Effects of wild and farm-grown macroalgae on the growth of juvenile South African abalone Haliotis midae Linnaeus
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The effect of various macroalgal diets on the growth of grow-out (> 20 mm shell length) South African abalone Haliotis midae was investigated on a commercial abalone farm. The experiment consisted of four treatments: fresh kelp blades (Ecklonia maxima [Osbeck] Papenfuss) (~ 10 % protein); farmed, protein-enriched Ulva lactuca Linnaeus (~26 % protein) grown in aquaculture effluent; wild U. lactuca (~ 20 % protein); and a combination (mixed) diet of kelp blades + farmed U. lactuca. Abalone grew best on the combination diet (0.423 ± 0.02% weight dayˉ¹ SGR [specific growth rate]; 59.593 ± 0.02 µm dayˉ¹ DISL [daily increment in shell length]; 1.093 final CF [condition factor]) followed by the kelp only diet (0.367 ± 0.02 % weight dayˉ¹ SGR; 53.148 ± 0.02 µm dayˉ¹ DISL; 1.047 final CF), then the farmed, protein-enriched U. lactuca only diet (0.290 ± 0.02% weight dayˉ¹ SGR; 42.988 ± 0.03 µm dayˉ¹ DISL; 1.013 final CF) that in turn outperformed the wild U. lactuca only diet (-0.079 ± 0.01 % weight dayˉ¹ SGR; 3.745 ± 0.02 µm dayˉ¹ DISL; 0.812 final CF). The results suggest that protein alone could not have accounted for the differences produced by the varieties of U. lactuca and that the gross energy content is probably important.