Fish Hatchery Management - fisheries & aquaculture

176 FISH HATCHERY MANAGEMENTERMINAL DISCA. ONE DAY AFTER FERTILIZATION, 559'F AVERAGE TEMPERATURE(23.9 T.U ).LASTODISCB. TWO DAYS AFTER FERTILIZATION, 53.9"F AVERAGE TEMPERATURE(43.9 T. U.)DGE OF BLASTODISCMBRYOC. FIVE DAYS AFTER FERTILIZATION 5i.7'F AVERAGE TEMPERATURE(98.4 T. U.)FIGURE 61. Schematic development of trout and salmon eggs. One temperatureunit (TU) equals 1'F above 32'F for a 24-hour period. See Glossary: Daily Tem-Derature Unit. (Source: Leitritz and Lewis 1976.)When small numbers of eggs are involved, counting can be done byhand or by the use of a counting board that will hold a known number ofeggs. A paddle-type egg counter is constructed of plexiglass by drilling andcountersinking a desired number of holes spaced in rows. The diameter ofthe hole will depend on the size of eggs being counted. The paddle is