Age, Growth and Maximum Size of Antarctic Notothenioid Fish - Revisited
37
polar marine invertebrates) suggests that although low temperature due to
its rate-depressing effect on physiological systems is likely to impose
some general constraint on growth, it is seasonal food availability and not
temperature that normally limits growth rate. The evidence from adult fish
appeared to be more equivocal.
Both, otoliths and scales in most nototheniids and channichthyids
investigated exhibited a clear seasonal signal [15]. Although our analysis
showed that information on seasonality in feeding is not unequivocal,
there is sufficient evidence to suggest that seasonal cycles, such as
changes in the availability of food and seasonal variation in its energy
content [9,37] and the low feeding intensity during the reproductive
season [1] may preclude year round growth for many species with the
result that under favorable conditions growth can be relatively fast. Hence,
ecological constraints are likely to affect growth rate during the year much
more than temperature per se and may also largely account for differences
in growth performance between species. Our observations are
corroborated by findings that differences in activity, metabolic rate,
perception of stimuli or behavior among Antarctic notothenioids appear to
be much more influenced by the ecological niche a fish species inhabits
than by temperature per se [38].
Growth is almost certainly impaired after the fish become sexually
mature due to the significant energy costs attendant on reproductive effort.
Most Antarctic fish do not start to reproduce before they reach 55-80% of
their maximum observed length. Postponing maturity until after achieving
a size large enough to exploit abundant food resources, such as
amphipods, krill and other euphausids, seems to be one plausible reason
for delayed maturity.
We consider that there is an increasing body of evidence now available
which does not support the view that Antarctic fish grow slowly.
However, age and growth studies should remain an important topic for
Antarctic fish research in the future. We suggest that studies on age and
growth should focus on
• the validation of ageing, incorporating different techniques, such as
the analysis of length compositions of juvenile fish from scientific
surveys and the analysis of daily ring structures in otoliths and
elemental ratios in microstructure which provide not only powerful
tools to validate age but additionally provide information to the
individual ecological and physiological past;
• an extension of age and growth estimates to artedidraconids and
bathydraconids;
37
polar marine invertebrates) suggests that although low temperature due to
its rate-depressing effect on physiological systems is likely to impose
some general constraint on growth, it is seasonal food availability and not
temperature that normally limits growth rate. The evidence from adult fish
appeared to be more equivocal.
Both, otoliths and scales in most nototheniids and channichthyids
investigated exhibited a clear seasonal signal [15]. Although our analysis
showed that information on seasonality in feeding is not unequivocal,
there is sufficient evidence to suggest that seasonal cycles, such as
changes in the availability of food and seasonal variation in its energy
content [9,37] and the low feeding intensity during the reproductive
season [1] may preclude year round growth for many species with the
result that under favorable conditions growth can be relatively fast. Hence,
ecological constraints are likely to affect growth rate during the year much
more than temperature per se and may also largely account for differences
in growth performance between species. Our observations are
corroborated by findings that differences in activity, metabolic rate,
perception of stimuli or behavior among Antarctic notothenioids appear to
be much more influenced by the ecological niche a fish species inhabits
than by temperature per se [38].
Growth is almost certainly impaired after the fish become sexually
mature due to the significant energy costs attendant on reproductive effort.
Most Antarctic fish do not start to reproduce before they reach 55-80% of
their maximum observed length. Postponing maturity until after achieving
a size large enough to exploit abundant food resources, such as
amphipods, krill and other euphausids, seems to be one plausible reason
for delayed maturity.
We consider that there is an increasing body of evidence now available
which does not support the view that Antarctic fish grow slowly.
However, age and growth studies should remain an important topic for
Antarctic fish research in the future. We suggest that studies on age and
growth should focus on
• the validation of ageing, incorporating different techniques, such as
the analysis of length compositions of juvenile fish from scientific
surveys and the analysis of daily ring structures in otoliths and
elemental ratios in microstructure which provide not only powerful
tools to validate age but additionally provide information to the
individual ecological and physiological past;
• an extension of age and growth estimates to artedidraconids and
bathydraconids;