Functional consequences and population differences in the developmental plasticity of muscle to temperature in Atlantic herring Clupea harengus

The development of the axial muscles was investigated in Atlantic herring C lupea harengus from 2 spring-spawning (Clyde and Blackwater) and 1 autumn-s pawning (Manx) populations in 2 successive years. The results indicate sign ificant developmental differences between stocks. Myofibril synthesis and t he development of acetylcholinesterase activity at the neuromuscular juncti ons occurred later with respect to embryonic stage at 5 degreesC than at 8 and 12 degreesC in Clyde herring, with much less pronounced differences bet ween temperatures for the other populations. In a second series of experime nts, Clyde herring were incubated at 5 and 12 degreesC until shortly after hatching, and then reared at ambient temperature in triplicate tanks. The 5 degreesC group had a faster growth rate than the 12 degreesC group with re spect to effective day-degrees from hatch. However, flexion of the notochor d and the development of the dorsal and anal fin ray muscles occurred at sh orter body lengths in the 12 than 5 degreesC groups. The maximum escape vel ocity of larvae during fast-starts was determined using a high-speed video. Over the size range 11.2 to 18.5 mm total length, the adjusted mean maximu m velocity was 24% higher in larvae hatched from 12 than 5 degreesC eggs. C ruising swimming behaviour also differed between groups with the 12 degrees C larvae showing reduced yaw relative to the 5 degreesC larvae, indicating a more developmentally advanced sub-carangiform style of locomotion.