• When the embryos hatch, they have large yolk sacs that serve as their food source.
   

• Look for any odd-looking trout (two-headed, three-headed, unusual heart development, etc. These odd trout usually don’t survive and illustrate the principle of survival of the fittest.
   

• Alevin can survive in a Petri dish for short periods and can be observed closely under a microscope or by using a hand lens.
   

• Tank maintenance is simpler when the alevin are in the breeder box. Actually, the longer the alevin can stay in the breeder basket, the longer these hatchlings have time to learn to swim to the surface to feed.

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Swim Up Stage   (AKA “First Feed”) (4-6 weeks)
 

• The timing of “first-feed” is critical in young trout. Every year the single greatest cause of trout mortality occurs when teachers and their students “miss” the swim-up stage. The signs of swim-up are subtle, and especially teachers new to raising trout may have difficulty noticing them. A further problem is that the swim-up period doesn’t last long, perhaps only three or four days; and, if you don’t know when this is going to take place or happen to be away from your tank when it does, you can miss it entirely.

 

• Initially, alevin will “swim up” to inflate their air bladders—independent of the need for food. It is important to delay first-feed until the majority of fish have only a small slit of yolk visible. Research indicates that fish still have considerable yolk reserves when only a slit is present. Feeding too early is not advantageous to the fish and only creates a fouled tank environment. If you are in doubt, place a small number of fry in a clear glass beaker/jar to examine the ventral surface (belly) from below.  Refer to Appendix G for photographs.

 

• Here’s a link to a YouTube video about the swim-up stage that may also be helpful: https://www.youtube.com/watch?v=0VfuBYoeb8g.
   

• We have provided a spreadsheet with built-in formulas to help you either predict or control when swim-up occurs. 
   

• As yolk sacs disappear, some trout will start swimming to the top of the tank. According to one hatchery manager: “It’s my experience that small percentages of fish will begin to swim up continuously over a period of 3-5 days. I begin to supplement feeding when approximately 25% are up and gradually increase feed amount as the percentage increases. When you begin feeding, only spread a minuscule amount of the food near any swimming trout.”
   

• When you’re beginning to suspect that the alevin may be ready to swim up, raise the water temperature to 52 to 55 degrees and expose the tank to light for at least half an hour a couple of times a day. See if this stimulates their swim-up behavior.
   

• Once all fry are feeding eagerly, keep them in the breeder basket for at least two more weeks.
   

• Two or three weeks after all the fry have been feeding, reposition the basket so that one side is under the surface of the water. This will allow the more adventurous fry to swim out into the main tank.
   

• After the vast majority of fish have left the comforts of the breeder basket, you may unhook the basket and lower it gently to the bottom of the tank.
   

• If your water temperature is 40 degrees F or more, add Nite-Out II to your tank as often as once a week.
   

• Once all the fish have left the breeder basket, you can remove it from the tank. At this time, you can also remove the front foam insulation during the school day.