Physics and Fish Bioenergetics

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Welcome to the world of fish physics. Many of us understand basic fish behavior and can reach logical conclusions about where the best place to throw a fishing line is. But when we don’t think much further than that we are missing out on some very interesting details of fish behavior. We can never fully understand why we find some fish in one location and some fish in other locations until we consider the concept of fish bioenergetics. Ultimately, fish behavior is a product of bioenergetics. First, we will take a look at basic fish bioenergetics, understanding the underlying quantitative principles. Then, we will look at some examples of how physical forces, thermodynamics, and light characteristics are specifically related to fish bioenergetics. Most of these models and ideas are made under the assumption that there is no predation or competition, which are additional factors that will influence behavior.

Fish bioenergetics includes components of physical forces, thermodynamics, and light characteristics, and follows energy laws and theories describing any other closed system. What it all boils down to is the net rate of energy intake. If this rate is positive a fish will grow and if it is negative then a fish will begin to undergo the stresses of losing biomass.

Fish bioenergetics is really a matter of efficiency. Potential profit for a fish at any given position in a stream is simply the amount of energy coming into its system as prey minus the cost of staying at that position. This simplified model can be desribed by

P = D - S

where P is potential profit (calories/hour), D is available drifting invertebrate energy (calories/hr), and S is swimming cost (calories per hour) (Fausch 1984). For example, th...

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