The same experiment was conducted twice with fish from two hatcheries because of
the small number of individuals available from each hatchery at one time. Pejerrey for
the first and second experiments came from stocks maintained at the Yoshida Experimental
Station, Tokyo University of Fisheries, and a private farm, the Yasuda Fish
Farm, respectively. Both stocks were derived from fish originally introduced in Japan in
1966 and have been reared ever since in freshwater, except for occasional use of salts
during handling or disease outbreaks. Adult-size pejerrey were harvested by scooping
the fish from partially drained ponds ŽYoshida Experimental Station; mean"SE body
weight of 284.4"13.7 g and total length of 33.2"0.5 cm., or by encircling fish in
large tanks with a seine followed by size-grading ŽYasuda Fish Farm; 200"3.1 g,
29.2"0.1 cm.. The fish harvested in both cases had not been exposed to saline water
for at least 1 week before experimentation.