Quote:
Originally Posted by jpeff31787
mathgeek, I guess you take some kind of ratio between length and weight to figure out "plumpness"? Just curious to how you do it. This assessment gets fairly in depth and confusing for the ones who just want to skim over the sciency part and go straight to results. lol
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The simplest way to understand "relative condition factor" is to liken it to BMI (body mass index) in humans. There is a formula that accounts for "normal" increases in weight with increases in length.
Actually relative condition factor in fish is a bit simpler. For fish of a certain species caught at a certain time of year, there is a formula derived from measuring and weighing thousands of LA fish (same species and time of year) for what the fish of that length is expected to weigh. This is called the "standard weight".
The relative condition factor is the actual weight divided by the standard weight for the length. A fish that should weigh 2.00 lbs (from the length) but actually weighs 2.10 lbs (measured) has a relative condition factor of 1.05 (5% over the expected weight). Another fish of the same species and length would also be expected to weigh 2.00 lbs, but if it only weighs 1.80 lbs, the relative condition factor is 0.90 (10% under the expected weight).
If the fish of a given species are fat on average, they are eating well and not having high stress levels. If the fish are skinny, they are not eating so well (or may be stressed).
In past publications, we've shown that this measure of plumpness can be used to study competition between species with the same forage base as well as to quantify forage overlap between different species.