No abstract

, corresponding to 2.8 times the RMR. When converted to its energy equivalent, total magnitude of SDA was linearly correlated with ration size to a maximum of 192·kJ·kg -1 ·h -1 , and as a proportion of gross energy ingested (SDA coefficient), it averaged 35±2.2%. These results demonstrate that, although the factorial increase of SDA in SBT is similar to that of other fish species, the absolute energetic cost of SDA is much higher. These results support the contention that tuna are energy speculators, gambling high rates of energy expenditure for potentially higher rates of energy returns. The ration that southern bluefin tuna require to equal the combined metabolic costs of SDA and RMR is estimated in this study to be 3.5%M b of Australian sardines per day.

Owing to the inherent difficulties of studying bluefin tuna, nothing is known of the cardiovascular function of free-swimming fish. Here, we surgically implanted newly designed data loggers into the visceral cavity of juvenile southern bluefin tuna (Thunnus maccoyii ) to measure changes in the heart rate ( f H ) and visceral temperature (T V ) during a two-week feeding regime in sea pens at Port Lincoln, Australia. Fish ranged in body mass from 10 to 21 kg, and water temperature remained at 18-198C. Pre-feeding f H typically ranged from 20 to 50 beats min K1. Each feeding bout (meal sizes 2-7% of tuna body mass) was characterized by increased levels of activity and f H (up to 130 beats min K1 ), and a decrease in T V from approximately 20 to 188C as cold sardines were consumed. The feeding bout was promptly followed by a rapid increase in T V , which signified the beginning of the heat increment of feeding (HIF). The time interval between meal consumption and the completion of HIF ranged from 10 to 24 hours and was strongly correlated with ration size. Although f H generally decreased after its peak during the feeding bout, it remained elevated during the digestive period and returned to routine levels on a similar, but slightly earlier, temporal scale to T V . These data imply a large contribution of f H to the increase in circulatory oxygen transport that is required for digestion. Furthermore, these data oppose the contention that maximum f H is exceptional in bluefin tuna compared with other fishes, and so it is likely that enhanced cardiac stroke volume and blood oxygen carrying capacity are the principal factors allowing superior rates of circulatory oxygen transport in tuna.

WHENthe study of the preparation of levulose (0) from the Jerusalem artichoke (Helianthus tuberosas) was undertaken at

Feed nutritional quality impacts on the performance of aquacultured species. This study was undertaken to assess the consequences of existing postharvest handling practices on nutritional quality of local baitfish (Australian sardines, Sardinops sagax and redbait, Emmelichthys nitidus nitidus) used to feed farmed southern bluefin tuna (Thunnus maccoyii). Controlled experiments were then undertaken to determine the most appropriate postharvest treatments to maintain baitfish nutritional quality, assessed through measurement of vitamins C and E, histamine, K value and TBARS. During frozen storage (−18 °C) vitamins and fish freshness decreased significantly and rancidity increased; after approximately 3 months baitfish were of questionable utility, particularly as a source of antioxidants. On‐land freezing method [i.e. block or individually quick frozen (IQF)] affected vitamin E loss with IQF sardines losing vitamin E faster than block‐frozen baitfish. Block‐frozen baitfish, particularly sardines, should be thawed in seawater, not air or freshwater, to minimize vitamin losses. Thawing time should be no more than 2 days, and baitfish storage less than 3 months. Thiobarbituric acid reactive substances (TBARS) correlated well with remaining vitamin E, indicating its usefulness as an indicator of antioxidant status. TBARS analysis is methodologically simpler, faster and cheaper than that for vitamins, and is therefore recommended for determination of baitfish nutritional quality.