Date Published: January 22, 2019
Publisher: Public Library of Science
Author(s): Julianne Valla Jacobsen, Klemet Steen, Kjell J. Nilssen, Caroline Durif.
Large numbers of lumpfish are produced for the Norwegian salmon industry and are used to combat sea lice infestations. Periodically high mortality of farmed lumpfish demonstrates the need to improve farming conditions and animal welfare. As part of such efforts, the present work tested the efficacy of three anaesthetic chemicals on lumpfish fries (average weight of 0.97 g). The anaesthetic impact from salinity (15 ppt–18 ppt), temperature (12°C versus 7 and 18°C), and fasting conditions (three days) was also examined. Surgical anaesthesia was induced within 3 to 5 min (preferred time) at concentrations of 18 mg/L (Aqui-S), 37.5 mg/L (Benzoak), and 60 mg/L (buffered MS-222). Safety margins were regarded as low when using Aqui-S; therefore, this chemical was not considered suitable for prolonged exposures. The lumpfish made a rapid recovery from both Benzoak and MS-222 even after 20 min of exposure. A 6°C increase in exposure temperature (reaching 18°C) was found to delay or inhibit recovery. The effect of a 5°C decrease (down to 7°C) significantly reduced induction time for MS-222 and was insignificant for Aqui-S, while it prolonged Benzoak induction time significantly and gave a longer recovery period. Fasting resulted in 70% recovery after 20 min of Aqui-S exposure compared to 0% in fed fish but had only minor effects on Benzoak and MS-222. Use of brackish water (15 ppt–18 ppt) gave 20% recovery from Aqui-S and significantly shorter recovery time from MS-222 exposure, while the effects on Benzoak were insignificant.
The Norwegian farming of Atlantic salmon (Salmo salar) has reached a yearly production of 1.2 million tons, representing a value of 7.2 billion USD . Salmon infestation by an ectoparasitic lice (Lepeophtheirus salmonis) has become a major challenge to this important industry. These lice result in impaired fish welfare, reduced fish survival, and high costs since delousing activities amounted to 309.6 million USD in 2016 (including indirect costs) .
The performed experiments were approved by the Norwegian Animal Research Authority (Mattilsynet)–identification number FOTS ID 11840. Laboratory protocol: http://dx.doi.org/10.17504/protocols.io.wg2fbye
The results from our studies suggest that both Benzoak (37.5 mg/L) and MS-222 (60 mg/L) gave satisfactory anaesthesia of lumpfish fries, had acceptable induction and short recovery times, and good safety margins. Acceptable Aqui-S anaesthesia resulted in a recovery time that was too long; thus, this chemical cannot be recommended for anaesthetic purposes in lumpfish fries. Reduced salinity and fasting had little influence on anaesthesia, but precautions should be taken to perform anaesthesia at the temperatures to which the lumpfish fry have acclimated. In order to optimize the anaesthetic protocol, further studies should include blood chemistry during- and following anaesthesia.