Effects of commercial diets and temperature on the growth performance and stress response of hapuku (Polyprion oxygeneios)

There is a growing interest in the development of hapuku (Polyprion oxygeneios) for aquaculture in New Zealand and Australia. This is driven by the high value of this species prized for its excellent flesh quality, texture and its rapid growth capability. As a relatively new aquaculture candidate, little is currently known about their thermal tolerance and stress response. Juveniles inhabit surface waters, have a high rate of growth and move into a demersal habitat at an age between 3 and 4 years, where water temperature is cooler (7-15. °C) and more stable. The sea surface temperature in New Zealand can reach 22. °C during the summer months in more northerly locations, and captive rearing has indicated that during periods of high temperature, growth is reduced and it is possible that the physiological response is compromised. We examined the effects of two rearing temperatures (18. °C and 22. °C) and three commercial diets on the growth of P. oxygeneios during a 14 week trial. At the end of this trial, fish were exposed to a crowding stressor, and their stress response (plasma cortisol, glucose and cholesterol levels) determined. In addition, we examined the temporal stress response of P. oxygeneios acclimated to 18. °C and 22. °C subjected to a single acute handling stress. Specific growth rate and condition factor significantly increased over time in fish reared at 18. °C, but not at 22. °C. Plasma cortisol levels in hapuku prior to and after application of the stressors were within the range observed in other teleost species and the magnitude of the cortisol response was higher in hapuku subjected to crowding than handling stress. In summary, the results indicated that rearing P. oxygeneios at temperatures of 22. °C compromised their growth and that all three diets tested promoted growth in hapuku reared at 18. °C but not at 22. °C.Statement of relevanceHapuku over 1 kg had better growth rates at 18. °C than 22. °C.

Rapidly cured out-of-autoclave laminates: understanding and controlling the effect of voids on laminate fracture toughness

Voids are one of the most significant defects found within composites and have been demonstrated to reduce the performance of composite structures. The understanding of the impact of the size and distribution of voids on laminate properties is still limited because voids have proven difficult to deliberately control. This study aims to understand the mechanisms by which voids are generated within out-of-autoclave cured laminates. In this study, a process of prepreg conditioning was developed to control the level of voids within test laminates. Non-conditioned laminates highlighted signs of void growth (1.5%), while conditioned laminates showed consistently low levels of voids (<0.3%). Mass spectrometry indicated higher levels of aqueous and solvent volatiles within the non-conditioned prepreg. Finally, Mode II fracture testing revealed a 21% improvement in toughness for the non-voided laminates. A model on the effect of voids within the Mode II stress state has also been proposed.

Viability of tallow inclusion in Atlantic salmon diet, as assessed by an on-farm grow out trial

The results of a recent increase in research interest directed at the inclusion of tallow in fish feed formulations are suggesting tallow is viable as a potential substitute for other alternative lipid sources such as poultry by-product oil. Although strong growth performance data has been shown, reservations still exist regarding reduced digestibility and the potential impacts this could have on performance over the duration of a grow-out period in low temperature conditions. Also little information is yet available on the potential effect of dietary tallow inclusion on final product quality. A large scale farm based study testing the inclusion of tallow at 40% inclusion, partially replacing poultry by-product oil, in commercial diets of Atlantic salmon over a winter grow-out period in southern Tasmania, Australia was conducted. Tallow inclusion had no impact on growth performance or nutrient digestibility. Tallow resulted in a slight improvement in fillet quality exhibiting a significant reduction in n - 6 PUFA and the n6:n3 ratio, and an increased n - 3LC-PUFA tissue deposition. Consumers were unable to display any preference in liking between 3 salmon products (cold smoked, hot smoked, and cooked) as a result of tallow inclusion. This study demonstrates the viability of partial inclusion of tallow in Atlantic salmon diets over a winter grow-out period. Statement of relevance: Improved knowledge of alternative dietary energy sources (oils and fats) to be used in aquafeed, (replacing the increasingly expensive, and diminishingly available, fish oil) is a key area of research towards improved environmental sustainability and economic viability of the aquaculture sector. Following a promising laboratory based, research scale, in vivo trial aimed at assessing the viability of tallow in salmon feed, a larger and longer duration farm-based trial was implemented to validate initial findings. Consumer test of final products (fresh-cooked, hot smoked and cold smoked fillets) showed no modification of sensorial attributes. Tallow is hereto shown to be a highly viable alternative oil for the salmon aquafeed industry.