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A 5 week experiment was carried out with juvenile yellowtail kingfish Seriola lalandi to investigate the interactive effects of water temperature (21, 24, or 27°C) and dissolved oxygen regime (normoxic vs. hypoxic) on the growth rate, feed intake and digestive enzyme activity of this species. Specific growth rate (SGR) was highest at 24°C, regardless of oxygen regime, but the SGRs of the fish exposed to hypoxia at 21, 24 and 27°C were 13%, 20% and 17% lower, respectively, than the SGRs recorded for the fish reared under normoxic conditions. The digestive enzyme activities (i.e. trypsin, lipase and a-amylase) were influenced by temperature but did not appear to be affected by dissolved oxygen concentration. Information about the effects of water temperature and dissolved oxygen on feeding, growth and digestive capacity of juvenile yellowtail kingfish could contribute to improving feed management decisions for production of this fish species under different environmental conditions.

Praziquantel (PZQ) is registered for oral use against Benedenia seriolae infecting Seriola spp. in Japan, but its bitter taste causes poor palatability. Incorporating PZQ in a moist pellet may help mask the flavor to improve intake. Altering delivery, however, may influence efficacy. We assessed the minimum effective concentrations of PZQ in moist pellets delivered by intubation for the monogeneans Zeuxapta seriolae and B. seriolae infecting yellowtail kingfish Seriola lalandi in flow-through tanks. The optimised dose was then evaluated in a sea-cage of S. lalandi to assess feed acceptance and efficacy. During intubation trials, efficacy was assessed as a percent reduction compared to control groups; in the field trial, efficacy was assessed by a percent reduction after treatment. PZQ delivered by intubation at 70 mg kg −1 body weight (BW) for 3 d was 99.7 and 81.7% effective against Z. seriolae and B. seriolae, respectively. Increasing the dose to 120 mg kg −1 BW for 3 d had a similar efficacy against Z. seriolae (98.4%) and increased efficacy against B. seriolae to 89.2%, but partial emesis of the medicated feed was sometimes noted. S. lalandi in a sea-cage at 17°C readily consumed PZQ administered daily in moist pellets at 70 mg kg −1 BW for 3 d (inclusion rate: 5.15 g kg −1), which significantly reduced Z. seriolae and B. seriolae abundance with 99.4 and 81.6% efficacy, respectively. Juvenile B. seriolae were common on the eyes of fish post-treatment which indicates a strategically timed repeat treatment is necessary.

Ranched southern bluefin tuna Thunnus maccoyii were fed baitfishes supplemented with vitamins (predominantly E and C) or vitamins and immunostimulants, nucleotides and β-glucans, over 12 weeks after transfer and monitored for enhancement in immune response, health and performance through their 19 week grow-out period. Fish from two different tows were sampled separately at three different sampling points: at transfer to grow-out pontoons, at 8 weeks post-transfer and at harvest, 19 weeks post-transfer. Lysozyme activity was enhanced during vitamin supplementation compared to control fish. Performance (i.e. survival, condition index and crude fat), health (i.e. blood plasma variables including pH, osmolality, cortisol, lactate and glucose) and alternative complement activity were not commonly improved through diet supplementation. There were some tow-specific improvements in performance through vitamin supplementation including survival, selected parasite prevalence and intensity, and alternative complement activity. Immunostimulant supplementation also showed a tow-specific improvement in plasma cortisol level. Tow-specific responses may suggest that life history, previous health condition and husbandry can affect the success of vitamin and immunostimulant enhancement of immune response, health and performance of ranched T. maccoyii.

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