Seawater Acclimation of Juvenile Steelhead Trout (Onchorhynchus mykiss)

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W. Huntting Howell UNH - Department of Biological Sciences Principal Investigator
Michael Chambers N.H. Sea Grant Co-Principal Investigator
Erik Anderson Commercial Fisherman Industry Partner
Vincent Marconi Commercial Fisherman Industry Partner
William Marconi Commercial Fisherman Industry Partner
C. Marconi Commercial Fisherman Industry Partner
Chesley Severns Commercial Fisherman Industry Partner
J. Ford Commercial Fisherman Industry Partner

Students Involved:

Michael Chambers N.H. Sea Grant
Jonathan Bunker UNH - Department of Biological Sciences

Brief description of the proposed work

Steelhead trout (Onchorhynchus mykiss) are the anadromous variant of rainbow trout. The species has been domesticated for >150 years, and is the basis for extensive commercial marine aquaculture industries in Canada and northern Europe. In recent studies, funded by the Norwegian government and by NOAA/NMFS Saltonstall-Kennedy, we studied the ability to grow steelhead in submerged cages and their behavioral responses to net deformation. In the course of these studies, we found that they have several attributes that make them an ideal candidate for marine aquaculture in northern New England, but we did not have the opportunity, or funding, to study how best to acclimate the fish from their freshwater hatchery environment to seawater.

It is worth noting that six commercial fishermen, all interested in exploring marine aquaculture, assisted with the previous research, thereby giving them both experience and training on the techniques of steelhead trout aquaculture. As a result, all six have applied for New Hampshire aquaculture permits. Results of both the previous and proposed research thus fit each of the objectives listed under the Sustainable Fisheries and Aquaculture, Research Goal 2, in the N.H. Sea Grant Strategic Plan. We have identified a very promising marine aquaculture species for New Hampshire, and we are helping New Hampshire fishermen develop aquaculture practices that are both economically viable and environmentally sound.

One observation we, as well as commercial growers in Canada, have made over three years working with this species is that a portion of the cultured population (~10%) is stunted. This results in: (1) difficulty in the harvesting schedule because not all individuals are ready for market at the same time; and/or (2) loss of a portion of the crop if some individuals never reach market size.

We are interested in finding the cause(s) of stunting, and trying to minimize or eliminate it. One potential cause relates to acclimation of the fish from their freshwater hatchery environment to seawater. In nature, juvenile steelhead trout migrate from freshwater rearing habitats, through estuaries, to ocean environments -- a process that can take from weeks to months depending on the strain of steelhead. During this migration they undergo smoltification, a complex morphological, behavioral and physiological process that alters their appearance, behavior, and their osmoregulation from ion retention to ion excretion. In contrast to the gradual transition from fresh, to estuarine, to salt water that occurs in nature, cultured steelhead are typically moved from a freshwater hatchery directly into seawater, which may impair physiological functions in some individuals, and cause them to be stunted.

We propose to test the hypothesis that the rapid transfer of steelhead from fresh to salt water (no acclimation) can result in stunting. Further, we hope to determine if the length of time spent in estuarine (low salinity) conditions affects the proportion of stunted individuals. In a subsequent Sea Grant proposal, we plan to hold steelhead in replicate cages near the Jackson Estuarine Lab for varying lengths of time before moving them to the coast, and compare their survival, growth, blood chemistry and size frequency distribution to fish moved directly into seawater with no acclimation.

If fortunate enough to be funded by N.H. Sea Grant, the funding would not be available until 2014. We hope to gather some preliminary data in 2013, refine our methods, and work on the logistics of holding the fish at two different locations. Accomplishing this work would ensure our chances of success in the full proposal. Further, the supplies we purchase this year would decrease our budget request in the full proposal.

Our plan for 2013 would include purchasing 1000 steelhead trout (200g average weight) in late April. This number is needed since we see a small proportion of stunted fish, and we need to ensure an adequate sample size of small individuals. Half the fish would be held in a small net pen located in the estuary near Jackson Lab, and half the fish would be located in a similar net pen at the Judd Gregg Marine Research Facility. Temperature and salinity data loggers would be attached to both net pens to record these environmental variables. Fish would be fed 5% of their body weight in two daily feedings, and the number and size of any mortalities would be recorded. On the first day, and at weekly intervals thereafter, a random sample of fish from each location would be anesthetized, weighed, and measured. On the same schedule, a blood sample (caudal vein) from a random sample of 20 individuals would be obtained, and blood osmolarity would be measured. At the end of three weeks, fish held near JEL would be moved by boat (estuarine water in insulated containers) to a separate net pen at the coast. Sampling of length, weight, survival and blood chemistry would continue, for both groups of fish, over the following three weeks.

This project would give us good preliminary data on the value of acclimation, and allow us to work on the logistics of maintaining fish at a new location Great Bay (e.g. mooring a cage, feeding the fish twice per day).

As indicated, we have been working with six commercial fishermen on steelhead trout aquaculture over the last two years. In order to continue our outreach goals and support of this group, they would participate in this preliminary research, and we would donate the fish to them, for on growing and marketing, when we completed our studies.

2013 Accomplishment

Stepwise acclimation lessens mortality and stunting in trout moved from hatcheries to open ocean aquaculture
N.H. commercial fishermen are raising steelhead trout in aquaculture pens to augment their income, but some of the trout have experienced stunted growth when transferred from the hatchery directly to seawater. With funding provided by a N.H. Sea Grant development grant in 2013, researchers developed a protocol for stepwise acclimation of steelhead trout during stocking to help them adjust from freshwater to low salinity (estuarine) water and then to high salinity (sea) water and conducted studies to determine if stepwise acclimation would lead to improved growth and survival. Sixteen percent of the fish transferred directly to seawater were stunted after three months and experienced higher mortality rates, while only three percent of those held in the estuary prior to stocking in seawater were stunted and experienced lower mortality rates. These data suggest that a stepwise acclimation protocol from freshwater to estuarine and marine waters may be beneficial to trout growth and survival. Although more research is necessary, these preliminary results suggest that salinity is an important factor to consider when designing an acclimation protocol for trout aquaculture in the open ocean environment.


Chambers, M. (2013). Research and development of steelhead trout Oncorhynchus mykiss aquaculture in sea cages. Doctoral dissertation, University of New Hampshire.