Posted: Monday 14 February 2011
Wrasse, a green alternative for sea lice removal?
Commercial and research programmes are underway at MERL on the development of wrasse as cleaner fish for the control of sea lice on salmon. Wrasse are being used in commercial production cycles in Scotland and Norway as part of an integrated pest management approach and to avoid dependence on chemical lice treatments. Our aims are to develop a sustainable culture of wrasse that avoids having to take fish from the wild and to conduct research to optimise their use for best practice in terms of wrasse and salmon welfare.
Since May 2010, Machrihanish Environmental Research Laboratory (MERL) has been involved in a project within the former Machrihanish Marine Farms (MMF) cod hatchery to develop techniques for the large scale production of ballan wrasse (Labrus bergylta).
The project is a collaboration between the Institute of Aquaculture and Marine Harvest Scotland Ltd. The cod hatchery at Machrihanish has been developed by Marine Harvest and MERL staff to provide excellent large scale facilities for wrasse culture with over 1000 cubic metres of tank space. Paul Featherstone, (below) a former manager at Howietoun, was appointed in May 2010 as Project Manager, and is working with Andrew Denham, former deputy manager at MMF. Paul and Andy work closely with the Marine Harvest health team headed by Dave Cockerill MRCVS.
Approximately 250 large ballan wrasse have been caught by local fishermen and established in tanks at Machrihanish along with 500 goldsinny, corkwing, rock cook and cuckoo wrasse. The fish have been established on a 
diet of fresh mussels, nephrops, crab and squid and survival has been extremely good with all the fish settling in well. Wrasse cohabit socially in the artificial seaweeds and pipes that we have introduced to the tanks.
Wrasse or lipfish (leppefisk as they are known in Norway) are well known cleaner fish and they use their thick rubbery lips and rasping teeth to detach lice and other parasites from fish. It is eventually hoped that all of Marine Harvest's wrasse requirements will be produced at Machrihanish with any surplus sold on to the rest of the Scottish salmon industry.
A pilot run of several hundred juvenile ballan wrasse, carried out in October, demonstrated that they are similar to cod in their early stages and we have developed good protocols and indications of where problems may arise. One major issue being that weaning off live feed is much more difficult than was previously experienced with cod. The quality of juveniles produced so far has been very high but the juveniles do show marked behavioural changes during periods of their development. Overall, they are much less cannibalistic than cod and we feel that they are not "fish eaters" which might be deduced from their behaviour in the wild and currently available fish meal based diets may not be entirely appropriate.
A second and third run will start in March and May 2011 with a likely further run in October.
We are working very closely with Marine Harvest Labrus, MH's sister wrasse company in Norway, who achieved great success in 2010.
In November 2010 we initiated a KTP project investigating the fatty acid profile of wrasse eggs with the Institute of Aquaculture (IoA) nutrition team. Initial results indicated that they had different levels of arichidonic acid to that seen in cod. Dry fishmeal based diets, supplemented with ARA, are being formulated to address this issue. In our previous work with cod, this was shown to be essential for successful long term egg production. Each broodstock wrasse is extremely valuable, particularly the males, which in the wild form a tiny proportion of the population. Ballan wrasse are protogynous hermaphrodites and are all born female. In later life a small proportion become male and these males protect a harem of females. Thus, unlike with salmon, we hope to get many generations of wrasse juveniles from each parent and it is essential we get the nutrition correct from day one. Scott Stewart, an IoA graduate has been appointed to the post of KTP associate to work with some of these challenges.
In addition to the commercial production at MERL, we are planning research studies on efficacy of wrasse at lice removal, interactions with salmon, commercial techniques for goldsinny wrasse production, vaccines for wrasse and health and welfare of wrasse used as cleaner fish in salmon culture. We also hope to initiate a national breeding programme, if funding can be found, using the Institute's expertise in this field to try to avoid the pitfalls of inbreeding, which could happen if not vigilant due to the small number of males in the population.
MERL is already established as a world leading facility for development of new treatments for sea lice and we hope that this project will take control of sea lice one green step further.
For further information contact Derek Robertson (dar1@stir.ac.uk) or Dave Cockerill dave.cockerill@marineharvest.com