November 26, 2012 at 9:41 am
As crisp mornings become regularly bedecked with heavy frosts, landlocked salmon have one thing on their minds: spawning. For the most part, salmon are quite able to locate an appropriate spawning area, spawn, and return back to lakes and ponds without any issue. But for those that meet up with MDIFW hatchery and fisheries staff who are working to manage salmon populations statewide are re-routed a bit.
To maintain the landlocked salmon population in waters where there is either intense angling pressure on wild salmon, or no spawning grounds, MDIFW raises landlocked salmon and then stocks them out. This might sound like a pretty easy process, but not when the scale of it is around 105,000 salmon stocked each year! Thankfully, our hatchery crews are well trained and experienced; MDFIW has been stocking landlocked salmon in waters across the state since 1895. Still think it should be pretty simple? It’s not, and there’s actually a science behind raising and stocking healthy fish year after year.
As with any breeding program, the key to keeping each year’s offspring healthy is genetic diversity. How do you do that in a hatchery setting? You mix and match the fish you take eggs and milt (fish sperm) from, breeding fish from different age classes. Our hatcheries do this by artificially spawning healthy salmon from some of the major lake systems in the state. When the salmon run, some of them are diverted into fish traps, like the one I had the opportunity to visit near Sebago Lake. They are sorted by sex and age by hatchery personnel and are checked for readiness to spawn. Once they are ready to spawn, hatchery personnel gather at the fish trap. They place four to five males and females at a time into separate tanks which contain water treated with an anesthetic. This anesthetic makes the fish easier to work with, and relaxes their muscles, making the artificial spawning process safer and less traumatic for the fish and the fish handlers. First, an anesthetized female is chosen. She is removed from the water and “stripped” of her eggs into a bowl designated for that purpose. Then she is transferred to fisheries biologists standing by who will collect data on length, weight, and injuries and marks. This information helps the biologists determine the health of the salmon population in the body of water from which the fish came. The biologists then release her down a “fish chute” back into the river. The anesthetic will wear off in 1-20 minutes, depending on the length of time she was in the anesthetic-enhanced water. Then an anesthetized male is selected. He is removed from the water and the hatchery personnel add a couple squirts of his milt to the bowl containing the female’s eggs. The male goes through the same process as the female before him with the fisheries biologists. The eggs and milt are mixed and allowed to set for a few minutes while the eggs become fertilized. Then a small aliquot (sample) of eggs is taken from each mating’s donation, designated to become brood stock, or breeding fish, at the hatchery in 3 years. A sample of ovarian fluid and milt is taken to send off to the MDIFW fish pathology lab, to be tested for any bacteria that might be in the eggs and/or milt. Then the eggs are placed in water, which will cause them to ‘harden’ and become more resistant to external influences.
At the end of the day, the fertilized eggs are brought back to the hatchery where they will undergo external disinfection using a specific iodine solution. This does not harm the eggs as they have already fertilized and water-hardened and will not take in anything else from their environment as they develop. Disinfecting the eggs is an important step in raising landlocked salmon, because potential diseases or fungus brought into the hatchery from the lake environment could potentially negatively affect the sac-fry when they hatch. The eggs are enumerated and laid out in a single layer on egg trays set into aluminum troughs, with water flowing over them to simulate incubation in a stream.
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