Introduction
Lumpfish and wrasse are currently used as cleaner fish as part of the overall strategy for the prevention and control of lice in Atlantic salmon farming in Norway (Skiftesvik et al., 2013; Imsland et al., 2018). There is a growing concern and criticism about the welfare and survival of cleaner fish in net pens (Treasurer and Feledi, 2014; Imsland et al., 2020; Garcia de Leaniz et al., 2021). However, there is still a lack of studies that have monitored welfare status at several localities over a long period of time. Although operational welfare indicators (OWI) that are used to evaluate welfare in net pens are widely used, there is not yet a standardized overall welfare score that would allow for comparison of welfare data of all cleaner fish species and by different studies.
It is still unclear what factors affect lumpfish and wrasse welfare most negatively. Diseases are often pointed out as the main challenge, but other factors such as suboptimal environmental conditions can also negatively affect welfare. In addition, it is still poorly documented whether production conditions also have an effect on the welfare of cleaner fish. The lice grazing efficiency of cleaner fish is known to be affected by a combination of environmental conditions and biological factors. However, it is not known whether welfare affects lice grazing efficiency.
Material and methods
Lumpfish and wrasse welfare was monitored in 2019-2022, every month, when it was possible. Individuals were weighed with a precision of 1 g. Stomach contents were visually examined and all sea lice were counted. Each OWI was scored from 0 to 3 according to Noble et al. (2019), and thereafter squared to highlight the differences between individuals with several minor injuries and individuals with much more severe wounds. The overall welfare score was then calculated as a standardized weighed sum and categorized in four degrees of severity from good to severely reduced welfare. Timing of mechanical delousing, net change and net cleaning were registered. Seawater temperature and oxygen concentration were continuously registered by each of the sea farms.
Results
Based on our welfare model, results indicate that the welfare of lumpfish progressed negatively after transfer to net pens. While newly transferred lumpfish had good welfare, a large proportion of lumpfish had clearly reduced welfare after 6-7 months at sea. The negative development related to a combination of various factors, with mechanical delousing being the most important. Our results further indicated that reduced welfare negatively impacted cleaning efficacy. Preliminary results suggest that welfare of wrasse was already compromised by the time of transfer to sea, most likely due to challenges in nurseries. Even though welfare generally appeared to improve after transfer to sea, nutritional status seemed to worsen, indicating that feeding regimes of the sea farms were not sufficiently adapted. In addition, handling (delousing and disease treatments) seemed to have a negative impact on welfare of wrasse in net pens.
Discussion
We propose a model for calculating overall welfare from OWI that ensures a systematic and comparable collection of data on large scale monitoring studies. Assessments should not be based on average values for the entire population because it can hide variations between individuals who have very different welfare statuses (Sommerset et al., 2021). Therefore, we propose to estimate an overall welfare score calculated as a weighted sum of OWI scores. This allows to highlight the differences between individuals who have a few scratches that do not greatly reduce welfare and individuals who have much more severe wounds
In accordance with other studies, we suggest that lumpfish should not be use in nets pens in summer, when the seawater temperatures are highest and delousing likely (Sommerset et al., 2021; Hvas et al., 2018). There is a clear need of improving nurseries production strategies to ensure a good welfare of wrasse by the time of transfer to sea. Improving feeding regimes for wrasse in nets pens also are a priority for welfare (Skiftesvik et al., 2017). Control over cleaner fish welfare and lice grazing efficiency in net pens can be achieved by introducing routine monitoring. This will make it possible to identify reduced welfare early, and thus implement preventive measures. Proper and sufficient allocation of resources is necessary to ensure good monitoring and therefore good welfare of cleaner fish in net pens.
References
Garcia de Leaniz, C., et al., 2021. Addressing the welfare needs of farmed lumpfish: knowledge gaps, challenges and solutions. Rev. Aquac. 14, 139-155.
Hvas, M., Folkedal, O., Imsland, A., Oppedal, F., 2018. Metabolic rates, swimming capabilities, thermal niche and stress response of the lumpfish, Cyclopterus lumpus. Biology Open 7, 1–9. doi:10.1242/bio.036079.
Imsland, A.K.D., et al. 2018. The effect of continuous light and compressed photoperiods on growth and maturation in lumpfish Cyclopterus lumpus. Aquaculture 485, 166–172.
Imsland, A.K.D., Reynolds, et al., 2020. Improving survival and health of lumpfish (Cyclopterus lumpus L.) by the use of feed blocks and operational welfare indicators (OWIs) in commercial Atlantic salmon cages. Aquaculture 527, 735476.
Noble, C., Iversen, M.H., Lein, I., Kolarevic, J., Johansen, L.H., Berge, G.M., Burgerhout, E., Puvanendran, V., Mortensen, A., Stene, A., Espmark, M., 2019. RENSVEL An Introduction to Operational and Laboratory-based Welfare Indicators for Lumpfish (Cyclopterus lumpus L.).pdf. Technical Report. FHF.
Skiftesvik, A., Bjelland, R., Durif, C., Halvorsen, K., Shema, S., Fields, D., Browman, H., 2017. Sluttrapport: Program rensefisk: Kunstig lys og rensefisk.
Skiftesvik, A.B., Bjelland, R.M., Durif, C.M., Johansen, I.S., Browman, H.I., 2013. Delousing of atlantic salmon (Salmo salar) by cultured vs. wild ballan wrasse (Labrus bergylta). Aquaculture 402, 113–118.
Sommerset, I., Jensen, B.B., Bornø, B., Haukaas, A., Brun, E., 2021. Fiskehelserapporten 2020. Technical Report 41a/2021. Veterinærinstituttet. URL: www.vetinst.no.
Treasurer, J.W., Feledi, T., 2014. The Physical Condition and Welfare of Five Species of Wild-caught Wrasse Stocked under Aquaculture Conditions and when Stocked in Atlantic Salmon, Salmo salar , Production Cages: Physical condition of cleaner fish stocked in cages. Journal of the World Aquaculture Society 45, 213–219.