Petri Dish Incubation of Eyed Eggs from Rainbow Trout and Splake

Four experiments were conducted from 2004 to 2006 to evaluate different protocols for incubating eyed eggs of salmonids in petri dishes. In the first two experiments, which used eyed eggs from Erwin strain rainbow trout Oncorhynchus mykiss or splake (lake trout Salvelinus namaycush x brook trout S. fontinalis). dishes were loaded at either 10 or 20 eggs/dish and incubated at 10 degrees C. Water changes occurred every 3 or 7 d until complete hatch; for each species, one group of dishes received no water change. Survival to hatch was not affected by the number of eggs per dish or the frequency of water changes in either species. However, in experiments 1 and 2, hatch was significantly earlier in the dishes containing 20 eggs than in dishes containing 10 eggs, In the last two experiments, 15 eyed eggs from Shasta or McConaughy strain rainbow trout were incubated at either 10 degrees C or 12 degrees C; the water was changed every 3 d or not at all. Shasta strain eggs exhibited no significant difference in survival or time to hatch between any of the treatments. For McConaughy strain eyed eggs, survival to hatch was significantly greater at 10 degrees C than at 12 degrees C, but water change treatment did not affect survival. No significant differences in time (d) to complete hatch were observed between temperature treatments or between water change regimes. To successfully mimic vertical-flow incubation of eyed salmonid eggs in petri dishes, we recommend a density of no more than 15 eggs/dish; no water change is needed at a temperature Of 10 degrees C. Daily removal of dead eggs and hatched fry is also required.