Abstract

Commercial diets available for the culture of various types of fishes carry a bacterial load. Dehydrated diets contain from 10³ to 10⁴ viable bacteria per gram, while moist diet contains in excess of 10⁵ per g. Although dry feeds can be stored at 20°C without an increase in bacterial numbers, storage of moist diets at 20°C results in a marked increase in the bacterial burden of the diet. Species of Bacillus are most numerous, especially in dry diets; however, many other species can be isolated. The isolation of Salmonellae from fish diets has also been reported.

Notes

Fish diets should not be left sitting around, even on the bottom of the aquarium because they support a wide variety of fish pathogens. Wet diets should be stored at 4°C or cooler. Dry diets may be stored at room temperature without bacterial problems; however, it is preferable to refrigerate them due to vitamin C instability.

Gaseous sterilization of feeds is recommended. Ethylene oxide has no effect on food quality and is not detrimental to fish.

The bacteria which grow in fish diets are generally the gram positive ones. The gram negative bacteria (most fish pathogens are gram negative) don't grow commonly in fish diets. Bacteria ingested by fish likely pass through their intestinal system without being retained. Thus fish diets do not seem to be important disseminators or causes of fish disease.