Characterization of lateral musculature in the striped weakfish (Cynoscion striatus Cuvier)

Morphology of the claw closer muscle in two estuarine crab species (Crustacea, Varunidae): an ultrastructural study

We analyzed the ultrastructural features of the claw closer muscles in two estuarine crabs, Cyrtograpsus angulatus and Neohelice granulata, by transmission electron microscopy. Adult male crabs at intermolt stage were collected in the Mar Chiquita Coastal Lagoon (Buenos Aires, Argentina). The muscle fibers of both species showed evident striations, peripheral and intermyofibrillar nuclei, clefts in continuity with T and Z tubules, sarcoplasmic reticulum and T tubules forming dyads and triads usually located between the A and I bands, and mitochondria located mainly beneath the sarcolemma. Glycogen was observed as diffuse, small particles among myofilaments. The claw closer muscle of C. angulatus exhibited two fiber types: one with relatively fast-contracting fibers (shorter sarcomeres, myofilaments with an ordered arrangement, lineal Z discs, a well-developed sarcotubular system) and fatigue-resistant (numerous large mitochondria); and the other type, with slower-contracting fibers (longer sarcomeres, less orderly arranged myofilaments, wavy Z discs, a less developed sarcotubular system) and less resistant to fatigue (lower mitochondrial density). N. granulata showed only the slow, less resistant to fatigue type. The fibers less resistant to fatigue and more slowly contracting would presumably be used primarily for displays and agonistic interactions, whereas fast fibers with abundant mitochondria would be associated with continuous movements during feeding and grooming.

Pectoral fins of Micropogonias furnieri: a histochemical and ultrastructural study

The myotomal fibres of the pectoral fins of white croaker (Micropogonias furnieri) have been studied using histochemical techniques and transmission electron microscopy (TEM). Succinic dehydrogenase (SDH) for mitochondria, periodic acid Schiff (PAS) for glycogen, Sudan Black for lipids and myosin-adenosintriphosphatase (mATPase) pre-incubated at alkaline and acid pHs were used to visualize the contraction velocity. Three zones were determined: superficial (SZ), medium (MZ) and deep (DZ). Staining for SDH, PAS and Sudan Black was positive only in the SZ. The level of alkaline mATPase was the highest in fibres from the DZ, intermediate in the MZ and low in the SZ; at an acid pH, the reverse was obtained. Fibres from the SZ were small with large quantities of subsarcolemmal mitochondria, scarce intermyofibrilar mitochondria and a well-developed sarcoplasmic reticulum; the myofibrils displayed a polygonal distribution along the entire length of the fibre. Fibres in the MZ were larger than those in the SZ, the myofibrils were densely packed, mitochondria prevailed under the sarcolemma and the sarcoplasmic reticulum was not abundant. Fibres from the DZ were the largest, with ribbon-shaped myofibrils and scarce mitochondria. The intercellular space was abundant and nervous endings were frequently observed.

Characterization of the swimming muscle of the anchovy Engraulis anchoita (Hubbs and Martini 1935)

The lateral muscle characteristics of individual female anchovies (Engraulis anchoita) were studied by histochemical and ultrastructural techniques. Red, pink and white fibres were discerned on the basis of the activity of the metabolic enzymes succinic dehydrogenase, phosphorylase and myofibrilar ATPase, and the usage of Sudan and periodic-acid Schiff staining techniques. Red fibres were located at the surface, white fibres deep inside and pink fibres in between. The red fibres appeared flattened or ribbon-shaped in transverse section and they were located in rows separated by myosepta of connective tissue. The red and pink fibres were multi-innervated whereas the white fibres were terminally innervated. The relative proportion of the red muscle increased toward the caudal region, the white muscle diminished toward that region, whereas the proportion of pink muscle did not vary according to region, being scarce throughout. The distribution of capillaries was also investigated, and as a result, the vascular supply proved to be scarce in both white and pink muscle.

Lateral musculature in the whitemouth croaker (Micropogonias furnieri): its characterization with respect to different gonadal conditions

Histochemical and ultrastructural studies were performed on the lateral musculature from individual female whitemouth croaker, Micropogonias furnieri, at the anterior, medium and posterior regions. Based upon histochemical myosin-ATPase (m-ATPase) determination, diverse types of red, pink and white fibres were discerned. Red muscle had abundant mitochondria and stained intensely for aerobic enzymes, white muscle scarcely stained for the same enzymes and pink muscle responded in an intermediate manner. Both white and pink muscle had few mitochondria. The relative proportion of red muscle increased towards the caudal region; pink muscle diminished towards this region and white muscle modified its proportion only in the anterior region. m-ATPase activity showed differences in relation to the gonadal condition along the body, particularly in the white fibres at the anterior and medium regions.