ACCUMULATION OF FLUORESCENT AGE PIGMENTS IN A LABORATORY POPULATION OF ANTARCTIC KRILL EUPHAUSIA-SUPERBA DANA

Age-class separation by morphometric means has proved difficult for Antarctic krill Euphausia superba because the size of the animals does not necessarily relate to their age in any predictable fashion. The measurement of temporal increases in quantities of fluorescent age-pigments has been suggested as a method which obviates the problems associated with size-related measures of age. In this study, a laboratory population of Antarctic krill exhibited a clear increase in the mean amount of fluorescent age-pigment per animal over a period of 1 yr. At the same time the mean weight of the animalsin the population decreased markedly-body shrinkage. Analyses of fluorescence- and weight-frequency plots from samples taken a year apart demonstrated that the fluorescence technique could successfully discriminate the two year groups and determine their correct temporal sequence whereas the weight frequency analysis was less successful at discriminating the two peaks and placed them in an incorrect temporal sequence. On the basis of these results it is suggested that age-pigment fluorescence may now be a useful tool in the analysis of age-structure in populations of Antarctic krill.