Techniques in finfish larviculture

Techniques in finfish larviculture in Taiwan
I Chiu Liao a,), Huei Meei Su b, Emily Y. Chang a a Taiwan Fisheries Research Institute, 199 Hou-Ih Road, Keelung 202, Taiwan b Tungkang Marine Laboratory, Taiwan Fisheries Research Institute, Tungkang, Pingtung 928, Taiwan
Abstract
Taiwan now has over 90 finfish species in which larviculture is possible. Billions of finfish fry can be produced annually. The use of modern and advanced techniques in larviculture has won Ž. Taiwan a leading position in the world. This achievement can be attributed to: 1 successful broodstock management, including broodstock collection and cultivation, maturation and spawnŽ. ing, and egg collection and incubation, 2 complete larval rearing using outdoor and indoor Ž. systems, and 3 establishment of techniques of live food preparation for larval feeding. Cannibalism, difficulties in water quality control, and disease outbreak often cause mass mortality in the rearing larvae. However, the obstacles that hinder the development of larvae at their later stages are being overcome. Through a systematic understanding of the complex behavioral patterns of finfish larvae, cannibalism can somewhat be controlled under larviculture conditions. Control strategies often involve physical manipulations such as grading and feeding adjustments. For water quality and disease control, an indoor larval rearing system has recently been established. It adopts ozone or chlorine to disinfect fertilized eggs, the rearing water, and facilities. Additionally, utilization of the green water technique in rearing larvae and of ozone-disinfected recirculating water in weaning larvae has improved the hygiene of the systems. For instance, the average survival rate in the fry of grouper used to be less than 0.1% until they attained a size of about 2 cm. With the improved system, grouper fry grow from 3 to 10 cm with almost no mortality or viral infection, with a feed conversion rate of 0.7–0.9 and a daily weight increase rate of 4–27%. Application of live food enrichment techniques with selected nutrients for short and long terms has proven beneficial to larval growth. Studies determining the optimal environmental requirements of larvae have been essential towards successful larviculture. This paper mainly discusses
) Corresponding author. Fax: q886-2-2462-4254. Ž.E-mail address: icliao@mail.tfrin.gov.tw I.C. Liao .
0044-8486r01r$ - see front matter q2001 Published by Elsevier Science B.V. Ž.PII: S 0044-8486 01 00692-5
()I.C. Liao et al. rAquaculture 200 2001 1–312
developments and advanced techniques of finfish larviculture in Taiwan. q2001 Published by Elsevier Science B.V.
Keywords: Techniques; Finfish; Larviculture; Taiwan
1. Introduction
The practices of finfish culture in Taiwan can be traced back to the 15th and16th Ž centuries when emigrants from mainland China came to settle on the island Liao, . 1993 . Techniques of larviculture have gradually been developed from simply collecting the stocking material in the wild, to holding them for further use, to growing them in a pond, and to using modern, advanced facilities and treatments for complete larviculture practices. In Taiwan, it was not until the early 1960s that modern techniques in larviculture began to evolve. A major success was the establishment of techniques for Ž.freshwater finfish propagation in grass carp Ctenopharyngodon idellus and silver carp Ž . Ž . Hypophthalmichthys molitrix Liu, 1963, 1964; Tang et al., 1963; Lin, 1965 . Following that, propagation techniques for marine finfish were established for grey mullet, Ž.Mugil cephalus Liao et al., 1969 . With techniques developed for these species as the Ž benchmark, larviculture for over 90 finfish species is now possible in Taiwan Table 1a . and b . Many fisheries resources and wild fry have been seriously depleted due to overfishing and environmental pollution. The availability of quality seedstock has been one of the most critical factors in the commercial success of industrial production of finfish that has stimulated continuous developments of finfish larviculture in Taiwan. In other parts of the world, large-scale production of marine finfish fry began in the 1980s and has Ž. continued onwards Sorgeloos et al., 1995 , During this time, Japan pioneered the red Ž.sea bream Pagrus major and Europe developed the most competitive hatchery Ž . Žmethods for the sea bass Dicentrarchus labrax and the gilthead sea bream Sparus .aurata . To assure a steady protein supply and good quality aquatic food for human consumption, reliable and sound techniques in larviculture have become essential in aquaculture now and for the future. A complete finfish larviculture generally involves three phases of techniques, includŽ . Ž . Ž . ing 1 broodstock management, 2 larval rearing, and 3 food preparation. Broodstock management involves techniques to collect and culture high quality broodstock, to induce maturation and spawning, to manipulate sex, to preserve sperm, and to collect and incubate eggs. In larval rearing, techniques that have been developed concern the larviculture system, nutrient requirements, cannibalism prevention, and pond management. Nutritional content and size of food for larvae and fry determine the success of commercial-scale larviculture. Food preparation for larviculture involves the use of Ž. highly unsaturated fatty acids HUFAs -supplemented feeds, the application of suitable live food for different larval stages, and the adoption of live food enrichment protocols. Each time problems occur during the course of research and development of finfish fry production in one target species, techniques applied to all these three phases must be evaluated and modified. This paper describes techniques that have been successfully
()I.C. Liao et al. rAquaculture 200 2001 1–31 3
developed and are continuously being applied to finfish larviculture in Taiwan, specifiŽ . Žcally using freshwater finfish, milkfish Chanos chanos , groupers, cobia Rachycentron . Ž .canadum , and eel Anguilla japonica as examples.
2. Broodstock management
The purpose of broodstock management is to supply good quality eggs and larvae. It generally covers the collection and domestication of broodstock, maturation and spawning, and egg collection and incubation.
2.1. Collection of broodstock
A successful hatchery operation is based on healthy broodstock. Broodstock are usually caught from the wild, bought from commercial grow-out ponds, or raised in the hatchery for artificial propagation purposes. Different species require different ways of collection and cultivation. In the past, broodstock of grey mullet were captured from the wild during their spawning migration. Spawners of grey mullet were caught using an outboard-powered raft, then brought into indoor tanks and immediately induced to Ž. spawn by hormonal treatment Liao et al., 1972; Liao, 1975 . Milkfish broodstock, on the other hand, are rarely caught from the wild or are not available from commercial grow-out ponds because at market size milkfish are generally too young for induced maturation. Milkfish do not become sexually mature until many years after reaching the market size. Therefore, young milkfish are usually raised in the hatchery’s grow-out Ž. ponds, which may take at least 5 years Liao and Chen, 1979 . For grouper fry production, collection of broodstock is the first bottleneck because the mature fish are quite expensive and less available in captivity. Fish of maturing age are difficult to obtain in large numbers. Groupers are protogynous hermaphrodites, being female in their early life and turning into male at older ages, so that the males are usually larger in size and rare in the population. Broodstock can be obtained from the wild or from ponds, where young groupers are reared until sexual maturity. Pond-reared broodstock have better survival rate and breeding performance than wild-caught broodstock.
2.2. Feeds
To assure good quality eggs, dietary lipid composition in broodstock feed is important. The quality and quantity of ny3 HUFAs contained in fish feeds may Ž influence development of the gonads and quality of the egg Navas et al., 1998; Sargent . et al., 1999 . Recent studies have concentrated on the lipid content of feeds for Ž.broodstock. Broodstock of seabass D. labrax that had insufficient feed or diet Ž. produced poor quality eggs with a low fertilization rate Katavic, 1986 . In Taiwan, Ž broodstock of carnivorous fish are generally fed with fresh trash fish mostly Scomber .australasicus . Fresh trash fish has recently been found to improve gonadal develop
()I.C. Liao et al. rAquaculture 200 2001 1–314
Table 1 Ž . Ž . a List of freshwater finfish larvicultured in Taiwan modified from Liao, 2000
Scientific name Common name Year of first success
Aristichthys nobilis Bighead carp 1963 Bidyanus bidyanus Silver perch 1994 Carassius auratus Gold crucian carp – Channa maculata Snakehead 1970 Cirrhina molitorella Mud carp 1963 Clarias batrachus Thailand catfish – C. fuscus Walking catfish 1970 Colossoma macropomum Pacu 1984 Ctenopharyngodon idellus Grass carp 1963 Culter erythropterus Redfin culter 1974 Cyprinus carpio Common carp – Hypophthalmichthys molitrix Silver carp 1963 Lates calcarifer Giant perch 1983 Lateolabrax japonicus Japanese sea bass 1982 Leptobarbus hoeÕenii Sudan fish 1984 Megalobrama amblycephala Wu-Chang fish 1982 Micropterus salmoides Largemouth bass 1983 Misgurnus anguillicaudatus Pond loach 1977 Morone saxatilis=M. chrysops Hybrid striped bass 1995 Mylopharyngodon piceus Black carp 1966 Onchorynchus mykiss Rainbow trout 1964 Oreochromis aureus Blue tilapia 1975 O. mossambicus Mozambique tilapia 1946 O. mossambicus=O. niloticus Fu-So tilapia 1969 Oreochromis niloticus Nile tilapia 1967 O. niloticus=O. aureus Hybrid tilapia 1974 Oxyeleotris marmortus Marble goby 1973 Pangasius sutchi Thailand catfish 1976 Parasilurus asotus Chinese catfish 1971 Ple