Rimmer, Michael Albert (1996) Factors affecting survival and growth of larval barramaundi Lates calcarifer (Bloch) in aquaculture, with particular reference to feeding and extensive rearing. PhD thesis, James Cook University of North Queensland.

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Abstract

Early attempts to intensively rear barramundi, Lates calcarifer, larvae in Australia were periodically beset with problems of high or total mortalities. To determine whether these problems could be ascribed to deficiencies of polyunsaturated fatty acids in the live food organisms used for larval rearing, barramundi larvae were reared in an experimental system comprising replicate 2 litre plastic containers and fed on four diets, representing combinations of supplemented and unsupplemented rotifers (Brachionus plicatilis) and supplemented and unsupplemented brine shrimp (Artemia salina). Supplementation of rotifers and brine shrimp with a commercially available microencapsulated diet increased the levels of several polyunsaturated fatty acids in the food organisms. Two test diets using freshly hatched brine shrimp produced near total mortality by day 30, while the other two diets, using supplemented brine shrimp, produced negligible mortality over the same period. Supplementation of rotifers with microcapsules resulted in slightly increased growth, but also slightly decreased survival. A second experiment showed that starvation of brine shrimp prior to feeding delayed the onset of the mortality syndrome, but only supplementation with the microencapsulated diet prevented substantial mortalities within the rearing period.

Attempts to replace live prey organisms with microparticulate diets, in order to reduce the costs associated with intensive rearing of barramundi larvae, were unsuccessful. Barramundi larvae fed a microparticulate diet began dying 6 days after initiation of the experiment, presumably from starvation. Mortalities amongst a control group, fed supplemented brine shrimp, were negligible over the same period. Factors which appeared to contribute to the poor acceptance of the microparticulate diet by barramundi were the availability of particles in the water column, and perception of particles by the larvae.

Extensive larval rearing trials with barramundi in a 1350 m² brackishwater pond showed that this technique has numerous advantages over traditional intensive rearing methods. Pond productivity was enhanced by adding inorganic and organic fertilisers to promote 'blooms' of phytoplankton, bacteria and protozoans to provide food sources for zooplankton. Barramundi larvae were stocked into ponds the day after hatching (day 2) and grew to 21.5 - 40.8 mm total length in about 3 weeks; representing growth rates of 1.1 to 1.7 nun/day.

Survival of barramundi in extensive rearing trials ranged from 0 to 86% (mean 22%), and production (excluding those trials with survival <1%) ranged from 9,215 to 637,037 fish/ha and 0.05 to 7.1 kg/ha/day. Survival of barramundi in these larval rearing trials was found to be correlated with water temperature and pH during the first week after stocking larvae into the pond. Growth rate was correlated with fish length, fish age, degree days, water temperature, and air temperature.

The diet of barramundi larvae in extensive rearing ponds was examined to determine which types of prey were important as food sources. Barramundi showed a consistent pattern of dietary progression, initially feeding on rotifers and copepod nauplii, then changing to larger zooplankton (copepodites, copepod adults, and cladocerans) and finally to benthic organisms (chironomid larvae). This pattern was modified by the addition of aeration to the pond, when the larvae commenced feeding on copepod nauplii rather than rotifers.

The results of this research are discussed with a view to developing research strategies to improve the reliability and cost-effectiveness of larval rearing techniques for barramundi. Extensive larval rearing of barramundi has several advantages over traditional intensive rearing techniques, the most important of which is the lower cost of production of fingerlings. Consequently, extensive rearing techniques have been widely adopted by the barramundi aquaculture industry in northern Australia.

Item ID:	33791
Item Type:	Thesis (PhD)
Keywords:	aquaculture; Asian seabass; barramundi; diet; feeding; intensive rearing; juveniles; larvae; larval rearing; Lates; live food; mariculture; water quality
Date Deposited:	05 Sep 2014 06:48
FoR Codes:	07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 100%
SEO Codes:	83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830102 Aquaculture Fin Fish (excl. Tuna) @ 100%
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