7 8 kg, 160NT$/kg for 6 7 kg, and 150NT$/kg for < 6 kg. 6. Problems 6.1. Diseases The initial success of cobia production in the late 1990s has resulted in increase in number of cage farmers, as well as intensification of the culture system to increase production. As such, several disease incidents occurred in recent years causing dramatic reduction in production during 2002. Diseases caused by bacteria, virus and parasites occur in all stages of culture of cobia. During the larval stage, problems encountered include Epistylis and Nitzchia infestations. During the nursery stage, a viral disease (lymphocystis) is common but not fatal, as long as good water and feeding management are employed. The parasite Amyloodinium ocellatum also cause problems, which can result in high mortality when left uncontrolled. Trichodina infestation is also common during the nursery stage. Myxosporidean infestation was also reported among cobia juveniles (45 80 g) reared in nursery cages causing mass mortality (about 90% within 1 month) (Chen et al., 2001). In the grow-out stage, the ectoparasite Neobenedenia sp. is common which, together with secondary bacterial infection (by Streptococcus sp.), can cause blindness of cobia juveniles. The feeding activity of blind cobia is highly affected resulting to slower growth, dark body coloration and lower market value. Pasteurellosis, caused by the bacterium Photobacterium damsela subsp. piscicida, is one of the major problems among cage-cultured cobia juveniles (Tung et al., 2000), especially during the onset of the winter season. Mass mortality is usually experienced

when outbreaks of pasteurellosis occur. Another bacterial disease problem in grow-out sea cage culture is vibriosis. The first vibriosis outbreak was recorded in 2000 (Rajan et al., 2001) which caused 45% loss in stocks. The disease caused by Vibrio alginolyticus has characteristics of hemorrhagic lesions on skin and skeletal muscles. Other secondary invaders include V. vulnificus and V. parahaemolyticus. 6.2. Environmental condition Taiwan is a sub-tropical country situated in the western Pacific rim where strong typhoons occur annually, during summer and autumn seasons. Low water temperature is also encountered during the winter season in the central and northern parts of the country. Since one culture production run of cobia requires at least 1 year (12 months), the risk of losing stocks in offshore cages during typhoon season is high. As such, some cage farmers, especially family-owned farms, install culture cages in protected bays and coves, where water current is weak. Most of these areas, however, also harbors fishing boats, thus oil spills are common. Cobia cultured in these protected areas have lower meat quality (inferior in terms of chewiness) compared to those cultured in open sea areas exposed to strong current. Moreover, meat often tastes oily. Over-wintering is another problem for grow-out cages in central Taiwan, especially in Penghu islands, where water temperature may drop to a low of 16 jc during the winter season. Growth of cobia is usually retarded at low temperature and sometimes, high mortality also occurs when temperature decreases to below 16 jc. As a result, culture period in these sea-cage areas is longer (up to 17 months) compared to sea-cage areas in southern Taiwan (11 14 months) where the water temperature range is 23.5 28 jc all year round. 6.3. Others I C. Liao et al. / Aquaculture 237 (2004) 155 165 163 Cobia is not very resistant to stressors and requires high level of dissolved oxygen because of their high metabolic rates due to their active behavior. As such, mortality problem during transport is still considered as one of the most serious problems in cobia culture. Improvement in the transportation of cobia, especially juveniles, was recommended since the development of cobia culture in Taiwan (Liao, 2003), but no such improvement has yet been devised. Marine cage culture is popular in Taiwan but regulations for open ocean aquaculture are still lacking (Su and Liao, 2001). As cobia cannot survive below 16 jc, most of the sea cages are located in Southern Taiwan where tropical climate prevails. These areas, however, are also utilized for fishing and other purposes (Liao, 2003), thus competition for available sea area is apparent. The government plays an important role in the overall development of the cobia culture industry. However, the current policy on aquaculture is somehow inappropriate for cobia cage culture industry. Aside from the disease outbreaks and some environmental problems, the lack of good planning and regulatory enforcement when cobia was developed as a potential aquaculture species has led to non-sustainable production in the past few years. Some policies even hinder further development of cobia culture in offshore cages. Thus, Taiwan lose international competitive advantage for the

164 I C. Liao et al. / Aquaculture 237 (2004) 155 165 export industry among many Asian countries which are venturing in cage culture of cobia. With the high risk associated with off-shore cage aquaculture, the lack of insurance policy from the government is also of serious concern for most cage farmers. 7. Prospects and future development Although many disease and environmental problems are faced by aquafarmers in Taiwan, cobia remains to be the most popular species for culture in offshore cages. This is because of its fast growth, high market value, good meat quality, the established technology in mass production of larvae, the current innovation in intensive and superintensive nursery rearing in tanks, and improved formulated feeds. However, the lack of regulations in open ocean aquaculture in Taiwan has resulted in the uncontrolled proliferation of sea cage farms. Nonetheless, this interest of fish farmers to venture into cobia production, and the continuously increasing production since its introduction in the 1990s, only proves the profitability of cobia cage culture compared to other marine fishes. Disease outbreaks remain to be the biggest threat in cobia culture in Taiwan, causing a significant decline in total production in 2002. At present, researches on the development of vaccines against major bacterial pathogens (P. damsela subsp. piscicida, V. alginolyticus, and Streptococcus sp.) are undergoing. Another alternative approach to this problem is the use of immunostimulants (e.g. h-glucan, levamisole, etc.) to enhance the nonspecific immunity of fish to various diseases. Stocking of more resistant large-sized fish in offshore cages also contributed in preventing apparent loss of stocks due to diseases. Disease surveillance must also be strengthened and continuously undertaken to monitor disease outbreaks. Moreover, selective breeding must also be urgently employed for improving both growth and resistance to diseases. With the recent developments in both nursery and grow-out culture of cobia, improvement in many aspects of production is still needed. Automation in terms of feeding, grading, thinning, harvesting, and net washing are still needed to be developed as these activities are highly labor intensive especially in offshore grow-out cages. The recent innovation of the intensive and super-intensive recirculating system for nursery rearing can only be applied in rearing cobia juveniles for up to 300 g. This system allows the transfer of cobia juveniles directly into offshore nursery cages in the same area where the grow-out cages are located. This strategy prevents the occurrence of high mortality due to transportation stress of large-sized cobia. However, this system might be too expensive for many fish farmers as high investment is necessary to set-up the facilities. Therefore, other strategies in mass-production of cobia juveniles during the nursery stage should still be developed. One of which is the possibility of culturing cobia in ponds under semiintensive or intensive system. If this is successful, however, transportation problem will still be the issue to be resolved. Marketing of cobia produce should not only target domestic market but more importantly the export market. To have a sustainable export market, however, a floorproduction volume should be identified and maintained in order to supply the import demand of foreign countries. This is important in order to maintain the competitiveness of the cobia export industry in Taiwan.

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