Specific Dynamic Action and Growth in Larval Atlantic Cod, \u3cem\u3eGadus morhua\u3c/em\u3e, in Relation to Feeding and Temperature

During the larval stage, marine fish experience rapid growth and development. Atlantic cod, Gadus morhua, are around 4 mm in length upon hatching and may grow as much as 10% of their body weight day-1 within the first few weeks after hatching. The types of studies conducted on marine larvae are limited because larvae are very fragile and may be difficult to work with. Little data exists on the metabolism of early larval growth and most of that data has been collected using respirometry on groups of larvae. This study was one of the first to record changes in metabolic heat output of individual larva as a function of feeding and temperature using a microcalorimeter. This study used microcalorimetry to identify specific dynamic action (SDA) which represents the cost of feeding, digestion, and growth in larval Atlantic cod. Growth rates for two populations [Maine (CCAR) and New Brunswick (St. Andrews)] of Atlantic cod were measured and ranged from 0.033mg day-1 to 0.039mg day-1. Growth rates were not found to be significantly different between populations. Using a Thermometric© LKB 2277 microcalorimeter (TAM) the total (aerobic + anaerobic) metabolic heat output of larval cod from 1 to 41 days post hatch was determined under two different feeding conditions (unfed and fed) and two different temperatures (8°C and 12°C). Two cod of the same age (days post hatch) were placed concurrently into the TAM in two separate channels. One cod larva has been starved for 12 hours prior to the experiments (unfed) while the other larva was fed for 30 minutes prior to the beginning of the experiment (fed). The larvae were placed in the TAM and then the metabolic heat output was recorded for 12 hours. Measurements from the TAM showed that unfed larvae had a lower metabolic heat output than the fed larvae and both unfed and fed larvae showed increases in metabolic heat output over the course of the experiment and with age. Larvae reared at 8°C grew well throughout the experiment while the larvae reared at 12°C did not grow throughout the experiment and all were dead by 11 days post hatch