Fish Fry Growing

ArrayApril 2, 2013 at 3:33 pm

First and foremost, before we get into some fishy talk, I’d like to apologize for my absence on this blog the last several weeks. I have switched positions, headquarters, and many duties within MDIFW and will continue to post about three entries I hope you find interesting every month. I am fortunate that with my new position, I will continue to work with the hatcheries division, fisheries division, and wildlife division, and will attempt to keep the blog entries diverse. Now that I’m all settled in again, let’s talk fish! As you may recall, my last entry about the brook trout developing at Dry Mills Hatchery in Gray talked about fish eggs, how they are taken from spawning fish in a hatchery environment, and how they develop. Now, 11 weeks later, I am happy to report the fish have all hatched at the Dry Mills Hatchery. The Maine Hatchery Strain (MHS) fish are growing very rapidly. The strain refers to the genetic make-up of the fish, and typically relates to where they originated from. The Maine Strain fish are related to the brook trout that have been raised from the Maine hatchery systems for years. The Kennebago strain refers to fish who originated in the Kennebago River in the Rangeley Lakes Region. Cross Strain refers to hybrid brook trout that have one Maine Strain parent and one Kennebago Strain parent. The Maine Strain fry have absorbed the yolk nutrient sac they hatched with and are now eating a powdery fish food. They are fed for 18 hours every day, using belts suspended over the tanks which dispense food measured previously. The belt feeders provide ample time for each fish to have its fill and grow. The amount of food that should be provided is determined by the average weight of the fish and how many fish there are in each tank. It would be far too tedious and stressful on the fish to weigh each fish individually when they are fry (the term for fish that are between hatching size and approximately three inches long), so they are weighed in batches of 100 to 150 fry. Some quick math calculations tell us that the MHS fry currently weigh approximately 0.2 grams each. Sure they seem small now, but they will double in size in the next two weeks. The Kennebago strain is the most wild fish strain currently being reared in Maine’s hatchery system. While Kennebagos provide a good fight when they are large, stocked, and then caught, their wild personality inhibits their growth in the hatchery setting. Kennebagos tend to be more easily spooked than the MHS. They become stressed more easily, which affects their appetite, which affects their growth. The Kennebago fry currently at Dry Mills have recently depleted their nutrient egg sacs and are beginning to rise in the water column in the tank, indicating they are ready to begin to eat mash fish meal. When hatchery personnel begin to see some of the fry rising in the water column, they hand feed small amounts of ‘mash’; they must be very careful not to over feed, as any leftover food will settle to the bottom of the tank and will likely be snarfed up by sac-fry which do not have the ability to digest the food yet, or the excess food may clog the gills of fish sitting on the bottom of the tank and create a suitable environment for a fatal bacterial gill infection. Typically within one week of the earliest fish rising, all of the others will be ready to feed on the ‘mash’, and they will begin to double in size in two weeks. Then they will double again in another two weeks. By spring, they will be ready to be moved from their indoor tanks to the outside raceways. Meanwhile, spring yearling brook trout, measuring roughly 9-12 inches in length, are growing steadily in the outdoor raceways. They are being fed once daily, and are ready to be stocked in the spring. [embed][/embed]