Degree Day Marks during Embryogenesis of Oncorhynchus mykiss and Oncorhynchus Clarkii Clarkii

Degree days (DD) are used to describe ontogeny of fish species. In practice DD can be applied in aquaculture and in climate change research. This study tracks developmental stages of Oncorhynchus mykiss (TRR) and Oncorhynchus clarkii clarkii (ONC). Eggs were housed in heath tray incubators using four fertilization dates (treatments) of each species with a minimum of two replicates per treatment. Temperatures were monitored hourly and every ten minutes by using two data loggers. DD was calculated as: DD=∑│average daily temperature (°C) │ for each observed developmental stage. Preliminary results suggest the following average DD marks: “Visible neurulation”(TRR: 99.4; ONC: 101.), “weak eye pigmentation” (TRR: 172; ONC: 173), “eyed egg”(TRR: 222; ONC: 216), “spinal pigmentation” (TRR: 306; ONC: 291), “start hatch”(TRR: 317; ONC: 300), “end hatch” (TRR: 382; ONC: 312) and “swim up” (TRR: 481.5; ONC: 462.8). This is the first study that determines DD marks for ONC. Previous studies on TRR report different developmental DD marks. This suggests that visual observations during development can be subjective and that there is the need for defined classification systems. Species-specific definition of observable development stages and temperature tolerance ranges during embryogenesis could help predict effects of climate change on individual fish populations.