RAJAKARUNA, R.S.*; BROWN, J.A.: Significance of chemosensory cues learned during ontogeny in Atlantic salmon and brook trout

Imprinting or early learning of natal breeding sites can be best understood when we consider the life history of salmonids. Juveniles learn odours associated with their home stream before seaward migration and use these odour memories for homing. However, timing of imprinting is unclear. Some studies have shown that imprinting occurs during parr-smolt transformation. We studied the ability of parr of Atlantic salmon, Salmo salar and brook trout, Salvelinus fontinalis to learn and remember environmental cues. We changed the environment of the laboratory held parr during development by changing the diet. They were given a learning period to develop preferences for disparate environmentally based cues associated with different diets and then were tested to determine if they could discriminate between the new cues and the familiar early cues. After hatching a group of full siblings were fed with salmon /trout starter feed for three months after yolk sac absorption. Then they were divided into three groups and were introduced to two new diets. One group continued to be fed with the same diet. We carried out choice tests between the parr of the original diet group and the new diet groups. We found that early environment had no effect on the choice made by parr of both species. They did not affiliate with cues from the environment/diet they encountered during parr stage. Our results indicate imprinting of site-specific chemical cues does not occur during early ontogeny in these two salmonid species. In salmonids, imprinting may take place later in development either just before smolting or during parr-smolt transformation, or they learn a sequence of olfactory landmarks during migration.