71. The design of feeding systems and the methods used to distribute food should be such that an adequate quantity of food is made available to all fish. Food delivery points are normally spread over two dimensions, or are even concentrated in one place, but the fish are distributed in three dimensions. Individual salmon grow at different rates. However, 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. Fish on the periphery of a cage, near the sides or bottom, may receive less food but does this or their size affect their welfare? These questions should be the subject of research.
72. Many devices are available whereby food is automatically delivered to fish in their holding facilities. Essentially a hopper filled with feed is provided with a mechanism that discharges set volumes at predetermined intervals. The mechanism may be driven by clockwork or electrical motors. Where electricity is needed a mains supply may be used (e.g. hatcheries) or power may be obtained from batteries (e.g. sea cages). Wind power may be used to drive a generator to maintain the charge of batteries or they may be routinely renewed and recharged ashore. Most automatic dispensers fan out the feed to distribute it over a relatively wide area to make food available throughout much of the tank or cage. Other hoppers discharge directly into the water below. Occasionally the timing system may be replaced by a rod which the fish may activate to feed on demand. In another type of system feed delivery is regulated electronically at a large central silo and carried by compressed air through pipes leading to each cage.
73. Feeding by hand remains popular as it allows a better evaluation of fish response and the choice of how feed is spread but it is labour intensive. Depending on the size of the fish, six to eight feeds may be given per day (post-smolt) but this regime would usually coincide with a feeding period from 05:00 to 22:00 hours, using two shifts of workers. With growth of the fish the ration size is increased but food is given less frequently; large salmon may be fed only twice a day but the hours of daylight available may extend the frequency. Manual feeding cannot be carried out if weather prevents access to the cages but in such conditions the fish lie low in the cages and may not respond to feed. After such a spell an enhanced ration may be fed but this will be a local management choice.
74. The feed is usually in a pellet form ranging from "crumb" size for fry through a selection of sizes up to 10mm diameter pellets for the biggest fish (broodstock). Fry should be carefully monitored during early feeding as this is a crucial stage in their development. Once the fry start to feed the aim is to maximise growth for the largest number of potential smolts. The proprietary feeds are a mixture of fish meals and fish oils with binders and possibly a cereal content such as bran. The proportions of these ingredients are varied according to circumstances. The pellets are classed as having normal, high or super fat content. Some farms produce their own feeds on site from commercially caught fish and can determine their own mixtures. Vitamins, trace elements, pigments and growth enhancers may also be included. Pellets sink into the water column or can be manufactured to float on the surface. Some producers use a wet feed system which introduces feed mixed with water through pipes into the cages.
75. To increase the probability of all fish receiving food it is necessary to grade them to reduce disparity caused by size, provide sufficient food for all fish, offer the correct size feed and regulate stocking density.
76. Fish are deprived of food before certain essential management procedures are carried out (e.g. prior to transport, treatment of disease and transfer of smolts from fresh water to sea water). The objectives of food deprivation are to evacuate the fish's gut and to reduce oxygen demand and waste production in order to improve the welfare of the fish during the management procedure. Farmed fish should not be deprived of food for any other reason.
77. Smolts are deprived of food prior to transfer to sea primarily to reduce oxygen demand during transport. However, the stress associated with transport is reduced by lowering the fish's metabolic rate.
78. 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.
79. Prior to slaughter, salmon are often deprived of food for some days or weeks. In the wild, salmon cease to feed prior to breeding and are adapted to food deprivation at this time. However, 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.