Intensive rearing techniques and feeding behaviour of larval and juvenile mulloway, Argyrosomus japonicus

Ballagh, Debra Anne (2011) Intensive rearing techniques and feeding behaviour of larval and juvenile mulloway, Argyrosomus japonicus. PhD thesis, James Cook University.

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Mulloway, Argyrosomus japonicus, is a euryhaline sciaenid that is popular with seafood consumers and recreational fishers. The species is an emerging aquaculture candidate and culture techniques have been developed. But with industry production low and fingerling costs estimated to be as high as $2 each, there is an imperative to improve production technology and lower costs. This study aimed to improve mulloway hatchery efficiency through:

• the development of specific disinfection protocols for mulloway eggs to reduce the potential for transmission of pathogens on the surface of eggs.

• an improved understanding of embryonic development.

• optimization of light and feeding regimes to increase growth and survival of larvae and juveniles.

• a better understanding of the biological mechanisms underpinning feeding behaviour for larval and juvenile stages.

Disinfection of fish eggs with ozone is an important practice to reduce the incidence of infection by pathogens in the hatchery. However, ozone can reduce hatching success and can induce deformities in hatched larvae. In this study, the embryonic development of mulloway was described in greater detail than previously available to create a visual reference of egg stages and to assist in the development of a safe ozone disinfection protocol. The potential impact of ozone exposure is measured using a CT value, which is the concentration of ozone (mg l-1) multiplied by the contact time (min). Initially, the combined effects of ozone CT (0, 0.1, 0.5, 1 or 5) and treatment temperature (19, 22 or 25°C) on the hatching success of mulloway larvae were evaluated. The highest CT value that did not negatively affect hatching was a CT of 1, and the most appropriate water temperature for disinfection was 22°C, as there were no apparent negative impacts of treating eggs at this temperature and mulloway eggs are currently incubated at 22°C at the Port Stephens Fisheries Institute (PSFI) hatchery. Embryos at four different stages of embryonic development (3, 8, 20 or 27 h post fertilisation; HPF) were then exposed to ozone (CT = 1) and no significant effect was detected on hatchability at any of the embryonic stages examined. Accordingly, it is suggested that eggs should be disinfected with ozone early in development to reduce negative impacts on development caused by nodavirus and other pathogens.

The photoperiod and light intensity requirements of early and advanced larvae were investigated to determine an appropriate light regime. Two experiments were conducted to investigate the effects of a range of photoperiods (24L:0D, 18L:6D, 12L:12D, 6L:18D or 0L:24D) and light intensities (1 or 10 μmol s-1 m-2) on the growth, swim bladder (SB) inflation, food consumption and survival of early (2-8 dah [days after hatching]) and advanced (14-34 dah) mulloway larvae. The two light intensities tested had no effect on the parameters measured in early or advanced larvae and there were no significant interactions between photoperiod and light intensity. In early larvae, the optimal photoperiod was determined to be 12L:12D, which promoted growth, survival and SB inflation. Once SB inflation has been achieved, the photoperiod should be adjusted to 18L:6D to increase feeding time and promote growth. In advanced larvae, no differences in growth were observed at the end of the experiment; however, survival was significantly better in the 0L:24D photoperiod compared with all other photoperiods examined. It is possible that there are physiological effects of maintaining larvae in complete darkness, and until further research is completed, it is recommended that an 18L:6D photoperiod is used. This protocol is expected to optimise growth and subsequently reduce the overall time that larvae remain in the hatchery.

The optimal weaning procedures for mulloway larvae were also investigated. Three experiments were conducted to compare weaning strategies using live feeds; rotifers (Brachionus plicatilis) and Artemia, and formulated pellet diets. Initially, the effects of feeding Artemia at different levels (0, 50 or 100% ration of Artemia fed from 18 dah [days after hatching]; based on current hatchery protocols) and a pellet diet from two larval ages (14 or 23 dah) were investigated. Results indicated that some Artemia should be in the diet of larvae to promote growth; however, it is possible to feed half the usual amount without reducing growth rates. Growth of larvae was not influenced by the time of pellet introduction. The size (total length [TL]) at which mulloway larvae selected Artemia equally or in preference to rotifers, and pellet (400 μm) equally or in preference to Artemia, respectively was then determined. The mean size (± SEM) at which mulloway larvae began selecting Artemia equally to rotifers was 5.2 ± 0.5 mm TL and selected pellets equally to Artemia at 10.6 ± 1.8 mm TL. This has led to the establishment of weaning protocols for larval mulloway that optimise larval growth while reducing feed costs by minimising the amount of Artemia used during production.

Next, the optimal photoperiod and feeding interval requirements for rearing juvenile mulloway were examined. A two factor experiment incorporating three photoperiods (12L:12D, 18L:6D or 24L:0D), and five feeding intervals (1, 3, 6, 12 or 24 h between feeds) determined the effects on somatic growth rate, feeding efficiency and survival of juvenile mulloway (2.7 ± 0.5 g). The growth indices used included fish weight, length, food conversion ratio (FCR), condition factor (CF), and the coefficient of variation of weight (CVwt). No interactions were found for any parameters measured. The 12L:12D photoperiod produced significantly poorer survival than other photoperiods; however, feeding interval did not influence survival. It was determined that feeding can be optimised by rearing juvenile mulloway in an 18L:6D photoperiod and by feeding once every 12 h. The 24L:0D photoperiod reduced growth (weight and length) and increased the FCR, and the 12L:12D photoperiod reduced survival with the result that the fish in the 18L:6D photoperiod had optimal growth and survival parameters. The only feeding interval to affect growth (weight and length) was the 24 h feeding interval; there was no difference in growth detected between the 1, 3, 6, or 12 h feeding intervals. It was also determined that it would take 10 h for 50% of the feed consumed in one meal to be evacuated from the stomach. Given that there was no significant difference in growth and feeding efficiency in juvenile mulloway between the 1, 3, 6 and 12 h feeding intervals, it would be more efficient for producers to feed their fish no more than twice daily (or every 12 h). The increase in feeding efficiency associated with these feeding techniques is likely to increase production and reduce the time mulloway remain in the hatchery.

Finally, the sensory basis for feeding was investigated for larval and juvenile mulloway, including the contribution of vision, mechanoreception and chemoreception to the feeding ability of larval and juvenile mulloway. Firstly, an investigation into the ablation of the mechanosensory neuromasts using streptomycin sulphate (SS) determined that larvae exposed to SS at a concentration of 0.75 g l-1 for 3 h had a reduced startle response but did not exhibit abnormal swimming behaviour. The contribution of each sensory system to feeding was then examined for larval and juvenile mulloway between 3.5 and 53.3 mm. From 3.5 to 4.1 mm, mulloway larvae consumed significantly more live food items when fed in light conditions compared with those fed in dark conditions, indicating that vision was the primary sense mode used for feeding. From 5.0 mm, the mechanosensory system appeared to play an increasingly important role in feeding and it was observed that the number of live food items consumed was significantly greater when vision and mechanoreception were available until larvae reached 7.5 mm. Evidence of an increase in the contribution of the olfactory organs to feeding was also observed from 8.7 mm, while fish were feeding on live feeds. From 10.6 mm, fish were fed pellets and while fish were observed feeding in both light and dark conditions, feeding success became greater in fish fed in the light providing evidence that the role of vision was again the primary sense mode. This change in the contribution of the sensory organs to feeding as development proceeds in larval and juvenile mulloway is discussed.

The protocols developed in this thesis have now been adopted in practice at the PSFI and have improved growth and survival rates. The average production costs of juvenile mulloway reared at the PSFI is now estimated to be $1.05 per fingerling, and this is expected to have increased the viability of mulloway as an aquaculture species. In particular, the reduction of the quantity of Artemia required to rear larval mulloway has reduced by 50%, which is a significant saving in production costs. In addition, the protocols developed for ozone disinfection of mulloway eggs has been adopted for other species such as Australian bass (Macquaria novemaculeata), yellowtail kingfish (Seriola lalandi) and southern blue-fin tuna (Thunnus maccoyii). This thesis has also highlighted new research priorities for mulloway cultivation and has formed the basis of rearing protocols for yellowtail kingfish and southern blue-fin tuna, which are now under investigation to determine optimal culture techniques.

Item ID: 24344
Item Type: Thesis (PhD)
Keywords: aquaculture, Argyrosomus japonicas, mulloway, embryonic development, feeding regimes, light intensity, ozone disinfection, photoperiods, fisheries production technology, pathogens, infections, larval stages, hatchery, hatcheries
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Ballagh, D.A., Pankhurst, P.M., and Fielder, D.S. (2011) Embryonic development of mulloway, Argyrosomus japonicus, and egg surface disinfection using ozone. Aquaculture, 318 (3-4). pp. 475-478.

Chapter 4: Ballagh, Debra A., Fielder, D. Stewart, and Pankhurst, Patricia M. (2010) Weaning requirements of larval mulloway, Argyrosomus japonicus. Aquaculture Research, 41 (10). e493-e504.

Chapter 5: Ballagh, D.A., Pankhurst, P.M., and Fielder, D.S. (2008) Photoperiod and feeding interval requirements of juvenile mulloway, Argyrosomus japonicus. Aquaculture, 277 (1-2). pp. 52-57.

Date Deposited: 21 Dec 2012 04:57
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 34%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060803 Animal Developmental and Reproductive Biology @ 33%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070405 Fish Physiology and Genetics @ 33%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830102 Aquaculture Fin Fish (excl. Tuna) @ 34%
83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830199 Fisheries - Aquaculture not elsewhere classified @ 33%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 33%
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