Intraspecific pheromone discrimination and substrate marking by atlantic salmon parr

Attraction and preference behavior patterns shown by Atlantic salmon (Salmo salar L.) parr towards intraspecific odors were measured. Salmon parr were attracted to tank water in which relatives of their own strain were held but were also attracted to tank water containing another strain of their species. When given a choice between the two types of tank water, water containing their own strain odor was significantly favored over water containing conspecific but nonfamiliar odor, revealing that pheromones are present at intraspecific levels in salmonid juveniles. Competitive experiments with various extracts suggest that the active compounds are most likely produced in the liver and are voided via the intestinal tract, as determined by presence of attractants in intestinal contents and bile. Intraspecific discrimination was not detected with extracts from either skin surface mucus or blood plasma. Extracts from gravel that had been kept below the fish in their rearing tanks, however, induced a strain-related preference behavior. This suggests an ability for substrate marking by salmonid fishes, presumably mediated by deposition of fecal material. Strain discrimination and substrate marking are discussed in relation to stationary behavior and homing of fishes within discrete populations in natural systems.