Feeder Fish

for the week of 4/21/99

Many keepers of large, predatory fish choose to feed live fish (most commonly goldfish, guppies or minnows) periodically. In some cases, the predator in question will not accept non-living foods, but more often, the aquarist considers live feeders a special treat, or enjoys watching the natural hunting and eating techniques. Any ethical dilemmas of this practice must be resolved by the individual hobbyist, but there are some practical considerations as well.

Feeders and disease. There is always some risk of disease transmission whenever any new fish are added, but inexpensive, mass-produced feeder fish are probably more risky than most. Feeder fish should be inspected for obvious signs of infection before purchase if possible, and certainly before introduction to the home aquarium. Exposure time should be kept to a minimum, which means that only enough feeders that can be consumed immediately should be added at one time. This is especially important if the feeder fish had previously been kept at a much lower temperature. Any remaining feeders purchased should be cared for properly, that is, well fed and kept in heated, filtered aquariums in order to avoid stress and infection.

Feeders and crowding. Many tanks containing large predatory fish are overcrowded to the brink of disaster already, and the addition of dozens or even hundreds of feeders can push them well beyond the margin of safety. Feeder fish consume oxygen and excrete ammonia in even greater quantities than longer-lived tankmates and it is not uncommon for tanks to chemically “crash” shortly after the addition of feeders.

Feeders and aggression. Some hobbyists are delighted and others dismayed to find that feeding live fish increases the amount of aggression among their predatory fish.

Feeders and nutrition. Feeder fish alone rarely constitute a complete and balanced diet, so other foods should be offered as well, and feeders may need to be withheld on occasion until spoiled fish begin to accept more standard fare. Another option is to “gut-load” feeder fish by giving them a last, high quality meal shortly before being offered.

Feeders and digestion. Some types of feeders (certain minnows, for example) have high fat content that leads to unattractively obese and poorly colored specimens. Others, such as goldfish, have large, hard-to-digest scales, which can obstruct proper digestion, leading to illness and death.

“Tip of the week” appeared regularly in 1999 and 2000.