Nankervis, L., Matthews, S.J., and Appleford, P. (2000) Effect of dietary non-protein energy source on growth, nutrient retention and circulating insulin-like growth factor I and triiodothyronine levels in juvenile barramundi, Lates calcarifer. Aquaculture, 191 (4). pp. 323-335.

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Abstract

In this study, the effect of the ratio of lipid to carbohydrate non-protein energy sources on the growth and circulating insulin-like growth factor (IGF)-I and triiodothyronine (T3) levels of juvenile barramundi was examined using a 2×3 factorial design experiment. Isonitrogenous diets (50% crude protein) were formulated at two gross energy levels (18 and 21 MJ kg−1) and three ratios of lipid to carbohydrate non-protein energy (60:40, 70:30 and 80:20). Animals were held in 70 l aquaria receiving recirculated seawater (28 ‰) at 25°C. Animals were fed daily to satiety for 70 days. T3 and IGF-I levels were measured using radioimmunoassays validated for use for this species. Lipid and carbohydrate energy were supplied as marine fish oil and gelatinized corn starch, respectively. Gelatinized starch was generally well utilized by juvenile barramundi, though its utilization may be limited above the 17% inclusion level. Increases in dietary energy resulted in higher growth rates and feed conversion as well as elevated protein and lipid gain. A significant protein sparing effect of both carbohydrate and lipid was demonstrated for juvenile barramundi. Circulating levels of T3 and IGF-I responded to dietary treatment, however they did not relate directly to any measured growth parameter. The relationships between nutrition, growth and the underlying mechanisms controlling growth are discussed.

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