Condition index

The condition index in fish is a way to measure the overall health of a fish by comparing its weight with the typical weight of other fish of the same kind and of the same length. The condition index is its actual weight divided by its expected weight, times 100%. A fish of normal weight has a condition index of 100 percent. So if a tarpon, for example, has a condition index of 104 percent, that would mean it is above the normal weight for an average tarpon of that length. If a tarpon has a condition index of 92 percent, that would mean that it is thinner, or below the normal weight of other tarpon that length. The condition index depends on how much a fish is eating compared to the energy it has to spend to live, migrate, reproduce, and do its other activities. The condition index for fish is a simple measurement that can be used to provide important biological information that can then be used to make better management decisions.

Definition and Calculation

The condition index in fish is a way to measure the overall health of a fish by comparing its weight with the average weight of other fish of the same length and kind. To do this, a weight-length relationship that is published in a journal or a reliable report is used to make the comparison. Some weight-length relationships are for a group of the same fish from a certain location; others are developed from lots of data from different locations and represent a more general result. Some studies have enough data to develop separate weight-length relationships for male and female fish of the same species, and/or to develop separate weight-length relationships for different seasons of the year (e.g. Spring and Fall).