The use of scale increment as a means of indicating fish growth and growth impairment

Growth impairments were studied for three juvenile fish species: the red drum (Sciaenops ocellatus), the orange-spotted grouper (Epinephelus coioides) and the marine medaka (Oryzia melastigma). Fish were subjected to long-term (i) food deprivation, (ii) exposure to benzo[a]pyrene, (iii) hypoxia, respectively. Fish growth (fork length and body weight) and scale increments (circulus number and radius length) were measured. Results of Pearson correlation analysis showed a significant positive correlation between scale increment and growth for the red drum (fast growing) and the marine medaka (small sized) (r = 0.741-0.882, p <0.001). For the slow growing orange-spotted grouper, a significant correlation was found only between body weight and circulus number (r = 0.406, p <0.05). Overall, scale circulus number is more consistently linked to fish growth than that of radius length. Importantly, our findings demonstrate that daily circulus deposition on scales of fast-growing red drum is feasible to indicate daily growth of the fish. Moreover, scale increment exhibited the strongest correlation with fish growth as compared to that of serum T₃ level and muscle RNA:DNA ratio. Our data support the use of scale increment as a means of indicating fish growth and growth impairment, particularly for the fast growing fish. © 2007 Elsevier B.V. All rights reserved.