Abstract

Ensuring lumpfish health and welfare in salmon farms is vital to reduce the high mortality rates reported and to guarantee a high delousing efficiency. Recent observations of farmed lumpfish livers have shown colours ranging from pale (colours 1 and 2), through bright orange (colours 3 and 4), to dark reddish-brown (colours 5 and 6), some of which may be related to welfare condition. To characterize the status of lumpfish deployed in four Faroese salmon farms, several welfare indicators were assessed: a weight-length relationship, scoring of external physical damage, and after dissection, stomach content and liver colour scoring. Liver samples were weighed, stored and analysed for lipid content, lipid classes, total pigments, fatty acid profile and histopathology to explain the differences between the mentioned liver colours. Bright orange livers, liver colours 3 and 4, were related to increased levels of carotenoid pigments rather than levels of lipids and appear to reflect good fish welfare. However, dark reddish-brown colours, liver colours 5 and 6, were associated with very low levels of triacyl glycerides in the liver, indicating use of lipid reserves and poor welfare condition. Histopathology confirmed that the dark reddish-brown livers, liver colours 5 and 6, formed a distinct group. Thus, liver colour was shown to be a good welfare indicator and should be monitored in farms.

Highlights

  • Sea lice have been a serious problem in the Atlantic salmon farming industry since the 1970s1

  • Several parameters have been investigated to help expand the limited knowledge on welfare of the species, such as behaviour in pens[17,18], coexistence with salmon[17], food preferences[19,20] and delousing efficiency[19,21,22,23,24,25]. In some of these studies it was observed that farmed lumpfish shows a wide range of liver colouration, and they were classified in six different liver colours, ranging from very pale to dark reddish-brown[24,25], in contrast to the orange colour displayed in livers sampled from wild lumpfish

  • The proportion of bright orange livers increased with size and was dominant, i.e. 62%, when the lumpfish were larger than 100 g (Fig. 1)

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Summary

Introduction

Sea lice have been a serious problem in the Atlantic salmon farming industry since the 1970s1. Several parameters have been investigated to help expand the limited knowledge on welfare of the species, such as behaviour in pens[17,18], coexistence with salmon[17], food preferences[19,20] and delousing efficiency[19,21,22,23,24,25] In some of these studies it was observed that farmed lumpfish shows a wide range of liver colouration, and they were classified in six different liver colours, ranging from very pale to dark reddish-brown[24,25], in contrast to the orange colour displayed in livers sampled from wild (and presumably healthy) lumpfish

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