Effects of variable ration levels on direct and
indirect measures of growth in juvenile red drum (Sciaenops ocellatus)
M.W.
Johnson, J.R. Rooker, D.M. Gatlin III, G.J. Holt-2002
Journal
of Experimental Marine Biology and Ecology, 274(2): 141-157
Abstract:
Relationships
between somatic growth (length and weight) and two indirect measures of
growth (otolith growth, RNA/DNA ratio) were assessed for red drum (Sciaenops
ocellatus) under different feeding rations [0%, 2.5%, 5%, 10%, 15%, and
20% body weight (BW)/day] for 30 days. Representative samples from each
ration level were taken in 10-day intervals between Day 0 and Day 30 for
evaluation of direct and indirect growth measures. Positive correlations
were observed between ration levels, somatic growth, and otolith growth.
Statistical differences in weight and length of red drum were observed among
ration levels by Days 10 and 20, respectively. Statistical differences for
measures of otolith growth among ration levels were evident by Days 20 and
30. In addition, RNA/DNA ratios showed clear separation between fish that
were starved and fish that were fed but demonstrated minimal separation
among ration levels. Overall, the combination of a measure of somatic growth
(weight) and a measure of otolith growth (otolith weight) resulted in the
most statistical separation among ration levels. Findings from this study
suggest that somatic growth, otolith growth and RNA/DNA ratios are suitable
measures of relative growth of red drum; however, due to differences in
sensitivity, caution must be exercised when using indirect growth (otolith
growth, RNA/DNA ratios) measures to estimate recent growth.
(Department
of Wildlife and Fisheries Sciences, Texas A&M University, 210 Nagle
Hall, College Station, TX 77802, USA, Tel.: +1-251-861-7551; fax:
+1-251-861-7540, e-mail: mjohnson@disl.org)