Temperature effects on larval survival, larval period, and health of hatchery-reared red king crab, Paralithodes camtschaticus

Abstract

We tested the effects of two rearing temperatures (8 and 11°C) on survival, larval period, and health of red king crab (Paralithodes camtschaticus) larvae in eight hatchery-scale 1200L tanks as part of a stock enhancement feasibility study. Larvae were stocked at a density of 50larvaeL−1. Survival did not vary from the newly hatched first stage zoea to the glaucothoe and first juvenile crab stage (C1) between the two temperatures. Survival averaged 50% from stocking to the glaucothoe stage and 20% from stocking to C1. Overall, 480,000 Z1s were stocked and 96,200 C1s were produced. Larval periods were significantly shorter at the higher temperature, averaging 21days from stocking to glaucothoe and 35days from stocking to C1 at 11°C compared to 30days to glaucothoe and 50days to C1 at 8°C. Specific attributes of larval health measured in this study included the size and relative number of lipid droplets in the anterior region of the larval gut as a measure of stored energy reserves and percentage of the surface of the larval exoskeleton fouled with filamentous bacteria. Quantitative assessment of accumulated lipids as measured by maximum lipid droplet diameters and relative numbers of lipid droplets in the anterior region of the gut was not significantly different between larvae reared at the two temperatures, suggesting that larvae were able to accumulate similar quantities of lipid energy reserves at both temperatures. Filamentous bacterial fouling was greater during the late Z4 stage in the larvae reared at 8°C compared to those reared at 11°C, which was likely due to the longer intermolt duration at the lower temperature allowing more time for bacterial accumulation on the exoskeleton. We found that red king crab larvae can be cultured in a substantially shorter time period without compromising survival or health by increasing rearing temperature from 8 to 11°C.