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Improving the feed conversion ratio (FCR; the amount of feed consumed relative to the amount of weight gain) can reduce both production costs and environmental impacts of farmed fish. The aim of this study was to investigate what drives FCR to understand how nutrients are retained, as well as the amount of oxygen consumed for digestion, absorption and assimilation (a metabolic process known as specific dynamic action, SDA). Feed-efficient and inefficient Chinook salmon (Oncorhynchus tshawytscha) in fresh water were identified using ballotini beads and X-radiography that tracked individual feed intake across three assessment periods under satiated feeding. This allowed a comparison of physiological traits and body composition between the two FCR phenotypes over two time points as Chinook salmon grew from 305 to 620 g. Fish with higher daily feed intake (DFI) had higher daily weight gain (DWG) as expected. Nonetheless, the relationship between FCR and DFI as well as FCR and DWG was variable between time points. FCR and DWG were not correlated at the first time point and were negatively correlated at the second time point. In contrast, FCR and DFI were positively correlated at the first time point but not the second. Despite this, efficient fish ate smaller meals and retained more protein, lipid and energy in their body tissues. There was no detectable difference in metabolism between the two FCR phenotypes with respect to minimal resting metabolic rate, maximum metabolic rate, aerobic scope, or SDA parameters. In conclusion, FCR is not consistently associated with growth and metabolic differences in freshwater Chinook salmon, but FCR-efficient fish retain more nutrients and consume smaller meals., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail-beat frequency, stride length, caudal fin-beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A0 ) was significantly increased in SN-disrupted fish compared with sham-operated controls. In addition, the orientation of caudal fin-tip relative to the overall swimming direction of SN-disrupted fish was significantly deflected (two-fold) in comparison with sham-operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body-wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN-disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (LF ) s(-1) . In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion., (© 2014 The Fisheries Society of the British Isles.)

There was no evidence that shelter conveyed a metabolic advantage to the false clown anemonefish Amphiprion ocellaris in terms of standard and routine rates of oxygen uptake. The metabolic and fitness benefit of shelter might not, therefore, be widespread among all fish species., (© 2013 The Authors. Journal of Fish Biology © 2013 The Fisheries Society of the British Isles.)