Temperature Protocols

 

While on the days before the eggs arrive, your tank’s water temperature should be close to that of the water at the hatchery, you will want to raise the water temperature over time. The key questions are when and how fast.

 

Why does temperature matter?
 

The rate at which trout develop at all stages—egg, alevin, and fry—is to a large extent a function of water temperature. Trout develop very slowly when water is in the 30s; they start to grow quickly when water hits 50 degrees. The rate of development also determines when trout will need to be fed. We call this the “swim-up” stage, a period of just a few days when, if you’re very attentive, you’ll notice subtle signs that your trout have used up their yolk sac and are looking for food.

 

One way to tell when your fish reach this stage is through visual observation. For those of us who don’t have a ton of experience raising trout, a far better approach is to use a measure called Development Index (DI) to estimate when the fish are at the “swim-up” stage. DI is based on temperature. Each day the water temperature is above 32°, a particular constant is added to whatever the previous day’s DI total was.

 

This can be tracked on a spreadsheet, which will allow you to control or predict  when swim-up takes place.

 

When your alevin reach the swim-up stage, you need to be around (a) to notice the subtle signs and (b) to feed the trout a tiny bit of food. So, one of the reasons for being very thoughtful about what temperature to set your chiller at is so you can be sure your trout don’t swim up when your school is on winter or spring break or while you’re away at a conference or over a long weekend, etc.

 

Over the years, our coordinators group has come to prefer what we call the “warm and fast” approach. Alternatively, some teachers have preferred to go “cool and slow.” Both approaches have been successful, but it seems that warm and fast approach results in fewer problems.

 

Here are two examples of the two temperature protocols that some teachers used in January 2023. The highlighted sections indicate when swim-up was expected to occur. Before your eggs are delivered you will receive an e-mail with specific temperature protocol recommendations.

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Temperature Protocol Scenarios for Predicting Swim-up

 

#1 Warm and Fast

 

• Eggs arrive on 1/9

• DI on that day is 44

• Tank temperature is 48 degrees F on 1/9

• Tank temperature is 52 degrees F on 1/10

• Tank temperature is 55 degrees F on 1/11

• Tank temperature stays at 55 F.
   

THEN
 

• DI hits 85.91 on 2/3  - Alevins are swimming up

• DI hits 92.78 on 2/7

• DI hits 99.65 on 2/11

 

#2 Cool and Slow

 

• Eggs arrive on 1/9

• DI on that day is 44

• Tank temperature remains at 44 degrees F through 2/16

• Tank temperature is raised to 47 degrees F on 2/17

• Tank temperature is raised to 50 degrees F on 2/27

• Tank temperature is raised to 53 degrees F on 2/28

• Tank temperature is raised to 55 degrees F on 3/1

 

THEN

• DI hits 84.51 on 2/28  -  Alevins are swimming up

• DI hits 93.10 on 3/5

• DI hits 99.97 on 3/9

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