Gamage, Kumudu Radampola (2001) The effect of nutrition on reproductive parameters in male barramundi, Lates calcarifer (Bloch). PhD thesis, James Cook University.

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Abstract

Fish reared in aquaculture must be provided with an adequate diet for growth and reproduction. Although there is a paucity of literature on broodstock nutrition generally, particularly for male fish, it is known that nutrition has profound effects on reproductive physiology. Most of the available information documents dietary effects on direct reproductive outcomes, such as fecundity, spawning performance, egg and larval quality. Information on the mechanisms by which these processes are regulated is rare and this lack of understanding is one of the major constraints to improved broodstock management.

Barramundi, Lates calcanfer (Bloch), also known as Asian sea bass or giant perch, is a highly valued food fish forming the basis of major fishery and aquaculture industries in Australia and south-east Asia. However, hatchery production of barramundi continues to be problematic, with unpredictable male fish performance in hatcheries. There is no published literature on the relationship between nutrition and reproduction in barramundi and brood fish are generally fed trash fish supplemented with vitamins. In order to contribute to our understanding of brood stock nutrition, particularly of male barramundi, this study has investigated the effect of three major nutritional regimes - feeding frequency (food deprivation), dietary protein:energy ratio and dietary fatty acid profile - on standard nutritional indices such as growth and body composition and on plasma steroid concentrations, GSI and histological stage of the gonads of male barramundi.

To test the effect of feeding frequency, groups of relatively small (700 ± 25 g) or relatively large (1000 ± 70 g) male barramundi were fed daily (D), every three days (3D) or every seven days (7D) for 24 weeks. A fourth group of each size was starved for 12 weeks and refed for a further 12 weeks. Starvation resulted in loss of body weight and tissue nutrients, while nutrients were regained and compensatory growth occurred during the refeeding period. Low feeding frequency (7D) resulted in reduced or no growth in fish, whilst fish fed more frequently (D or 3D) showed higher growth. These findings were also reflected in improved body composition of fish fed more frequently. In general, gonads were found to be cycling with a range of stages of development including development of gonia cells and appearance of spermatocytes and spermatids apparent in any particular population (treatment group) of fish. However, a larger proportion of testes from barramundi that were starved were immature compared with those of fish in other treatments. Feeding regime affected the hormone production in the smaller and larger fish differently. Although starvation or low nutrient intake did not influence the low Oestradio1-17β (E₂) levels in small fish, the relatively higher E2 level in larger fish was clearly reduced by starvation. In contrast, relatively high Testosterone (T) level of small fish was reduced by starvation but low T level was not influenced by starvation in large fish. In the less extreme treatments, the effects were not as clear. The large fish in D or 3D regimes increased plasma T level although not significantly and plasma E₂ level significantly decreased at week 18. A period of refeeding after starvation clearly influenced the concentration of plasma steroid hormones in both size groups.

To test the effect of protein:energy ratio, groups of male barramundi were presented with diets containing 50% protein and either 15 MJ.kg⁻¹, 18 Mike, 21 M.J.kg⁻¹ or 24 MJ.kg⁻¹ by varying dietary lipid for a 24 week period. Comparable growth was observed in all animals with low energy diets being consumed at a greater rate to compensate for the lack of energy. Body composition analysis showed that high dietary energy led to greater fat storage. As with the starved animals, gonads of fish fed the lowest energy diet were consistently found to be at an early developmental stage with tightly packed gonia cells and gonads of fish in other treatments showed evidence of normal cycling. Dietary energy level did not significantly affect the plasma hormone levels in male barramundi. Plasma E2 was relatively low throughout and did not show differences between treatments. Plasma T level reduced with time and similarly did not vary between treatments. Plasma 1 1keto Testosterone (11kT) did not show any particular trend with dietary protein:energy ratio, even in the lowest energy diet.

To test the effect of dietary fatty acid levels, groups of fish were fed with one of four diets (50 % protein, 21 M.J.kg⁻¹) containing either linseed oil (enhanced levels of 18:3 n-3), soybean oil (enhanced levels of 18:2 n-6), fish oil (enhanced levels of 20:5 n-3 and 22:6 n-3) or Aquagrow (enhanced levels of 20:4 n-6) for 18 weeks. Fish fed a diet high in short chain n-3 fatty acids derived largely from linseed oil had lower growth than those of other treatments. Fish fed short chain n-6 and long chain n-3 fatty acids had intermediate growth and fish fed long chain n-6 had the highest growth. Tissue fatty acid profiles were highly correlated with the dietary fatty acid profile, but evidence was also obtained that barramundi preferentially accumulate long chain HUFA into the gonad. No apparent effect on the stage of gonadal development as a result of dietary fatty acid profile was observed. Nor did dietary fatty acid profile affect the circulating concentration of plasma T or E₂. Plasma E₂ level was low at week 18 and plasma T level showed similar changes in all treatments. Plasma 11kT level clearly declined with time and it is suggested that this may have been in response to the high dietary fatty acid levels negatively affecting hormone production. Alternatively, high dietary fatty acid levels used in this study may have inhibited plasma T production with subsequent decreases in production of 11kT from its precursor T.

The principle conclusion from this study is that extreme cases of nutrition (starvation, refeeding, low dietary energy) impact on male barramundi reproductive development, but under less extreme conditions, there appeared to be little effect. This is in agreement with some of the data in the literature, which indicates that male fish expend less energy on reproduction and so are less affected by moderate changes in nutritional conditions. Conclusions regarding the effects of the moderate treatments are constrained since there appeared to be other circumstances impacting upon the experiments. Difficulties experienced with poor quality feeds and resulting long acclimation periods, disease events and the fact that relatively small gonad sizes observed in all experiments, even in the presence of gametogenesis indicate that the conditions may not have been ideal for reproductive development.

Thus, this study must be considered a preliminary investigation. It does nevertheless provide a significant platform for future work regarding the effects of nutrition on male barramundi broodstock development and teleost reproduction in general.

Item ID:	33768
Item Type:	Thesis (PhD)
Keywords:	aquaculture; Asian sea bass; barramundi; development; diet; feeding; giant perch; growth; Lates calcarifer; nutrition
Date Deposited:	21 Jul 2015 04:20
FoR Codes:	07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 30% 07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070204 Animal Nutrition @ 70%
SEO Codes:	83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830102 Aquaculture Fin Fish (excl. Tuna) @ 100%
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