Figure 4

Figure 4

Changes in muscle ultrastructure and mitochondria. (A) Electron micrograph of a longitudinal section of the skeletal muscle. (a) 2-month-old fish showed myofibrils (Mf), isotropic bands (I), anisotropic bands and (A) sarcomeres between each two successive Z-Line (Z). (b) sarcoplasmic reticulum (SR), mitochondria (M) and an area of ill-developed myofibrils was detected (black asterisk). (c) the triad region, formed by transverse tubules (T and white arrow) and terminal cisterns (C), was evident. The nucleus (N) was peripherally located under the sarcolemma (black arrow). (d) At an age of 10 months old, we observed normal myofibrils (Mf), sarcoplasmic reticulum (SR), and mitochondria (M), with the presence of vacuolated mitochondria (white arrow). (e) It was showed vacuoles (V), glycogen droplets (g), and (f) peripherally positioned nucleus (N) under the sarcolemma (black arrow), and interstitial tissues (In). (g) 30-month-old fishes presented normal myofibrils (Mf), swollen sarcoplasmic reticulum (SR), and hypertrophied mitochondria (M), (h) with the presence of indistinct mitochondrial cristae (white asterisk), vacuoles (V), and (i) shrinkage of nucleus (N). (j–l) The 60-month-old group showed disorganized myofibrils (Mf) and mitochondria (M) with the presence of damaged ones and others with damaged and/or disorganized cristae as well as vacuoles (V). Scale bar = 1 μm. (B) Sarcomere length decreased with age. (C) The number of IFMs and (D) their CSA decreased significantly at 60 months of age. (E) The number of SSMs increased in the 30-month group. (F) No difference was found in the CSA of SSM. (G) Band A length increased in 60-month-old fish, (H) as did the H band. (I) The length of the I band decreased in the 60-month group. (J) Mitochondrial damage increased sharply in the older group. Data are presented as mean ± SEM (n = 4 animals/group). * p < 0.05 vs. 2 mo; ** p < 0.01 vs. 2 mo; *** p < 0.001 vs. 2 mo; # p < 0.05 vs. 10 mo; ## p < 0.01 vs. 10 mo; ### p < 0.001 vs. 10 mo; $$ p < 0.01 vs. 30 mo; $$$ p < 0.001 vs. 30 mo. One-way ANOVA with a Tukey’s post hoc test.