Escape speeds of marine fish larvae during early development and starvation

Abstract

Response rates to tactile stimulation and subsequent escape speeds were measured using a video-recording system during early development and starvation of fish larvae. The species studied included the yolk-sac larvae of Clyde and Baltic herring (Clupea harengus L.), cod (Gadus morhua L.), flounder (Platichthys flesus L.) and older larvae of Clyde herring. The proportion of larvae responding (response rate) was initially about 20 to 25% in herring and 35 to 40% in cod and flounder using a probe, but about 70 to 80% using the sucking action of a pipette in all species except flounder. Both response rates and escape speeds (mean and maximum) tended to peak 1 to 2 d before the PNR (point-of-no-return, when 50% of larvae are too weak to feed), then decreased slowly during further starvation. An inter-species comparison showed that the highest recorded mean escape speeds (measured over a period of 200 ms) and highest maximum escape speeds (over 20 ms) ranged from 5.7 to 8.6 BL/s (body lengths/s) and 12.1 to 16.1 BL/s, respectively. The larvae made directional responses away from the stimulus only when they developed and reached the feeding stage.