Hello Baby Lake Trout!
BY CAREY EDWARDS, IRON RIVER NFH
The Klondike strain of lake trout entered the hatchery system in 1995 and originated from wild gametes collected from lake trout captured on Klondike Reef in northeastern Lake Superior. They are considered a “humper” strain as they live in water greater than 600 feet and “come up” to the reef to spawn. Hatchery stockings of this strain have been documented to perform well in deep water areas of Lake Erie.
Currently, Iron River National Fish Hatchery (NFH) has two mature captive lines that were created in 2003. These fish were spawned for the first time in 2008 but producing viable eggs proved to be problematic and unsuccessful. For the last five years, these fish and their eggs have been studied tirelessly. Spawning techniques, incubation methods and diet formulations have been honed and then honed again, with minimal success in improving survivability. Compared to other lake trout strains with greater than 70 percent eye-up success, Klondikes do not measure up, with a success rate averaging 3 to 35 percent. This equates to a lot of work and little to show for it. As the brood fish aged and reproductive capacity increased, the hatchery has had some small successes along the way. Two brood lines were created in 2010 and their eggs were successfully turned into production fish and stocked into waters of Lakes Erie and Michigan.
after eye-up. Credit: USFWS
This past fall, yet another study presented itself in collaboration with Penn State University involving the use of a chemical called luteinizing hormone releasing hormone analog (LHRHa). LHRHa is a synthetic compound similar in structure to the natural LHRH hormone in mammals. Through a sequence of events involving the pituitary gland and ovaries or testis, the end result can hasten the maturation of eggs during the final stages of egg production.
One line was chosen (A line) for the study with three treatments being administered; 10ug, 20ug, and saline (control) solution. 28 fish were randomly chosen from the population for each treatment group, marked with an identifying fin clip, weighed and injected with a dosage of “solution.” The following week, fish were checked for ripeness and spawned accordingly. All fish in the 10ug and 20ug groups were ready to spawn while about half of the control group needed an additional two weeks to complete maturation.
The next step in the study was to individually incubate a subsample of each female’s eggs to compare percent eye-up by treatment group. The remainder of each female’s eggs was pooled by treatment group and incubated. After eye-up occurred, each female’s eggs were evaluated, pooled by treatment group, and percent eye-up was calculated for individuals as well as the pooled groups.
The average eye-up for individual was as follows: 10ug=62.8%; 20ug=62.7%; control=51.9%. The results from the pooled treatment groups and fish not included in the study are as follows: 10ug=69.7%; 20ug=68.4%; control=51.5%; non-study A=32.4%; non-study B=35.4%.
The increased survival has allowed us for the first time in the hatchery's history to produce enough eggs to meet our production goals and all egg requests for Klondike Reef lake trout. With continued success using LHRHa, brood stock numbers could be tailored to open up resources for other Great Lakes restoration activities.