Feeding and on-growing strategies for yellowtrail flounder Limanada ferruginea (Storer)

"Give a person a fish and he will have food for a day; teach him to grow fish and he will have food for a lifetime", so goes the old Chinese saying. Application of this wisdom on a world-wide scale could go a long way in producing food for the hungry millions. To help spread this principle and philosophy is important in aquaculture. This thesis focuses on strategies to improve the growing techniques of juvenile flatfish with emphasis on yellowtail flounder, Limanda ferruginea (Storer), which has been identified as a potential species for cold-water aquaculture along the north-east coast of Canada. -- Optimal food rations can affect the commercial success of any aquaculture venture. The effects of ration levels on growth performance of 0+ juvenile yellowtail flounder was examined for fish held under a 16L:8D photoperiod. Two experiments were conducted; the first using ration levels of 1, 2, 4, 6% (body weight⋅d⁻¹ (bw ⋅d⁻¹)) on small juveniles (mean initial weight ± SE 1.0 ± 0.04 g) held at 7.0°C with a stocking density of 0.95 kg⋅m⁻ ²(~ 45% bottom coverage). The second experiment used ration levels of 1, 1.5, 2, 3% bw ⋅d⁻¹ on large juveniles (mean initial weight ± SE 7.39 ± .07 g) held at 10°C with a stocking density of 1.45 kg⋅m⁻² (~ 34% bottom coverage). Survival in both experiments was not significantly different. Results of experiment 1 indicated that fish fed 1% bw ⋅d⁻¹ had significantly lower growth (weight, length, body depth and specific growth rates)(p<0.05) than those fed 2, 4 and 6% bw ⋅d⁻¹. Significant differences (p<0.05) with gross food conversion rations (GFCR's) were found between fish fed rations of 1% and 2% and those fed 4% and 6% rations, but 4-6% bw ⋅d⁻¹ were poor in terms of gross food conversion ratios, resulting in food wastage. Results of experiment 2 indicated that fish fed 1, 1.5 and 2% bw ⋅d⁻¹ had significantly lower growth (weight, length and specific growth rates) (p<0.05)than fish fed 3% bw ⋅d⁻¹. Gross food conversion rations (GFCR's) were significantly different (p<0.05) for all 4 rations. Overall, this study demonstrated that it would be more feasible to use a ration of 2% bw ⋅d⁻¹ for small juveniles and 1-1.5% bw ⋅d⁻¹ for large juveniles. -- It has been demonstrated that increased photoperiods improve growth and survival during the larval stage of this species. I conducted an experiment to determine the effect of photoperiod on growth and survival of 1+ juvenile yellowtail flounder. This experiment compared growth and survival rates of juveniles (mean initial weight ± SE = 9.25 ± 0.22 g) under 24, 18, 12 and daily ambient photoperiod. A stocking density of 0.47 kg⋅m⁻² (~10% bottom coverage) and a feeding ration of 2% (body weight⋅d⁻¹ (bw⋅d⁻¹)) was used. Temperature was held at 7.0°C. No significant differences in growth or survival among juveniles were found under the different photoperiods. It appears that the most cost-effective approach is to provide a simulated natural photoperiod for juvenile yellowtail flounder. -- There is a need for an "optimal stocking density" of juvenile flatfish to be established for cultured species in hatchery situations. This final study in my thesis examined the effects of three different stocking densities on the growth performance and survival of 0+ juvenile yellowtail flounder held under 16L:8D photoperiod. Three densities of 0.47,0.95 and 1.9 kg⋅m⁻² with 23%, 45% and 90% bottom coverage was used. Juvenile yellowtail (mean initial weight ± SE = 1.02 ±0.05 g) were fed a feed ration of 2% (body weight⋅d⁻¹ (bw⋅d⁻¹)). Temperature was 7.0°C. No significant differences in growth or survival between juveniles were found under the different stocking densities. However, stocking densities with 90% bottom coverage had slightly lower growth rates and higher gross food conversion ratios. -- Overall results suggests that juvenile yellowtail flounder can be stocked at densities greater than 100% bottom coverage. Economically, it appears more feasible to use a ration of 2% bw⋅d⁻¹ for small juveniles and 1-1.5% bw⋅d⁻¹ for larger juveniles and it appears that the most cost-effective approach is to provide simulated natural photoperiod (min. 6-8 hours) for juvenile yellowtail flounder production.

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