Effects of Salinity on the Oxygen Consumption Rate of Juvenile Lumpfish (Cyclopterus lumpus) in the Laboratory
Rationale for seeking N.H. Sea Grant Development Funds:
The lumpfish (Cyclopterus lumpus) is a commercially important species in Iceland, Newfoundland and Norway, where it is harvested for its egg masses (roe) that is used for caviar. The fishery is quite lucrative, and lumpfish roe amounted to approximately $32 million in world sales in 2003 (Johannesson, 2006), with the majority of these sales going to France, Germany and the U.S. Recently, juvenile lumpfish are being used in the Atlantic salmon aquaculture industry as a “cleaner fish.” In this practice, cultured juveniles are placed in salmon pens where they feed on sea lice infecting the salmon (Imsland et al., 2014a, 2014b). This has been an important discovery for the aquaculture industry since it has eliminated the costs and environmental damage associated with chemical therapeutants traditionally used to control sea lice.
Although the lumpfish is an important commercial species as a source of caviar and as a “cleaner Fish” in the aquaculture industry, there is relatively little known about its physiological ecology and spatial distribution. Salinity is considered to be one of the primary environmental factors affecting the physiology, growth, distribution and survival of marine organisms (Chen et al., 1996). It is also highly associated with species assemblage (Gunter, 1956; Martino and Able, 2003), and is therefore an important variable influencing the composition of fish communities. The objective of this study is to examine the effect of environmental salinity on the oxygen consumption rate of juvenile lumpfish. Results will benefit those who wish to use lumpfish as “cleaner fish” for species (e.g. steelhead trout) raised in locations that experience low salinities. This objective fits the most recent N.H. Sea Grant Strategic Plan for Sustainable Fisheries and Aquaculture. Specifically, it will investigate the possibility of using lumpfish as a method of controlling sea lice in low salinity finfish aquaculture locations. Thus the research will explore and extend this innovative and emerging aquaculture practice, and contribute to the emerging steelhead trout aquaculture industry in New England.
Brief description of the work to be performed:
In April 2015, ~20 adult broodstock lumpfish will be captured with constantly tended, large mesh gillnets set nearshore, and brought to flowing seawater tanks in the UNH Coastal Marine Laboratory. Spawning pairs will be placed in individual 500 liter tanks, and allowed to spawn volitionally. Resultant larvae and juveniles will be raised for the experiments using standard techniques (Martin-Robichaud 1991; Brown et al. 1992).
Experiments will begin when the juveniles are approximately 2 to 3 months old and 20 to 40mm in length. All specimens used for experiments will be from the same parentage. Individuals will be acclimated to the desired salinity by slowly adding de-ionized fresh water over a 6-hour period to represent a tidal cycle. Temperature will be kept at approximately 17°C with a heater/chiller in a water bath, that contains the acclimation and respiration chambers. Salinity will be monitored using a YSI (Yellow Springs Instrument) professional plus, Once juveniles have been acclimated to the test salinity they will be transferred into a small glass chamber (approximately 600-750 ml) containing seawater at the desired salinity. The glass chamber will be plugged with a rubber stopper through which a Venier oxygen probe and temperature probe extend. Each experiment will last for approximately 30 minutes or until the oxygen level has decreased by 50%, After approximately 30 minutes, or when the fish begin to show signs of distress, the fish will be removed and step-wise returned to their original salinity preference of 30 parts per thousand (ppt). Oxygen consumption rates will be measured at 5 different salinities (10, 15, 20, 25, 30 ppt) with the 30 ppt treatment considered the control. Each salinity will be tested once on the same day, and each salinity will be repeated with 15 separate individuals, for a total of 75 fish throughout the experiment.
Results of this research will help lead to advancements in marine aquaculture. Sea lice infestation is a major problem in salmon farming since they can cause multiple hemorrhages, which in turn allow the entrance of disease pathogens (Bravo, 2009). Salmon farmers typically rely on chemical therapeutants to delouse the fish, but in this process may lead to increasingly resistant sea lice populations (Denholm et al., 2002). Moreover, these chemical compounds are toxic to the environment, and banned in most countries. Because lumpfish are showing great promise in the removal of sea lice from salmon, leading to a decreased usage of toxic chemical pesticides, there is great interest in their culture. This work will provide fundamentally important information to those interested in rearing lumpfish and/or salmonids. These experiments will hopefully provide a baseline for further research that will document the abundance and spatial distribution of lumpfish in nearshore habitats. This would provide insight into changes associated with anthropogenically-induced changes (e.g. ocean warming). Indeed the species is ideal for this purpose since it prefers cold water, and since its population dynamics, at least in New England, are unlikely to be affected by fishing mortality.
Once the salinity tolerance is known for lumpfish we can begin to relate this tolerance to their spatial and temporal distribution in the Great Bay estuary. To accomplish this, future research would sample 4 sites, spanning the natural salinity gradient, in the lower-, mid- and upper estuary, once per week from June to October. Multiple types of gear (otter trawl, plankton nets, dip nets) would be used to capture lumpfish of different sizes. Three replicate collections, with each gear type at each site, would be made. All captured fish will be identified, measured to the nearest mm, retained in buckets until all three samples have been completed, and then released in their collection location. At each sampling location we would record temperature, salinity, and dissolved oxygen. Catch-per-unit-effort at the different sites and dates would be used to describe their temporal and spatial distribution in the Great Bay estuary.
N.H. Sea Grant research indicates lumpfish have wide tolerance for water salinities in aquaculture operations
In 2015, N.H. Sea Grant researchers determined that lumpfish are capable of tolerating a wide variety of water salinities, which suggests they could function well as cleaner fish in finfish aquaculture operations that occur over a wide range of salinities.
Relevance: The lumpfish Cyclopterus lumpus is used in the Atlantic salmon aquaculture industry to help "clean" or remove damaging sea lice from the salmon. Despite its importance in aquaculture, little is known about lumpfish ecology and physiology when placed in different salinity levels for aquaculture purposes.
Response: In 2015, N.H. Sea Grant-funded researchers conducted laboratory studies to examine how salinity impacts the oxygen consumption of juvenile lumpfish. The fish were exposed to five different salinity levels, during which their oxygen consumption and behavior were observed.
Results: The studies indicate that lumpfish are able to tolerate salinities as low as five parts per thousand (ppt) and as high as 30 ppt with no signs of stress observed. These results suggest that lumpfish could function well as cleaner fish in finfish aquaculture operations over a wide range of salinities.