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Returning fish safely

Returning fish safely
Fish fight particularly hard in summer and expend a lot of energy during the fight. Fish use red muscle fibres during normal day-to-day swimming, requiring a supply of oxygen-rich blood.
For more energetic swimming, such as to avoid a predator, jump a waterfall or when hooked by an angler, fish can employ white muscle fibres, which provide power and speed, and function without the need for oxygen.
When using white muscle, glycogen stored in their muscles is converted to lactic acid, and once all the glycogen has been used up the fish effectively runs out of power. The process of removing the lactic acid and restoring the glycogen reserves requires oxygen and time, and the fish must find somewhere safe to rest.
For this reason it is important that when fish are returned to the water after a fight they are held for a few moments in clean, oxygenated water, until they have the strength to swim off under their own steam. A fish released too soon can get its head stuck in weed or silt, where it will be deprived of oxygen and could die. Holding the fish upright for a few seconds before release reduces the risk of it getting stuck, and increases the chances that the fish will be able to free itself.