THEILACKER: MORTALITY OF SEA-CAUGHT JACK MACKEREL 



jack mackerel collected near islands and banks (Fig. 

 10) whereas healthy jack mackerel collected offshore 

 showed moderate to little storage (Fig. 9). 



At the other end of the grading scale, the shrunken 

 livers of jack mackerel considered to be starving con- 

 tained darkly stained hepatocytes composed of even- 

 ly stained cytoplasm with indistinct, irregular nu- 

 clei. 



Musculature 



Healthy muscle tissue in jack mackerel had the 

 following characteristics: few spaces between the 

 muscle fibers; distinct and parallel, striated myo- 

 fibrils; and abundant, basophilic and nucleated intra- 



muscular tissue (Fig. 9). Nourishment was con- 

 sidered inadequate in fish exhibiting separated (Figs. 

 11, 14) and hyaline muscle fibers (Fig. 13) and a 

 reduction (Figs. 11, 14) or absence (Fig. 13) of intra- 

 muscular tissua In some sea-caught jack mackerel, 

 muscle fibers were wavy (Fig. 8). Presence of wavy 

 muscle fibers in wild fish was considered abnormal 

 because it was always associated with the poor con- 

 dition in the other diagnostic tissues, but this charac- 

 teristic was not used in classification. In starved 

 laboratory fish, nonparallel fibers were reported 

 (Theilacker 1978, 1981), but the wavy pattern was 

 unusual. There were fish with intermediate spaces 

 between muscle fibers that, according to the scores 

 of the other diagnostic tissues, appeared healthy. The 



Figure 11.— Trachurus symmetricus larva graded recovering. Prominent separations between midgut and hindgut epithelial cells, slight 

 muscle fiber separation and intermediate intermuscular tissue containing distinct nuclei. Bar = 47 \im. HG = hindgut, IM = inter- 

 muscular tissue, M = muscle, MG = midgut, N = notochord. 



Figure 12— Healthy Trachurus symmetricus larva showing luminal vacuoles in the midgut. This histological characteristic was not 

 graded. Bar = 47 ^m. M = muscle, MG = midgut. 



Figure 13.— -Trachurus symmetricus larva graded dying. No intermuscular tissue; hyaline muscle fibers; total degeneration of midgut 

 mucosa. Bar = 34 ^m. HG = hindgut, M = muscle, MG = midgut. 



Figure 14— Recovering Trachurus symmetricus larva showing slight muscle fiber separation and slight reduction of intermuscular 

 tissue Bar = 47 \im. HG = hindgut, IM = intermuscular tissue, M = muscle, MG = midgut, N = notochord. 



