Immediately after hatching (sac fry stage):
* Yolk sac: The fry rely on the yolk sac attached to their bellies for nutrition.
As they develop (alevin stage):
* Zooplankton: Tiny, microscopic animals like copepods, cladocerans, and rotifers.
* Insect larvae: Smaller insects like midge larvae and mayfly nymphs.
As they grow larger (fry stage):
* Larger insects: Fly larvae, caddisfly larvae, and stonefly nymphs.
* Small fish: Other small fish species.
Factors that influence their diet:
* Water temperature: Warmer water increases metabolism and food requirements.
* Availability: The types of food available in the water body will determine what the fry can eat.
* Competition: Competition with other fish for food can influence the diet.
It's important to note that wild trout fry are very vulnerable to predation and need access to a diverse food source to thrive.