Comparison of lipid, otolith and morphometric condition indices of pelagic juvenile cod Gadus morhua from the Canadian Atlantic

Body condition indices were assessed for pelagic juvenile cod (14 to 31 mm standard length, SL) over 2 cruises in spring 1987 in Canadian Atlantic waters on the southern Scotian Shelf. Three different indices determined from the residuals of univariate regressions were (1) triacylglycerol (TAG) content on standard length (SL), (2) dry body weight on SL, and (3) back-calculated change in SL from the peripheral 14 daily growth increments of the otolith on SL; hereafter referred to as TAGSL, DWTSL, and OTOSL respectively. Correlations between indices declined from TAGSL:DITSL (0.69, 0.64, cruises 87-1 and 87-2 respectively), to TAGSL:OTOSL (0.38. -0.05), to DWTSL:OTOSL (0.05, 0.03), a surprisingly low correlation considering that the indices were derived from the same individual. This pattern was also demonstrated by a principal component analysis (PCA), showing that after the first (size) component, otolith-based growth alone loaded on PC 2, then TAG contrasted with SL loaded on PC 3, and dry body weight showed the highest correlation with the starvation-independent SL. Supplementary analyses from 4 other cruises during 1985 and 1986 confirmed the weak correlation between DWTSL, OTOSL and other morphometric measures. All indlces were positively correlated with zooplankton biomass, but of the 16 separate cruise by index comparisons, only 6 were significantly correlated with zooplankton, of which 3 were the OTOSL. The rapld somatic/otollth growth of pelagic juvenile cod may respond rapidly to prey abundance, and rapid growth may preclude accumulation of Lipids (TAG), indicating that the utility of a con&tion lndex will depend on the species and life stage examined. Indices of recent otolith growth appear good measures of pelagic juvenile cod condition.