not corrected for dominance and epistatic interaction effects) 13 of swimming performance were estimated by Garenc et al.
Genetic parameter estimates for swimming performance in fish are scarce, but suggest that swimming performance has a heritable component. The heredity of athletic performance has received considerable research attention in dog 9, horse 10, 11 and human 12. Hence, U crit could be a good indicator of oxygen uptake efficiency of individual tilapia. Particularly for tilapia, the link between U crit and maximal oxygen consumption may be strong because tilapia has a high U crit (4.94 ± 0.45 BL s −1 for ~ 15 cm fish) and a very high maximum metabolic rate 8. Fish that are able to consume more oxygen can swim faster, or reverse for the connection that we are interested in: faster swimming fish have higher oxygen uptake efficiency. Near U crit, the metabolic demand for oxygen is becoming greater than can be provided by ventilatory and circulatory systems 7. Oxygen uptake is maximal at U crit, although the anaerobic component by fast skeletal muscle increases when nearing U crit 6. Recently we have developed and applied such tests for gilthead seabream ( Sparus aurata) and Atlantic salmon ( Salmo salar) 5. Individual fish fatigue when swimming at a specific speed interval for a certain period, from which the U crit 3 can be determined. In this test, swimming speeds are incrementally increased at prescribed intervals until fish stop swimming and fatigue 3, 4. As critical swimming speed ( U crit) may reflect the oxygen uptake efficiency, the hypothesis is that fish with high U crit will grow better under conditions where oxygen is limiting.Ī high throughput method to assess the individual variation in oxygen uptake efficiency is by subjecting fish to exhaustive exercise in a critical swimming challenge test. It may be expected, therefore, that Nile tilapia with high oxygen uptake efficiency may grow better under these conditions than Nile tilapia with low oxygen uptake efficiency. Low DO in smallholder farms negatively affects Nile tilapia growth 2. In non-aerated ponds, dissolved oxygen (DO) drops below critical level (3 mg l −1 1) during the night. Nile tilapia ( Oreochromis niloticus) is predominantly produced in smallholder tilapia ponds without aeration. We conclude that U crit in Nile tilapia is heritable and can be used to predict growth performance. These results suggest a juvenile trade-off between swimming and growth performance where fish with high U crit early in life show slower growth later under conditions of limited oxygen availability. The estimated r g between absolute U crit and HW, and absolute U crit and DGC were − 0.21 and − 0.63 respectively, indicating that fish with higher absolute U crit had lower growth in the non-aerated pond as compared to fish with lower absolute U crit. The estimated r g between absolute U crit and fish size at testing were all strong and positive (range 0.72–0.83). Substantial heritability was found for absolute U crit (0.48). Our objectives were to estimate variance components for U crit and fish size at swim testing early in life, and genetic correlations ( r g) between U crit with harvest weight (HW) and daily growth coefficient (DGC) later after grow-out in a non-aerated pond. Critical swimming speed ( U crit, in cm s −1) is a potential indicator for O 2UE. We hypothesize that Nile tilapia with high oxygen uptake efficiency (O 2UE) may perform better under these conditions than Nile tilapia with low O 2UE. Nile tilapia is predominantly produced in smallholder ponds without aeration.
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