Elevated temperature promotes growth and feed efficiency of farmed ballan wrasse juveniles (Labrus bergylta)

Abstract

The expansion of ballan wrasse farming, used as a biological control against sea lice in Atlantic salmon, is constrained by the slow growth rate in the species and extended period required to reach deployment size. Rearing temperature and diets are the two main growth limiting factors in fish. In this study, farmed ballan wrasse juveniles were reared at 10, 13 and 16 ºC over a period of 3 months and fed two different commercial diets commonly used in marine finfish, Otohime S2 and BioMar Symbio. At the end of the trial, fish growth was +125, +75 and +25 % compared to their initial weight in 16, 13 and 10 ºC treatments, respectively. It was suggested that temperatures above 16 ºC may promote growth even further. Furthermore, feed conversion ratio was significantly improved in fish reared at 16 °C. However, diets did not impact on any of the growth performance indicators although a significantly higher daily feed intake was observed in fish fed BioMar Symbio. Importantly, no significant effects of temperature and diets on mortality and condition factor were observed. No differences were found in the fish (whole-body) macronutrient composition between diets. Analysis of the protein, lipid and energy digestibility revealed lower apparent digestibility coefficients than normally observed in marine species, suggesting the diet formulation is not optimised for the species. Finally, fish reared at 10 ºC showed increased hepatosomatic index, suggesting fat storage in the liver under cold temperatures. These results showed that the production cycle could be shortened by more than 4 months in fish reared at 16 ºC. This could contribute to increase hatchery productivity and meet demand from the salmon production sector while reducing costs associated with the nursery phase although maintaining a constant high temperature would increase operational costs.

Sea temperature effects on depth use and habitat selection in a marine fish community

“…Ballan wrasse used the warmest water layers available throughout the year. This warm-water affinity was not unexpected, given its southern distribution range and relatively high optimal temperature for growth (>16°C; Cavrois-Rogacki et al, 2019;Yuen et al, 2019).…”

“…Finally, ballan wrasse is the most warm-water-adapted species, occurring from Morocco up to southern Norway (Sayer & Treasurer, 1996). Juveniles (~15 g) grow faster at temperatures above 16°C (Cavrois-Rogacki et al, 2019), whereas larger individuals (~300 g) also show increased physiological performance when temperature increases from 0 to 25°C, with low metabolic rates and inactivity at low temperatures, that is, 5-10°C (Yuen et al, 2019). In coastal Skagerrak, cod typically avoids shallow waters when temperatures rises above 16°C and instead choose deeper waters that are up to 5°C cooler (Freitas et al, 2015(Freitas et al, , 2016.…”

Cleaner fish behavioral ecology: Its implications toward wild fishery and salmonid aquaculture sustainability

“…Their low metabolic rates and inactivity at 5-10℃ suggests that their efficiency as cleaner fish will be limited in winter and in higher latitude locations [21]. While elevated temperature promotes growth and feed efficiency as observed in farmed ballan wrasse juveniles [22]. The clear evidence of lumpfish grazing efficacy on sea lice was also reported by Imsland et al, [23], through gastric lavage which was performed every 2 weeks for 54 days farmed in low temperature (9-12℃).…”

Developmental stages of the ballan wrasse from first feeding through metamorphosis: Cranial ossification and the digestive system

“…There were low levels of fat deposit in the hepatocytes. Liver size and fat deposition have been observed to be temperature dependent (Cavrois‐Rogacki et al, 2019 ). The liver size may increase as a result of hypertrophy and hyperplasia, as seen in Atlantic cod larvae (Wold, 2007 ).…”