The issue of whether fish should be kept in keepnets has been a burning one for quite some time, with some anglers either completely avoiding their use, or others using them regularly and/or permanently. The major reason why some anglers don’t use keepnets is the potential risk that fish experience vastly greater amounts of stress, or are physically injured and thus more likely to die after release. These are certainly good reasons, but given that competitive angling requires bags to be kept and weighed, the question still burns about whether keepnets damage fish or not.
Fish do experience some stress when they are caught using rod and reel. The natural response of the body is to secrete a stress hormone known as Cortisol. Cortisol is released by the kidney when the brain of the fish registers a form of stress. Thus, measuring blood cortisol levels is currently one of the most commonly used techniques by fish biologists to determine stress. It might come as a surprise to some, but carp actually experience very moderate amounts of stress when they are kept in keepnets that are made using fine, knotless material, but definitely NOT the steel mesh or coarse knotted mesh kinds. (In fact, steel mesh keepnets should be banned completely!).
Studies that have been carried out specifically on carp have shown that fish increase their cortisol secretion when caught, and which peaks roughly within 4 hours after them being caught. Of significance is the fact that when these same fish were kept in acceptable keepnets, their cortisol levels started to drop and reached levels that were no different from fish that had not been kept in keepnets at all! This means that fish which are retained responsibly by anglers in a carp care keepnet actually calm down and don’t try frantically to escape the net all the time. In a different study, scientists kept fish that had been caught with rod and reel in large keepnets to determine whether fish lost weight or died when kept in keepnets. Even though fish were kept inside these holding nets over a period of two months they did not feed less or grow slower than fish that were not kept in keepnets. This clearly indicates that keepnets are not the extremely cruel confinement devices that some people make them out to be.
Although the use of a correct keepnet is not a cruel and unusual practice, there are some serious considerations when they are to be used. These include the mesh type, placement of the net and the size of fish.
Firstly, the mesh type is extremely important. To stress fish as little as possible you need to use smooth, knotless mesh that is soft and has a small mesh size. Fine rubberized mesh is also very good. This type of mesh has several advantages, including one that I believe is most important, namely that it creates a shadow around the fish which makes it feel sheltered. For that reason it is also a good idea to keep fish in a net with a relatively darker mesh type. Part of the stress that fish might feel when they are in a keepnet is not the net itself, but the fact that they feel exposed and are being kept in an environment where the light intensity is much greater. Another important consideration is the placement of the net. A keepnet with fish in must be placed relatively deeply, at least more than 700 – 800mm of water (just under one metre). This ensures that water moving through the net is not overly warm and is also well oxygenated. It also provides some room for the fish to adjust its position and to move to a comfortable temperature.
The size of fish that are kept in nets is an important determinant of the stress they may experience. Large specimens should be released immediately; in fact there is no reason to keep them in a keepnet at all. Large fish should be handled carefully for several reasons – firstly a large specimen that is in good condition is not just a good, heavy fish, it is also an animal of high genetic value! Smaller fish (5kg and less) have a high gill surface to body mass ratio, meaning that they can recover from hooked stress relatively quickly. The small body size also means that they can move around freely inside a keepnet and they generally survive very well in keepnets. Larger carp however face many problems if they are confined in keepnets, particularly fish of 6kg and heavier. The large body size means less space to move around, meaning that large fish are bumping into the net more frequently; they also move around with more force and either rub their fins raw (also known as “red tail”) or manage to skewer their fins through the mesh and so become entangled. Major causes of fish deaths after carp have been released from a net are actually fungal and bacterial infections to their gills and skin, so any risk of scraping injuries must be minimized.
HINT: The skin of fish has a protective layer of mucous, some of which unavoidably rubs off on the net which can cause the net to become quite smelly after a while. An effective and easy treatment to counter this is to spray the net with vinegar after every fishing trip and to leave it dry thoroughly. Another highly effective treatment that also rids the net of any harmful bacteria is to wash the net in a chlorine bath (ordinary Jik is excellent).