85. Feeding systems for trout are similar to those used for feeding salmon, either automatic or hand feeding. Trout also grow at different rates. As mentioned previously, little is known about the effect of spatial distribution of food and the relationship with growth rate and welfare. It is known that fish can be intimidated by others and that this can reduce feeding opportunity. Some fish may receive less food than others and the question asked in relation to salmon is equally pertinent to trout: does this or their size affect their welfare? This should be the subject of research.
86. Trout are fed proprietary diets in pellet form all their life . The pellets range in size from coarse powders for fry to 10-20mm pieces for adult fish. The pellets contain animal protein, oils and vitamins and are balanced with inert plant fibre filler. Additional vitamins, hormones, antibiotics and vaccines may also be incorporated into the pellets. Floating or slow sinking pellets are distributed by hand, by automatic feeder or by a combination of both.
87. Feeding levels follow guidelines laid down by the feed manufacturers to achieve good conversion efficiency. Early diets tend to be of higher calorific value (with more oil) than diets for older growing fish or for broodstock. The monitoring of early feeding by fry is important.
88. Trout are deprived of food prior to slaughter and before significant handling and transport procedures. The objective of food deprivation is to evacuate the fish's gut to improve the welfare of the fish during the necessary management procedures. Fish should not be deprived of food for any other reason. In warm weather trout may reduce their intake or stop feeding altogether so the amount of food provided should be decreased accordingly to avoid water quality problems.
89. Before transport it is current practice to deprive fish of food for 48 hours, or longer under cold conditions when gut clearance rates are low. This practice reduces faecal contamination of water in the transport tank and minimises the metabolic load when the fish are crowded together for collection before and during transport.
90. Prior to slaughter, trout are often deprived of food for some days. Depriving a farmed fish which has been fed regularly will normally cause some adverse effect on welfare. Though controlled food deprivation can be beneficial it should not be carried out as a matter of course. In order that the overall effect of the food deprivation on welfare is an improvement, any beneficial consequence must be sufficient to counterbalance any direct adverse effects. Food deprivation as a means of redressing the adverse effect of feeding an inappropriate diet is unacceptable.