Improved feeding and quality control for the ornamental fish industry in singapore-2001

PhD Thesis by Lian-Chuan Lim, Faculty of Agricultural and Applied Biological Sciences, Ghent University, Belgium

Summary:

Chapter II (The ornamental fish industry in Singapore) reviews the status of the ornamental fish industry in Singapore together with the operations of the export trade and farming industry, and identifies the key challenges and major issues of the industry. The major technical issues hindering the growth of the industry are the lack of suitable live food organisms for feeding at the various production stages, the low stress resistance of the fish and the high mortality at 7-day post-shipment, which form the rationale for the research objectives of this study.

Chapter III (Use of the rotifer, Brachionus calyciflorus Pallas, in freshwater ornamental fish larviculture) explores the application of the freshwater rotifer, Brachionus calyciflorus, as a starter food for two important freshwater ornamental fish species, Dwarf Gourami and Brown Discus. Dwarf Gourami is a typical freshwater ornamental fish species with small larvae that are too small to ingest Artemia nauplii or Moina at first feeding. Compared with the conventional yolk food, the rotifers used as starter food significantly improve the growth and survival of Dwarf Gourami larvae (Day 2-12). These beneficial effects are extended to the subsequent Artemia feeding phase (Day 13-32), suggesting that the quality of starter food is crucial to later development. In Discus, larvae are dependent on the body slime of their parents as a nutrient source during the first 2 weeks of exogenous feeding. Use of rotifers, followed by feeding with Artemia nauplii, facilitates artificial larviculture of the Brown Discus, and their larval growth and survival are comparable to those that rely on parental feeding. The artificial feeding would eliminate the risk of larvae being eaten by the parent fish and shorten the breeding interval of the spawners, thereby leading to higher yield of fry. This feeding protocol is less tedious and more practical than the existing strategies of smuggling the batch of larvae to foster parents or feeding the larvae with egg food.

Chapter IV (Use of decapsulated Artemia cysts in ornamental fish culture) evaluates the technical feasibility of using decapsulated Artemia cysts as a substitute for Artemia nauplii or Moina in freshwater ornamental fish culture. Results show that decapsulated Artemia cysts could be used as a substitute for Artemia nauplii or Moina in freshwater ornamental fish culture. The fry of all the five common ornamental fish species tested (Guppy, Molly, Platy, Swordtail and Neon Tetra) could readily feed on decapsulated cysts, and their performance in terms of stress resistance, growth and survival is comparable to or better than those feeding on Artemia nauplii or Moina. Apart from being a hygienic off-the-shelf feed, the direct use of the cysts signifies a new area of application for low-hatch cysts in the ornamental fish industry, with concomitant saving in the feed cost.

Chapter V (Production and application of on-grown Artemia in freshwater ornamental fish farm) describes a simple and cost-effective pilot culture system for the production of on-grown Artemia in freshwater ornamental fish farms. The system uses diluted artificial seawater for culture, and has a mean production rate of 3 kg/m³ of water in a 12-day cycle and a production capacity of 8 metric tons wet weight of on-grown Artemia a year. Cost-benefit analysis shows that with a capital investment of US$ 82,000 and an annual cost of production of US$ 81,000, the system achieves a high internal rate of return of 88% over a 10-year period and a short payback period of 1.23 years. With the system, farmers may produce any specific size of on-grown Artemia of up to 5 mm to suit the age and size of their fish, by varying the time of harvesting. This characteristic, coupled with the possibility to enhance the nutritional quality of the Artemia through bioencapsulation, makes on-grown Artemia an ideal organism to replace the unhygienic Moina or Tubifex in freshwater ornamental fish culture.

Chapter VI (A stress test for quality evaluation of Guppy, Poecilia reticulata Peters) reports the use of a simple and effective stress test for quality evaluation of the Guppy. The test entails exposure of the fish to osmotic shock in a single concentration of pre-aerated saline water over a 2-h period. While the stress resistance of the adult Guppy is higher than that of the 2-week old fry, there is no difference in the stress resistance among fish within the market-size range of 28-40 mm total length. The female Guppy is more resilient than male fish to salinity stress. The stress test is effective in differentiating the quality of Guppy in terms of their nutritional status, and to distinguish infected fish from the healthy ones, prior to the onset of disease symptoms. The stress resistance of Guppy could be enhanced through several stress resistance enhancement techniques. They include starving the fish for 1-2 days, holding in saline water at 3-9 ppt for 40 h, feeding with glutathione supplementation at 5,000-10,000 mg/kg diet for three weeks or with vitamin C at 2,000 mg/kg for 7 days. Except glutathione, the cost of which is prohibitive for field application, all the other three stress resistance enhancement techniques may have potential application in the ornamental fish industry.

The effect of nutritional prophylaxis by vitamin C supplementation is further demonstrated in Chapter VII (Enhancement of stress resistance of Guppy, Poecilia reticulata Peters, through feeding with vitamin C supplement). The stress resistance of Guppy could be enhanced through feeding either with formulated diets fortified with AA at 1,000 mg/kg or 2,000 mg/kg or with Artemia juveniles, even without vitamin C enrichment. Biochemical analyses show that raising the ascorbic acid level in feeds results in a concomitant increase in the incorporated ascorbic acid level in the whole-body tissues of the Guppy. The use of vitamin C supplement to enhance the stress resistance of Guppy has also been demonstrated in the commercial production of the fish.

In Chapter VIII (Reduction of post-shipment mortality of Guppy, Poecilia reticulata Peters, through enhancement of stress resistance), results of the fish packaging experiments demonstrate that stress resistance is a critical factor in the packaging of Guppy. Results show that starving Guppy for a day prior to transport or adding salt to transport water at 1-3 ppt followed by recovery in the respective salinity with daily dilution is effective in reducing the post-shipment mortality by 8% and 3-5% respectively. Feeding a vitamin C supplement at 2,000 mg/kg diet for 10 days prior to shipment significantly reduces the post-shipment mortality of Guppy from 23% to 8%. Vitamin C-feeding is also effective in enhancing the disease resistance of the fish infected with Tetrahymena, and results in significant reduction of the post-shipment mortality from 90% to 14%. Treatment of the infected fish with chlorine dioxide at 20 mg/l during transportation significantly cuts down the post-shipment mortality from 75% to 31%.

Chapter IX (Review on the ornamental fish packaging system for air transport) gives a review on the ornamental fish packaging system, based on bibliographical studies and the experience of the Singapore exporters. The review reveals that the current system is characterized by very high fish loading density and high ammonia and low pH in the transport water after shipment. The state-of-the-art of the packaging technology focuses mainly on the management of water quality parameters to reduce the stress imposed on the fish during transport, and there is insufficient attention to enhancing the stress resistance of the fish. As the effect of transportation of the ornamental fish actually goes beyond the actual transportation phase, emphases should also be placed on the preparation of fish for transport and the recovery of fish after shipment. In this context, farmers can contribute significantly by applying nutritional prophylaxis prior to harvesting and taking good care of the fish during the harvesting operation. Exporters may use the salinity stress test to identify fish lots of good quality for transport, apply health prophylaxis to eradicate parasites and practise the various stress resistance enhancement techniques in fish packaging. Importers can also adopt proper acclimation procedure and allow fish to recover in low salinity water with daily dilution. In order to cut down fish loss after shipment, the industry should consider revising the basis of the warranty system to their customers, from death on arrival (DOA) to 7-day post-shipment mortality (DA7).

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