Effect of dietary vitamin A in live feeds on performance and skeletal malformations of striped trumpeter Latris lineata larvae and post-larvae

Reducing malformation is a constant challenge in the aquaculture production of marine finfish throughout the world. Several nutritional studies have previously linked vitamin A (VA) to abnormalities in skeletogenesis during marine fish larval development. Striped Trumpeter, Latris lineata, is a marine fish native to south-eastern Australia and New Zealand that has been successfully cultured at a semi-commercial scale in the hatchery and sea cages. My project aim was to examine if dietary VA during the live feed period affects larval performance and skeletal development, especially the jaws and vertebral column, and determine the nutritional VA requirement. The first part of the project was to accurately measure and quantify VA in live feeds and fish larvae using two extraction methods. The first method measured total VA in terms of retinyl palmitate, retinol and retinoic acid and the second method measured total retinol. The second part of the project was to determine the optimal conditions to enrich rotifers and Artemia with VA (retinyl palmitate) through examining the effects of time and light. This was followed by examining the effect of water type (clear and greenwater) on VA content of enriched rotifers over time. The optimal enrichment time for VA enrichment was 2 h for rotifers in dark conditions and 12 to 24 h for Artemia. The enrichment of rotifers and Artemia with VA was not uniform, and rotifers displayed a higher retinoid inclusion pattern than Artemia. Water type, time spent in larval rearing water after enrichment and the previous VA enrichment levels affected the concentration of retinoids in the VA-enriched rotifers. In clearwater, the concentration of retinoids in VA-enriched rotifers decreased over time, while in greenwater, the retinoid concentration decreased in the high VA-enriched rotifers and increased in the low VA-enriched rotifers. The significant difference in VA content of prey from graded VA enrichments was maintained for at least 4 h in clearwater and 4 to 8 h in greenwater. The third part of the project was to feed L. lineata larvae with VA-enriched rotifers or Artemia using dose-response experimental designs. The first experiment tested the effect of feeding VA-enriched 2 rotifers (eight doses of VA, 0.5 to 92.5 ng retinol mg\(^{-1}\) DW rotifers) to L. lineata larvae in 24 replicate 300 l tanks and reared in greenwater from 6 to 18 days post hatch (dph), followed by a four week period on Artemia (from 17 to 43 dph) to allow post-larvae to fully develop the jaw and skeletal elements. The second experiment investigated the potential impact of retinoids derived from microalgae by testing the combined effect of green or clearwater and enriched rotifers (three doses of VA, 0.6 to 99.6 ng retinol mg\(^{-1}\) DW rotifers). The last experiment tested the effect of feeding enriched Artemia (six doses of VA, 0.4 to 44.1 ng retinol mg\(^{-1}\) DW Artemia) for four weeks (from 17 to 44 dph). The results showed that VA incorporation into L. lineata larvae varied with different doses of VA in the enriched rotifers and Artemia, while the water type did not affect the VA content in the larvae. The performance of L. lineata larvae and post-larvae was not affected by dietary VA during either the rotifer or Artemia feeding periods, while greenwater affected growth (9.2% and 28.0% increase in length and weight, respectively, over clearwater, by 43 dph). Dietary VA did not affect the onset or types of jaw malformations in post-larvae during the rotifer or Artemia feeding period experiments (81 and 50% prevalence of commercially relevant malformations on 43 and 44 dph, respectively). However, jaw malformation severity was reduced when larvae were reared in greenwater (2%) compared with those reared in clearwater (14%). Dietary VA during the rotifer feeding period affected the prevalence of vertebral column malformations which were correlated with the larval VA content, where daily inclusion of ≤ 123 ng total VA mg\(^{-1}\) DW rotifer, equivalent to ≤ 35ng total retinolmg\(^{-1}\) DW rotifer, can reduce the skeletal malformations to approximately 30%. To my knowledge, this research is the first to examine the effects of increasing doses of VA through enrichment of live feeds, during two different larval developmental stages, on the performance and skeletal development of the same marine fish. Also, it is the second study to explore the effect of graded VA doses in enriched rotifers through dose-response experimental design on skeletal malformations in a marine finfish. The overall conclusion was that dietary VA has no effect on the growth or survival of L. lineata larvae and also has little or no effect on the jaw malformation in L. lineata larvae, where physical factors, including the size of rearing tanks, tank colour, and water type, have a greater, and potentially masking, effect on jaw malformation. However, dietary VA was found to significantly affect vertebral column malformations only during the rotifer feeding period. The study highlights the species-specific nature of the effect of VA on malformations, and that marine larvae are more sensitive to the VA treatment when they are younger, during the formative stage of skeletal development