Effects of food consumption and temperature on growth rate and biochemical-based indicators of growth in early juvenile Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus

Abstract

The relationship between the somatic growth rate (G) and feeding level (unfed, intermediate, and maximum rations) of age-0 juvenile cod Gadus morhua and haddock Melanogrammus aeglefinus was quantified at different temperatures. Laboratory trials were conducted using 2 size-classes of cod (3.6 to 5.6 cm standard length [SL], and 8.1 to 12.4 cm SL) at 5, 8, 12, and 15°C, and 1 size-class of haddock (6.0 to 9.6 cm SL) at 8 and 12°C. The shape of the growth-feeding relationship was well described by a 3-parameter asymptotic function for cod and by a linear function for haddock (R2 range = 0.837 to 0.966). The growth rate and scope for growth were maximum at 12°C, whereas growth efficiency was greatest (26.0 to 32.2%) at temperatures between 5 and 8°C. Juvenile cod held at 15°C exhibited reduced rates and efficiencies of somatic growth compared to fish at other temperatures. Biochemical-based growth indicators for age-0 juveniles were calibrated from measurements of the amounts of RNA, DNA, and protein in white muscle samples. A multiple linear regression using RNA:DNA and temperature as independent variables explained a significant portion of the variability observed in G of juvenile cod (R2 = 0.716) and haddock (R2 = 0.637). This relationship may be useful in estimating recent growth of age-0 juvenile cod and haddock in the field.