Fig. 4. Change in dry relative ventricular masses for compact (lower portion) and spongy (upper) myocardium in warm-acclimated rainbow trout induced by four phenylhydrazine hydrochloride injections at weeks 0, 2, 4 and 6 (hatched columns) compared with sham-injected control fish receiving saline (open columns) and followed by a recovery period to week 12. Values are means ± s.e.m., N=6. The horizontal lines denote mean values for the pre-treatment (day 0) controls (the dotted lines represent ± s.e.m.). ⁺Significant difference (P<0.05) from the pre-treatment control value at week 0, as detected by ANOVA and Dunnett's test. ^*Significant difference (P<0.05) between the dry relative myocardial masses (compact, spongy and total) of time-matched PHZ-treated and sham-injected groups, as determined by Student's t-test statistic (P<0.05).