We have used Musca domestica for fish food successfully off and on for over twenty years. These applications have included live, dried, and frozen larvae and pupae as well as a custom made fry ration. The fish fed in these applications were various fresh water aquarium fish, pond raised trout, laboratory raised salmon and koi.
The aquarium fish most closely observed were Discus and Oscars, although several dozen species have been tested with the insects. All of the fish seemed to find the insects palatable and digestible and had no initial difficulty recognizing the offering as food. It was determined that live or frozen larvae would be of particular use as a food source for Oscars from one to three inches. The Discus were fed dried larvae "gut loaded" with canthaxanthin. Over a period of several weeks, the colors of the fish improved considerably with particular enhancement of the reds.
Rainbow trout, hatched and grown for commercial fishing ponds, grew rapidly on dried larvae and an experimental fry food. The free swimming fry grew to an average length of three inches in sixty days. The mortality rates during the trials were one tenth of that reported by the hatchery when compared with rearing cycles using similar procedures with their standard foods. The duration of their standard rearing cycle with regular food was ninety days to achieve the same three inch length.
Our firm provided dehydrated insects for nutrition and growth rate experiments by the US Bureau of Fisheries Colombia River Research Station. The results were reported as positive. Other Northwest researchers have speculated that the introduction of the insects to the hatchery raised fish before their release into wild waters would familiarize the smolt with the smell, look and taste of natural foods thereby enhancing their viability. Frozen loaded larvae may be useful in hatcheries for substance delivery.
Our experience with koi spans a little more than five years. Most of the feeding has been in test tanks and lined pools. The insect materials studied consisted of plain and loaded dehydrated larvae and frozen loaded larvae. Although we were actively watching the progress and results of the koi trials, we did not perform the work. Studies done in England reported that it was apparently not possible to feed so much of the canthaxanthin loaded larvae that the fish were harmed. Japanese researchers have allowed possible benefit from their use and continue observations.