The effect of feed frequency on growth, survival and behaviour of juvenile spiny lobster (Panulirus ornatus)

Spiny lobsters have a range of complex chemical communication pathways that contribute to feeding behaviour. Feed intake is modulated by feed availability and feed characteristics, such as attractiveness and palatability, with behavioural factors, such as social competition and circadian rhythm, providing an extra layer of complexity. In this study, we investigated the effect of feed frequency on survival and growth of early-stage (instar 26) juvenile Palunirus ornatus. In addition, we investigated the interactive effect of feed frequency and circadian rhythm on lobster feed response. Lobsters were fed a set ration at a frequency of either one, two, four, eight, sixteen or thirty-two times per day over 49 days. The effect of feed frequency on growth and survival was determined. Circadian feeding activity under these feeding treatments was assessed by time-lapse photography. Increased feed frequency from one to sixteen feeds daily improved growth by increasing apparent feed intake (AFI) and feed attraction, as confirmed by the increased presence of lobsters in the feeding area. The rapid leaching of feed attractant, particularly free amino acid, suggests a beneficial effect of multiple feeding frequencies on feed intake and growth. However, more than sixteen feeds per day resulted in decreased feed intake and a subsequent reduction in growth. The decrease in feed intake is thought to be associated with saturation of the culture environment with attractants, resulting in a reduced behavioural response to feed supplies. This may indicate the need for depletion of attractants to retrigger a feeding response. As lobsters were grown communally, faster growth at sixteen rations per day was also coupled with increased cannibalism, likely driven by increased vulnerability with the occurrence of more frequent ecdysis events. Whereas circadian rhythm indicated more activity at night, an interaction between daytime activity and feed frequency was not observed

The interactive effect of dietary choline and water temperature on the liver lipid composition, histology, and plasma biochemistry of juvenile yellowtail kingfish (Seriola lalandi)

The study examined the interactive effects of choline content (supplied as choline chloride salt (CC); no added CC, 3.0, or 6.0 g CC kg−1 diet) and water temperature (16 °C vs 24 °C) on liver lipid composition, liver histology and plasma biochemistry. Liver and plasma samples were collected from juvenile yellowtail kingfish (Seriola lalandi; YTK; 156 g body weight), fed fishmeal-based practical diets, at the conclusion of an eight-week feeding experiment. The results showed that higher liver lipid content at 24 °C was due to greater triacylglycerol (TAG) accumulation. Liver phospholipids content remained similar regardless of CC supplementation and temperature (P > 0.05). As expected, liver phospholipids were mainly composed of phosphatidylcholine (PC); however, in most cases liver phospholipids were almost completely made up of PC. Phospholipid classes were also not significantly affected by CC supplementation and temperature. The results indicate that these lipid classes were tightly regulated in the liver of juvenile YTK. Fatty acids composition among TAG, FFA, and phospholipids fractions were different; however, within the phospholipids fraction, the long chain polyunsaturated fatty acids (LC-PUFA) proportion in the liver of YTK remained unchanged regardless of treatments. In general, histological examination did not show severe lesions in fish livers across all treatments. Fish also had significantly more hepatocytes with large nuclei at 16 °C than at 24 °C which is a response that requires further research. Plasma analytes were profoundly affected by temperature rather than by CC supplementation; however, there is no strong evidence indicating compromised health in fish reared at either temperature. This study demonstrates that fish fed fishmeal-based practical diets generally had normal looking livers; nevertheless, some liver and plasma health indicators can be affected in juvenile YTK reared at sub-optimal temperatures and fed diets without supplemented choline

Effect of dietary lipid source on expression of lipid metabolism genes and tissue lipid profile in juvenile spiny lobster Sagmariasus verreauxi

The spiny lobster Sagmariasus verreauxi is an emerging lobster species for intensive aquaculture. The lack of any nutritional information required for feed development in this species initiated this study to understand the effect of different dietary lipid sources on tissue lipid profiles and expression of selected lipid metabolising genes. Krill oil, marine oil (blend of fish oils), and vegetable oil (combination of linseed and palm oil), were utilised to formulate three experimental feeds with different phospholipid, triacylglycerol and polyunsaturated fatty acid profiles. Experimental feeds were administered to freshly moulted juvenile S. verreauxi for 50 to 55 days, to determine the effect of lipid sources on the nutritional status, fatty acid composition and expression of genes related to fatty acid biosynthesis, β-oxidation, lipid catabolism and regulation of lipid metabolism. While there were no significant differences in terms of weight gain and mortality among different dietary treatments, the fatty acids composition in the hepatopancreas and to some extent, muscle tissues correlated with the fatty acids composition of the respective dietary treatments. Vegetable oil diet resulted in higher expression of genes related to β-oxidation, which indicates selectivity towards utilisation of monounsaturated fatty acids for energy in this species. In tandem, genes related to fatty acid and cholesterol biosynthesis were upregulated, suggesting their importance in the marine lobster diet. This is the first report on the use of formulated feeds to successfully maintain juvenile S. verreauxi

n-3 LC-PUFA deposition efficiency and appetite regulating hormones are modulated by the dietary lipid source during rainbow trout grow-out and finishing periods

Largely attributable to concerns surrounding sustainability, the utilisation of omega-3 long-chain polyunsaturated fatty acid-rich (n-3 LC-PUFA) fish oils in aquafeeds for farmed fish species is an increasingly concerning issue. Therefore, strategies to maximise the deposition efficiency of these key health beneficial fatty acids are being investigated. The present study examined the effects of four vegetable-based dietary lipid sources (linseed, olive, palm and sunflower oil) on the deposition efficiency of n-3 LC-PUFA and the circulating blood plasma concentrations of the appetite-regulating hormones, leptin and ghrelin, during the grow-out and finishing phases in rainbow trout culture. Minimal detrimental effects were noted in fish performance; however, major modifications were apparent in tissue fatty acid compositions, which generally reflected that of the diet. These modifications diminished somewhat following the fish oil finishing phase, but longer-lasting effects remained evident. The fatty acid composition of the alternative oils was demonstrated to have a modulatory effect on the deposition efficiency of n-3 LC-PUFA and on the key endocrine hormones involved in appetite regulation, growth and feed intake during both the grow-out and finishing phases. In particular, n-6 PUFA (sunflower oil diet) appeared to ‘spare’ the catabolism of n-3 LC-PUFA and, as such, resulted in the highest retention of these fatty acids, ultimately highlighting new nutritional approaches to maximise the maintenance of the qualitative benefits of fish oils when they are used in feeds for aquaculture species