Abstract
Feed requirements were estimated from specific growth rates in standardized soft tissue dry weight (SGRDW’) and atomic O:N ratios for mussels fed seven rations of microalgae (5–735 μg C h−1 ind−1) at 7 and 14°C respectively. The mean oxygen consumption and ammonia-N excretion rates were significantly higher at 14°C (0.29 μg O2 and 27.3 μg N ind−1 h1) compared with those at 7°C (0.16 μg O2 and 11.4 μg N ind−1 h−1) (P < 0.05), resulting in O:N ratios between 3 and 45 at 7°C and 7 and 28 at 14°C. Low O:N ratios indicate protein catabolism and an unfavourable condition, whereas high ratios indicate that carbohydrate is the primary energy source. The measured SGRDW’ suggests minimum feed requirements of ~240 and ~570 μg C ind−1 h−1 for weight maintenance at 7 and 14°C, with corresponding O:N ratios of 24 and 16, respectively, indicating a more stressed condition at 14°C. A 0.5% SGRDW’ day−1 was obtained by ~565 (O:N = 29) and ~680 (O:N = 23) μg C ind−1 h−1 at 7 and 14°C respectively. A positive and significantly higher SGRDW’, with the lowest feed ration at 7°C compared with a negative SGRDW’ at 14°C (P < 0.05), indicated that storage time can also possibly be prolonged at low temperatures if the mussels are not fed.