Developments in striped catfish hatchery technology (chapter 16)

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The parties submit to the non-exclusive jurisdiction of the English courts. Woodhead Publishing Online - T&Cs January 2011 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 16 Developments in hatchery technology for striped catfish (Pangasianodon hypophthalmus) P. T. Nguyen, T. M. Bui and T. A. Nguyen, Can Tho University, Vietnam and S. De Silva, Network of Aquaculture Centres in Asia and Pacific (NACA), Thailand and Deakin University, Australia DOI: 10.1533/9780857097460.3.498 Abstract: Striped catfish (Pangasianodon hypophthalmus) farming in the Mekong Delta, Vietnam, is considered as a major, aquaculture development both in Vietnam and globally. One of the main drivers responsible for the explosive growth of the sector is considered to be the development and commercialisation of techniques for artificial propagation of the species. This chapter looks first at the life-cycle of the striped catfish and historical developments in hatchery technology before going on to discuss induced breeding of catfish in hatcheries together with larval and fry nursing. Finally, harvesting and transportation are described and possible future directions in the sector. Key words: striped catfish, hatchery, fingerling, fry, spawning. 16.1 Introduction The Mekong Delta in the Southern part of Vietnam (8°33′–10°55′N; 104°30′–106°50′E) is renowned for catfish farming. There are two genera of catfish in Vietnam; the genus Pangasius comprising 10 species and two species of the genus Pangasianodon. Of these, the striped catfish (Pangasianodon hypophthalmus) (Fig. 16.1) is the most important and has been farmed for decades. For several decades, this species was farmed in small ponds using wild-caught seed (Nguyen, 2009); larger-scale commercial culture followed in cages, pens and ponds commencing with the development of artificial mass seed production in the early part of the last decade (Tuan et al. 2003; Phan et al., 2009; Bui et al., 2011). The total production of the striped catfish reached 1.2 million tonnes in 2011 (Fig. 16.2) (Fisheries © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 499 Fig. 16.1 Striped catfish Pangasianodon hypophthalmus (Sauvage, 1878). 1 200 000 1 050 000 Production (tons) 900 000 750 000 600 000 450 000 300 000 150 000 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 1 350 000 Fig. 16.2 Growth of striped catfish production in Vietnam, 1997–2011. Directorate, 2011). This fish species is now known worldwide due to its products being exported to 136 countries and territories in 2010 (De Silva and Phuong, 2011). The striped catfish has become the ‘Princess in Vietnamese aquaculture’ in recent years (Phuong and Oanh, 2010). One of the key drivers for the fast growth of the striped catfish farming sector is the successes of seed production and associated development of hatchery techniques, including the uptake and successful adoption of the techniques by the farming community. 16.1.1 Life-cycle of the striped catfish The striped catfish (P. hypophthalmus) is a migratory riverine species that undertakes long-distance migrations of more than several hundred kilometres between its upstream refuges and spawning habitats and its downstream feeding and nursery habitats (Van Zalinge et al., 2002; Baran, 2006). The life-cycle of the striped catfish is intimately tied to the annual monsoon © Woodhead Publishing Limited, 2013 500 Advances in aquaculture hatchery technology 16.1.2 Demand for striped catfish seeds The success of the artificial seed production is considered to be one of the key drivers for the explosive growth of the striped catfish in Vietnam (Phuong and Oanh, 2009). The production of hatchery-reared seed has increased rapidly during the past years; larvae and fingerling production increased 18-fold and 26-fold, respectively, between 2002 and 2011 (Fig. 16.3). The seed demand is mostly for fingerling size for grow-out stocking. 16.1.3 Historical developments in striped catfish hatchery technology Initially, the seed stock for striped catfish farming was wild-caught, primarily from Cambodian waters at the confluence of the Mekong, Bassac and Tonle Sap Rivers, the main nursery grounds of this species (Nguyen, 2009). However, the Cambodian authorities banned the capture of wild stocks in 16 000 14 000 Production (million) 12 000 10 000 8000 Larvae Fingerling 6000 4000 2011 2010 2009 2008 2007 2006 2005 2004 2003 2001 0 2002 2000 2000 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 flood cycle, with spawning in May–June at the start of the monsoon season (FAO, 2010–2012). The spawning ground of the striped catfish is generally known to be upstream of the Mekong River Delta, more specifically, below the Khone Falls on the Laos–Cambodia border (Van Zalinge et al., 2002). The fish spawns at the beginning of the rainy season and the adhesive eggs are deposited on roots of aquatic macrophytes and other substrates. The newly hatched larvae drift downstream and are swept into floodplain areas in southern part of Cambodia and the Mekong Delta of Vietnam. The striped catfish is a facultative air-breather (Lefevre et al., 2011) the airbreathing organ of this fish consisting of tiny blood vessels located around the palate which allow the fish to withstand low levels of dissolved oxygen. Fig. 16.3 Growth of striped catfish larvae and fingerlings in Vietnam (compiled by Phuong, 2011). © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Developments in hatchery technology for striped catfish 501 1994 (Ngor, 1999; Nguyen, 2009; Phuong and Oanh, 2010) and this ban led to a hiatus in the expansion of striped catfish farming. However, it also led to a concerted effort to study and develop artificial propagation techniques. Artificial propagation of the striped catfish was first done in late 1978 (Xuan, 1994). However, the results were not sufficiently reliable for mass seed production and the research activities were discontinued. Then research on induced spawning of striped catfish re-commenced in 1995 under an EU funded project, with the involvement of four partner organisations from France and Vietnam, which was led by Can Tho University (Phuong and Oanh, 2010). This research led to the development of techniques for the induced spawning of the striped catfish in 1996, and transferred to hatchery operators in 2000 (Cacot, 1999; Cacot et al., 2002). This initial development was followed by further improvements in the hypophysation technique on striped catfish, thereby consolidating the processes (Legendre et al., 2000; Manosroi et al., 2004). Since then, seed production of the striped catfish has increased significantly, currently fulfilling industry demand. 16.2 Striped catfish seed production: induced breeding in hatcheries Striped catfish seed production in Vietnam is structured within two main sectors-hatchery and nursery (Bui et al., 2010) (Fig. 16.4). Hatcheries produce large numbers of larvae which are mostly sold to nursery farms (94 %), while the nursery sector grows fry and fingerling for sale to the grow-out farms. 16.2.1 Hatchery design The size of hatchery depends on the target production of larvae, fry and fingerling. Based on the total larvae produced, the hatcheries are divided into three groups: ≤ 300 million fry/year (about 36.4 %); 300–500 million larvae/year (27.3 %); and ≥ 500 million larvae/year (36.4 %) (Le and Le, 2010). Bui et al. (2010) reported that the size of hatcheries varied from 0.2 to 15 ha (average 2.5 ha), with 0.05–10 ha (average 1.59 ha) under water. The area of hatchery houses varied from 120 to 500 m2. The larval production of hatcheries ranged from 10 to 3500 million, of which approximately 94 % were sold at larval stage (prior to commencement of feeding) to nursery farms (Fig. 16.5). Hatcheries are generally designed with four main components: broodstock tanks, hatching jars (Zoug jar and Weiss shaped incubators) (Fig. 16.6), larval handling tanks and broodstock ponds (including potential and conditioning ponds). The hatching jars have a volume of 6–200 L (average 40 L). The total hatching jar volume of the hatchery reflects the production © Woodhead Publishing Limited, 2013 502 Advances in aquaculture hatchery technology Hatchery sector Broodstock ponds Gametes Hatchery (incubation: 12–20 h) Nursery sector Larvae 94 % Larvae 6 % Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Earthen fry ponds (20–45 days) Earthen fry ponds (20–45 days) fry fry fry fry Earthen nursery ponds (20–120 days) Earthen nursery ponds (20–120 days) Grow-out sector On-stream and on canal ponds (5–6 months) fingerlings fingerlings Fig. 16.4 Structure of the hatchery and nursery sectors of the striped catfish seed production in the Mekong delta and the movement of stock between each sector (from Bui et al., 2010). Fig. 16.5 Hatchery and broodstock ponds. (Photo DN Long) © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Developments in hatchery technology for striped catfish 503 Fig. 16.6 Weiss shaped incubators. (Photo DN Long) capacity. According to Bui et al. (2010), the production of larvae varied from 1.8 to 3.8 million/L incubator/year. It is estimated that there is a total of 172 hatcheries and 5775 nurseries operating in the Mekong Delta, including ‘backyard’ hatcheries. The latter are simple and generally cater to needs of a single farmer with an integrated hatchery, fry to fingerling and grow-out facilities. However, the great bulk of seed production occurs in facilities that are dedicated for this purpose. Most hatcheries maintain large number of potential brood fish (varying from 350 to 29 200), but only a small proportion of this stock is used for breeding in a year. Therefore, many hatcheries have large areas of potential and conditioning broodstock ponds. The need to maintain such large numbers of potential broodstock, at a relatively high maintenance cost, which has been the tradition, has been questioned. The recently developed guidelines on ‘Better Management Practices’ for the catfish farming sector recommend that for an average hatchery operation to be successful the number of potential broodstock maintained could be around 200 (De Silva et al., 2011). 16.2.2 Broodstock sourcing Broodstock sources include pond (domesticated) and wild collected. Le and Le (2010) found that 78.1 % of hatcheries were using domesticated broodstock (collected from grow-out ponds), 6.3 % using wild-collected broodstock and 15.6 % using both sources. There is a clear trend towards in the increased use of pond reared broodstock. Belton et al. (2010) reported in detail on broodstock procurement and concluded that broodstock could be sourced from extensive grow-out, export-orientated grow-out, capture © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 504 Advances in aquaculture hatchery technology fisheries, own hatcheries or other hatcheries, in that order of importance. Bui et al. (2010) reported that male and female broodstock (including potential broodstock) should be from 0.5–8 kg and 0.5–12 kg in weight (average 3–6 kg), respectively. The age of fish at breeding should be over three years (normally five to six years). Broodstock are stocked at a rate of 5 t/ha (varying from 4 to 6 t/ha). The best stocking density is considered to be 4–5 t/ha. Males and females can be maintained at the ratio of three to four females to six to seven males, either separately or together. Broodstock selected for induced spawning must weigh at least 1.75 kg for females and 1.5 kg for males. Broodstock are generally discarded when they reach 10 kg or when the relative productivity (number of viable eggs produced) is less than 5 % of the female weight. Hatcheries normally recruit new broodstock on a regular basis of every two to three years; new broodstock are obtained both from grow-out farms and the wild. The replacement and procurement of fresh broodstock are currently done on an ad hoc basis and based entirely on the farmers’ experience/intuition. This is an area that needs much scientific input to ensure genetic diversity is maintained. 16.2.3 Broodstock conditioning and maturation culture Broodstock culture systems Broodstock are cultured in earthen ponds. Normally, hatcheries have many potential broodstock ponds and a smaller number of conditioning and maturation culture ponds (Fig. 16.7). On average, about eight (range 3–25) ponds are used for maintaining the large number of potential broodfish. The ponds are around 0.16 ha (from 0.02–3.0 ha) and 3–4 m deep. Fig. 16.7 Broodstock potential and conditioning ponds. (Photo DN Long) © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 505 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Broodstock ponds are carefully treated before use, usually by drying, sludge removal, liming (quick lime) and salting (common salt). Ponds are re-treated yearly or biannually. Most hatcheries use a river or canal as the main water source. Less than 50 % of farms screen the inlet water, but most farms treat the water once ponds are filled (Bui et al., 2010). The pond water is exchanged at around 10 % during the days of high tide (six to eight days/ month) during the conditioning culture period, and is exchanged daily up to 20–30 % during the maturation culture period. Feed and feeding Both manufactured pelleted feed and farm-made feed are used for striped catfish broodstock, singly or in combination, the latter being used more as a conditioning diet. The formulation of farm-made feed is relatively simple, often comprising a combination of locally available ingredients such as sundried trash fish (20 %), fresh trash fish (40 %), rice bran (30 %) and vegetable (10 %) (Bui et al., 2010; Phuong, 2012). The overall feeding rates for broodstock range from 0.2–10 % body weight/day (average 2.8 %) and 0.2–25 % body weight/day (average 5.4 %) for manufactured pelleted feed and farm-made feeds, respectively (Bui et al., 2010). Phuong (2012) reported that the feeding rates for broodstock vary according to the culture period; fish are fed 4–5 % body of weight for the preparatory period, and 1.5–2 % for the maturation and spawning periods. 16.2.4 Maturity and spawning season The striped catfish can reach full maturation in captive conditions and can be induced to spawn (CAB International, 2006). The fish spawns throughout the year, but the peak breeding period is in May–July (as in nature), which corresponds to the onset of the rainy season (Bui et al., 2010). Good quality broodstock from potential broodstock ponds are normally selected, based almost entirely on farmer experience, and transferred to maturation ponds for induced spawning about two to three months prior to spawning. 16.2.5 Hormone treatment and gametes collection Broodstock selection Principally, the selected females and males must be healthy, without visible injury or abnormal signs. The females should have a big belly, thin abdominal skin, swollen, reddish genitals and well-developed ovarian follicles (Fig. 16.8). However, sexual dimorphism is not clearly evident externally; therefore monitoring oocyte development using an intra-ovarian biopsy with a flexible catheter is often employed to evaluate the maturity state (Fig. 16.9). Well-matured broodstock should have an oocyte diameter of 1.0–1.1 mm, © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 506 Advances in aquaculture hatchery technology Fig. 16.8 Selection of broodstock for induced spawning basing on external appearance. Fig. 16.9 Checking oocyte of broodstock using a flexible catheter. (Photo DNLong) and the males should discharge milt on application of gentle pressure on the abdomen. Hormone injection There are several hormones and stimulating agents used to induce the spawning in striped catfish, e.g. hCG (human chorionic gonadotropin), ovaprim and pituitary gland. However, hCG is most commonly used because of its proven high efficacy. hCG is injected in females at doses of 200– 6500 IU/kg at a time and may be injected up to four or five times before © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 507 the fish are finally induced (Bui et al., 2010). However, the injection can be two or three times in the peak spawning season and three or four times in the offseason. In practice, the total doses of hCG vary from 5500 to 6500 IU/ kg. The males receive only one injection of 1000 IU/kg, coinciding with the time of the third injection for the females (Fig. 16.10 and Table 16.1). Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 16.2.6 Egg and sperm collection, fertilisation and incubation Ovulation occurs around 10 hours after the last injection. Eggs are collected as soon as possible by stripping (Fig. 16.11), because the survival time of eggs is short. According to Campet et al. (1999), the proportion of deformed larvae increased (24 %) and the hatching rate declined (35 %) if Fig. 16.10 Hormone injection for broodstock. Table 16.1 Hormone (hCG) dose rates and timing of hormone injection used to induced spawning in the striped catfish Female Male Injection No. Time (hr) 1st 2nd 3rd 4th Combined 0 8–24 16–18 24–72 Dose (UI/kg) Injection No. Time (hr) Dose (UI/kg) 200–2000 (542) 200–2000 (597) 200–2000 (893) 800–6500 (3442) 3000–8150 (5400) 1st 20–48 167–3500 (1060) Note: Values in parentheses are the mean. Source: Modified after Bui et al., 2010. © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 508 Advances in aquaculture hatchery technology Fig. 16.11 Stripping eggs. Fig. 16.12 Collection of sperm by syringe. (Photo Cacot) the eggs were collected 3 h after ovulation. Derivaz et al. (2000) also recognised that 4 h after ovulation, the proportion of normal larvae was reduced by half. The average relative fecundity of striped catfish is 150 000 eggs/kg female. Milt is collected into an immobilisation solution (containing 10 g TrisHCL in 1 L of 9 ppt water or physiological solution) container by pressing gently on the abdomen of the fish or using a syringe (Fig. 16.12). The milt is diluted five times in immobilisation solution for direct use or temporary storage at 4–5 °C for 24 h. A dry fertilisation method is normally used for the striped catfish, when eggs and milt are mixed gently. Fertilisation solution (containing 3 g urea and 4 g salt in 1 L of water) is added to the mixture of eggs and milt to © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 509 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 trigger fertilisation after 5 min. The fertilised eggs are then treated with tannic acid solution of 1‰ with a ratio of 1 : 1 (one volume of eggs and one volume of tannic acid solution) for 5–10 s. The fertilised eggs are then transferred into Zoug Jars or a Weiss incubation system. The incubators have a volume of 6 L or 40 L and are stocked at 0.23 kg eggs/L (varying 0.02–1.5 kg eggs/L). Fertilisation and hatching rates vary between the peak and off-season production periods. The fertilisation rates vary from 10–99 % (averaging 86 %) and 28–95 % (averaging 71 %); and the hatching rates are 60–100 % (averaging 88 %) and 50–100 % (averaging 77 %) during the peak and offseason production periods, respectively (Bui et al., 2010). 16.3 Striped catfish seed production: larval and fry nursing The larval rearing can be a part of the hatcheries but, in most cases, larvae are nursed to fry and fingerling stages by a nursery sector, which is separated from the hatchery activities. The commercial nursing of larvae-to-fry and fry-to-fingerling is done in earthen ponds to avoid mass mortality, because of the cannibalistic nature of the fish during the first week post-hatching. 16.3.1 Nursery pond construction The nursery ponds are located at on-stream and on-canal sites, to facilitate water exchange and ease of transportation of fry and fingerlings. The most popular pond shape is rectangular with a length to width ratio of three : four, an area of 1000–5000 m2 and a water depth of 1.5–2 m. The inlet and outlet usually have a diameter of 20–40 cm depending on the pond size and are located at the opposite sides of the ponds. 16.3.2 Pond preparation Nursery ponds for larval to fry rearing are prepared about a week before stocking to encourage the growth of live food. The pond preparation includes the removal of bottom sludge, liming 10–15 kg/100 m2, drying the pond bottom for three to five days and killing all unwanted organisms. In cases where the ponds cannot be completely drained, the use 0.5–1 kg/100 m2 derris root (Derris elliptica) containing rotenone or saponin products of 1 kg for 300–500 m3 should be effective to kill all unwanted organisms. The water supplied into the pond must be of high quality (such as pH from 6.4–8.5, dissolved oxygen ≥ 3 mg/L, free of toxicants). The water is screened by a fine mesh to prevent the entrance of eggs and larvae of other undesirable organisms. The water in the pond is levelled up to 1 m and © Woodhead Publishing Limited, 2013 510 Advances in aquaculture hatchery technology commonly treated with chlorine (1 kg/1000 m3) or formalin (25 mg/L). However, chlorine is most commonly used because of the lower cost. Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 16.3.3 Larvae to fry nursing Larvae of the striped catfish are cannibalistic, usually causing low survival rate during the first days of the nursing period. Low stocking density and creation of natural food in rearing water are very important to reduce this mortality. Pond fertilisation The nursing pond must be prepared well to permit the growth of natural food by adding fertiliser 24 h after treatment. This is important for the fish larvae in the first days of post-stocking. Fish powder (or low value fish meal) (2–3 kg), soybean meal (2–3 kg) or other products (such as Zeofish 4 kg + 1 kg blood powder DP92, or super benthos 6–8 kg) can be added into 1000 m2 of pond. In addition, supposedly beneficial bacterial products (or microbial-products) can be added into the pond at a rate of 300 g/1000 m3, together with 1–2 kg of live food (such as Moina). It should be pointed out that explicit scientific evidence is not available at present to indicate the beneficial effects, if any, of the addition of commercial products as such Zeofish, etc., which are readily available in the market and very aggresively marketed. Nevertheless, most farmers tend to use such products, incurring high costs in spite of the lack of scientific evidence of the claimed benefits. Stocking The larvae of the striped catfish have to be transferred to rearing tanks or ponds within 24 h after hatching and fed live food (Fig. 16.13). Good quality Fig. 16.13 Collection of larvae after hatching. © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 511 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 larvae usually have no abnormal signs, are of uniform size, swim actively and respond to external stimuli quickly. The stocking density of larvae in ponds varies from 500 to 800 larvae/m2. However, Bui et al. (2010) reported that the stocking density of larvae was highly variable among farmers and ranged from 250 to 2000 larvae/m2 (average 863 larvae/m2). Larvae are transported from hatcheries to nursing ponds in oxygenated bags (5000– 8000 larvae/L of water) in the early morning (7:00–10:00 am) or late afternoon to avoid direct exposure to sunlight. The larvae are acclimated to rearing pond water by keeping the bags in the pond for 15–30 min before releasing. First feeding The striped catfish larvae commence exogenous feeding two days after hatching (or 48 h) even when the yolk is not completely absorbed and the digestive tract is still not fully functional; at this time, the larvae require live food organisms for optimal growth and development (CAB International, 2006). In tank conditions, Artemia nauplii, Moina and Tubifex are usually fed to the larvae at a high feeding rate combined with slight aeration. However, in pond conditions, pond fertilisation to stimulate the growth of natural food together with the additional stocking of zooplankton and zoobenthos species (such as Moina, Artemia, Tubifex) are important to enhance the survival rate of the larvae. Hung et al. (2002) and Jacques et al. (1999) reported that Artemia is an excellent starter food for striped catfish, and gives the best growth performance. The feeding schedule for larvae to fry nursing is given in Table 16.2. Pond management Water quality and larval behaviour need monitoring/checking early every morning. Water colour should be maintained green (similar to banana leaf colour). Presence of predators such as snakes, frogs and carnivorous fish, insects etc. should be regularly checked and all precautions taken to prevent/ minimise their entry into ponds. The use of a light at the pond surface in the evening to gather harmful insects (such as Notonecta and dragonfly larvae), a net fence to prevent entry of frogs and scooping out tadpoles from the water surface must be regularly carried out during the nursing period. Overfeeding should be avoided to prevent deterioration of water quality. However, microbial-products such as EM, Bio-Tab, Zeofish, yucca can be administered weekly to enhance water quality. The application of lime (such as dolomite or CaMg(CO3)2, CaCO3) at the rate of 3–5 kg/100 m2 pond is required after heavy rain. The larvae metamorphose to fry (3000–4000 fry/kg) 20–45 days poststocking. Fry can be graded and transferred to other ponds for nursing to fingerling size (Fig. 16.4). The survival rate of the larvae to fry varies from 30 to 50 %. © Woodhead Publishing Limited, 2013 512 Advances in aquaculture hatchery technology Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Table 16.2 Feeding table for the striped catfish larvae Descriptions Week 1st (*) Week 2nd (*) Week 3rd & later Feeds Farm-made feed, which is formulated from soybean meal or fish meal (250 g), fish milk product (250 g), protein yeast (NuPro®) (50 g) and Bio-Mos (1 g) The mentioned amount is for 1 feeding Concentrated powder (40 % protein): 0.5 kg and nutritional products (50 g Nupro + 1 g Bio-Mos) for each feeding Commercial pellet (30–35 % protein) with instruction for feed size according to larval age with addition of Bio-Mos 2 kg/ton of feed and vitamin C (1–2 kg/ton of feed) According to the instruction of feed manufacturer Feeding rate Feeding frequencies Feeding methods Five feedings: at 7 h, 10 h, 13 h, 16 h and 19 h Mixing mixture with water and spraying over the pond surface The mentioned amount is for 1 feeding and is increased 10–15 % daily Four feedings: at 7 h, 11 h, 15 h and 19 h Mixing mixture with water and spraying over the pond surface Three to four feedings a day Soaking Bio-Mos, NuPro in water for 15 min then spraying onto commercial pellet before feeding the fish *Calculated for 1 million stocked larvae. 16.3.4 Fry to fingerling nursing Nursing of fry to fingerling is conducted in earthen ponds. Normally, nursery farms have ponds for both nursing fry and fingerlings, which have similar characteristics. Fry of 20–45 days are harvested and transferred to fingerling nursing ponds within a farm, or sold to other nursery farms. Stocking density The stocking density of fry varies from 200 to 300 ind./m2; fry should be in good health, indicated by active swimming and no signs of disease and/or injury, and of uniform size. The survival rate of the fry to fingerlings ranges from 40 to 50 %. Feed and feeding Fry are fed manufactured pelleted feeds containing 30–45 % crude protein according to size. The feeding rates vary from 6 to 8 % body weight with two or three feedings daily (Phuong, 2012). Nutrient supplements such as vitamin C (1–2 kg/t of feed) and Bio-Mos (2 kg/t of feed) are regularly used during the nursing period. © Woodhead Publishing Limited, 2013 Developments in hatchery technology for striped catfish 513 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 16.3.5 Larvae to fingerling nursing Nursing of larvae to fingerling is also conducted in earthern ponds. The nursing procedures are similar to those used for nursing larvae to fry and fry to fingerling. However, the average stocking density is 724 ind./m2. The nursing period is 2.72 months (varying from 2.5 to 3 months). The average survival rate is around 16.6 % depending on season, 15–20 % in the peak season (March–May) but only 5–7 % in the remaining months . 16.3.6 Economic aspects of fry and fingerling production In general, and similar to many cultured species, there is very little published data on the economics of fry and fingerling production. However, Le and Le (2010) studied the economic aspects of both larvae production and larvae to fry and fingerling rearing for catfish in the Mekong delta. Tables 16.3 and 16.4, respectively, give details on each of the above. The information in these tables confirms that there are many cost factors in these operations, and also provides further insights into each of the operations. For example, it is evident from Table 16.3 that most females are spawned more than once in a year with the best mean net income obtained when females were spawned five or six times. Similarly, in larvae to fingerling rearing the best net income was achieved when water was exchanged every five days with stocking densities of 500–700 m2 (Table 16.4). Table 16.3 Factors affecting the yield (fry production) and net income for catfish hatcheries Variable Unit Total volume of Weiss tank <100 L 100–200 L 200–300 L >300 L Fish yield Net income Mean ± SD Mean ± SD Million fry/L VND million/L/yr 3.1 ± 1.6 3.0 ± 3.3 3.8 ± 3.1 1.8 ± 1.0 6.3 ± 3.0 7.7 ± 4.2 8.2 ± 4.6 3.8 ± 3.3 Number of times of spawning per brooder/year ≤2 times 2.6 ± 0.9 3–4 times 1.9 ± 1.3 5–6 times 5.3 ± 3.6 ≥7 times 4.2 ± 3.5 Note: 18 000 VND = 1 US$ Source: Modified from Le and Le, 2010. © Woodhead Publishing Limited, 2013 5.2 ± 1.8 5.7 ± 4.1 9.3 ± 5.1 7.3 ± 4.5 514 Advances in aquaculture hatchery technology Table 16.4 Factors affecting the yield, production costs and net income of nursery rearing of striped catfish Variable Fish yield Production costs Net income Mean ± SD Mean ± SD Mean ± SD 1000 mil. fingerlings/1000 m2 pond/cycle VND mil./1000 m2 of pond area/cycle VND mil./1000 m2 of pond area/cycle Water depth of the nursery pond ≤1.5 m 75.0 ± 44.5 1.5–2.0 m 119 ± 76.1 2.0–2.5 m 128 ± 65.3 ≥2.5 156 ± 97.3 10.4 ± 7.6 16.5 ± 10.9 11.6 ± 8.4 11.9 ± 6.0 9.9 ± 12.2 41.1 ± 63.0 49.6 ± 48.8 18.3 ± 15.6 Frequency of water exchange Daily (1 day/time) 133 ± 78.5 3 days/time 87.6 ± 43.3 5 days/time 119 ± 63.4 7 days/time 137 ± 99.0 13.4 ± 9.20 13.5 ± 8.90 11.8 ± 6.70 13.8 ± 11.2 32.9 ± 41.3 37.1 ± 60.4 45.9 ± 64.3 22.3 ± 22.7 Stocking density of hatchlings ≤250/m2 63.9 ± 44.1 250–500/m2 111 ± 55.1 500–700/m2 116 ± 52.6 ≥750/m2 184 ± 103 13.4 ± 10.5 15.8 ± 9.9 11.8 ± 4.1 7.5 ± 2.8 34.5 ± 75.8 39.4 ± 50.0 45.5 ± 48.3 17.0 ± 13.8 Size of harvested fingerling (height) ≤1.5 cm 140 ± 96.5 1.5–2.0 cm 119 ± 69.5 ≥2.0 cm 103 ± 42.7 10.2 ± 4.6 14.3 ± 10.7 15.8 ± 10.4 20.1 ± 43.6 35.5 ± 44.1 51.9 ± 53.7 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Unit Note: 18 000 VND = 1 US$ Source: Modified from Le and Le, 2010. 16.4 Harvesting and transportation The harvest of fry and fingerling in ponds is done by seining. The ponds are normally disturbed in order to train the fish to adapt to transport conditions about three or four days before harvest. The seined fish are sorted in pond, with groups of uniform size fish kept in hapas (Fig. 16.14) before transferring to transportation facilities (bags or boats). The transportation of small fry is conducted in oxygenated plastic bags, while larger fry are transported in composite tanks with aeration (open transportation). The transport density of fry depends on size and duration, but it can range from 100 to 40 000 ind./L of water (average 7314) (Bui et al., 2010). The fish could be in transit for 6–25 h, and are normally treated with common salt prior to or during transport. The transportation of fingerlings to grow-out ponds is by boat with aeration (Fig. 16.15). The boats usually have a capacity of 20–30 t. Fingerlings © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 Developments in hatchery technology for striped catfish 515 Fig. 16.14 Conditioning fry in hapa before transportation. (Photo DN Long) Fig. 16.15 Boat used to transport fry and fingerling. are stocked at a density of three fish/L for fingerlings of 30–33 g, and 6–6.5 fish/L for fingerlings of 14–16 g. The water is exchanged 20–30 % every 6 h during transport. 16.5 Future trends The demand for striped catfish seeds will increase in the coming years to keep pace with the increase in nationally planned production. The induced spawning technique of the striped catfish is relatively well developed and © Woodhead Publishing Limited, 2013 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Phuong-Thanh Nguyen (435-03-347) Sunday, August 04, 2013 8:49:26 AM IP Address: 113.169.163.26 516 Advances in aquaculture hatchery technology is being gradually improved in order to obtain a higher productivity and a better larval, fry and fingerling quality. However, each of the stages in the cycle needs improvement, mortality needs to be reduced at each stage and costs need to be rationalised. Hence further research is needed. Research is being conducted on broodstock source selection and management, broodstock feeds, hormone and stimulating agents to induce spawning and genetic improvement for enhancing growth performance. Research is needed in the coming years to develop genetic improvement for specific disease resistance and saline water tolerance. Research on nursery techniques has also been planned to improve the quality and survival rate at different nursing stages (larvae to fry and fry to fingerling) by improving compound feeds and live feed generation in ponds. As pointed out previously, most farmers are encouraged to use substances and compounds purporting to enhance/improve production through reduced mortality, disease occurrence, etc. These treatments and substances impose substantial costs to farmers, yet the inefficacy has not been proven, and research in this regard is urgently needed, especially so the catfish farming sector can maintain long-term economic viability. 16.6 References baran e (2006) Fish migration triggers in the Lower Mekong Basin and other tropical freshwater systems, MRC Technical Paper No. 14. Vientiane: Mekong River Commission. belton b, little d c and le x sinh (2010) Pangasius catfish seed quality in Vietnam. Part 1. User and producer perceptions on broodstock and hatchery production. Aquaculture Asia, March–April, 36–39. bui tam m, phan lam t, ingram b a, nguyen thuy t t, gooley g j, nguyen hao v, nguyen phuong v and de silva s s (2010) Seed production practices of striped catfish, Pangasianodon hypophthalmus in the Mekong Delta region, Vietnam. Aquaculture, 306, 92–100 cab international (2006) Case study: Artificial seed production of Pangasiid catfish in the Mekong Delta, Vietnam, Aquaculture Compendium 2006. Wallingford: CABI. cacot p (1999) Description of the sexual cycle related to the environment and set up of the artificial propagation in Pangasius bocourti (Sauvage, 1880) and P. hypophthalmus (Sauvage, 1878) reared in floating cages and in ponds in the Mekong Delta, in Legendre M and Pariselle A (eds), The Biological Diversity and Aquaculture of Clariid and Pangasiid Catfishes in South East Asia. Proceedings of the mid-term workshop of the ‘Catfish Asia Project’ Cantho, Vietnam, 11–15 May 1998. 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Supply and use of catfish (Pangasianodon hypophthalmus) seed in the Mekong delta of Vietnam. Aquaculture Asia, January–March, 27–32. lefevre s, huong d t t, wang t, phuong n t and mark b (2011) Hypoxia tolerance and partitioning of bimodal respiration in the striped catfish (Pangasianodon hypophthalmus). Comparative Biochemistry and Physiology, Part A, 158, 207–214. legendre m, slembrouck j, subagja j and kristanto a h (2000) Ovulation rate, latency period and ova viability after GnRH- or hCG-induced breeding in the Asian catfish Pangasius hypophthalmus (Siluriformes, Pangasiidae). Aquatic Living Resources, 13, 145–151. manosroi j, meng-umphan k and manosroi a (2004) Maturation induction of Pangasius hypophthalmus using gonadotropin releasing hormone analogue (GnRHa) in combination with domperidone, in oil suspension dosage. 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Phnom Penh: Mekong River Commission. xuan t t (1994) Some biological characteristics and artificial reproduction of river catfish (Pangasus micronemus Bleeker) in the South Vietnam, International Workshop on the Biological Bases for Aquaculture of Siluriformes, May 24–27, Montpellier. © Woodhead Publishing Limited, 2013