The respiratory physiology, condition and feed intake of yellowtail kingfish (Seriola lalandi) family lines with different size-at-age

Abstract

Growth is one of the most economically valuable traits in an aquaculture breeding program. It is crucial that any artificial selection does not negatively impact the functional integrity and therefore welfare of the animal. Understanding the physiological mechanisms that underlie the diversity of certain traits may contribute to the success of a long term breeding program. The yellowtail kingfish (Seriola lalandi) as a farmed fish in New Zealand is increasing in importance. The objectives of this research was to establish whether any differences in respiratory physiology, hypoxia tolerance, feed intake and condition of S. lalandi are functionally linked with the growth performance (size-at-age) of different family lines, and whether there are any negative impacts. Experiments were conducted at the NIWA Bream Bay aquaculture park, Ruakaka. Five tanks containing five family lines underwent routine culture at 20°C ± 1°C. Prior to experimentation a PIT-tag was inserted into individual fish for identification. The large sizeat- age family (LSAF), the small size-at-age family (SSAF), and two intermediate size-at-age were subject to extensive screening protocols. A Brett-style swim flume respirometer was used to examine various aspects of respiratory performance that define the capacity of fish for growth through measures of aerobic metabolic scope. Hypoxia tolerance was investigated using in-tank “closed” respirometry techniques to assess family performance in challenging environmental conditions. Ingestion of feed containing ceramic ballotini beads followed by an X-ray of the alimentary canal allowed for assessment family-related differences in daily feed intake. All fish had their heart and body conditions examined, this included: regular assessment of weight and length, as well as measurements of the heart, liver, spleen and gonads once terminated. The heart was fixed for further assessment of ventricle dimensions. The growth of the five families did increase over time and there was a consistent difference where the LSAF was larger than the SSAF. The larger families did not always have a better FCR. There was no difference between SMR, AMR, AMS, Ucrit, Uopt and GCOT when using ANOVA between all four families, however, further examination of just the LSAF and the SSAF revealed that LSAF had a larger AMS, Ucrit and Uopt. Hypoxia displayed no significant differences in MO2 and therefore a LOS could not be resolved. However, analysis of the video footage revealed that swimming speed increased, with decreasing DO thereby masking the MO2 values. The LSAF was the faster growing and larger family which could be explained by the larger AMS whereby the greater the capacity the greater potential for growth. Hypoxia tolerance was consistent amongst families, when mass was accounted for, along with behavioural changes and there was very little difference in terms of the terminal samples. At this stage from the data collected there appears to be no negative effects on the functional integrity of S. lalandi, however, further research should be applied to individuals past the first generation in order to see if there is any alteration to the parameters, tested in this thesis, with each generation as a result of selectively breeding for optimal growth.