Capillary distribution and metabolic histochemistry of the lateral propulsive musculature of pelagic teleost fish

Effect of Propolis on the Fish Muscular Development and Histomorphometrical Characteristics

The aim of our study was to evaluate the effect of propolis on mortality of fish eggs due to mycosis, to study its efficacy on the fish growth rate and to analyze the histochemical and ultrastructural characteristics of muscle fibres. We evaluated the muscular development of fish in two different experimental conditions: traditional feeding and feeding with addition of propolis (groups A and B, respectively). The study was carried out on two species of teleosts bred in Italy, Oncorhynchus mykiss (rainbow trout) and Salmo trutta (brown trout). The use of propolis reduced mortality of fish eggs. The muscles were stained for myosin ATPase and succinic dehydrogenase to evaluate fibre type. The area, maximum and minimum diameter for each fibre type in relation to the body length were measured. The animals fed propolis showed a more rapid muscular growth compared to control fed the standard diet. Fibres were larger in the Salmo trutta than in the Oncorhynchus mykiss in both groups. In fish of A group, myotomal muscle, the presence of giant fibres and index of environmental stress was noticed. This type of study is valuable in order to extend the use of propolis as an antifungal agent and a natural product that can improve fish farming.

Partition of aerobic and anaerobic swimming costs related to gait transitions in a labriform swimmer

Members of the family Embiotocidae exhibit a distinct gait transition from exclusively pectoral fin oscillation to combined pectoral and caudal fin propulsion with increasing swimming speed. The pectoral–caudal gait transition occurs at a threshold speed termed Up–c. The objective of this study was to partition aerobic and anaerobic swimming costs at speeds below and above the Up–c in the striped surfperch Embiotoca lateralis using swimming respirometry and video analysis to test the hypothesis that the gait transition marks the switch from aerobic to anaerobic power output. Exercise oxygen consumption rate was measured at 1.4, 1.9 and 2.3 L s–1. The presence and magnitude of excess post-exercise oxygen consumption (EPOC) were evaluated after each swimming speed. The data demonstrated that 1.4 L s–1 was below the Up–c, whereas 1.9 and 2.3 L s–1 were above the Up–c. These last two swimming speeds included caudal fin propulsion in a mostly steady and unsteady (burst-assisted) mode, respectively. There was no evidence of EPOC after swimming at 1.4 and 1.9 L s–1, indicating that the pectoral–caudal gait transition was not a threshold for anaerobic metabolism. At 2.3 L s–1, E. lateralis switched to an unsteady burst and flap gait. This swimming speed resulted in EPOC, suggesting that anaerobic metabolism constituted 25% of the total costs. Burst activity correlated positively with the magnitude of the EPOC. Collectively, these data indicate that steady axial propulsion does not lead to EPOC whereas transition to burst-assisted swimming above Up–c is associated with anaerobic metabolism in this labriform swimmer.

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

Histochemical and ultrastructural studies were performed on lateral musculature from individual female weakfish (Cynoscion striatus Cuvier). Based upon SDH, PhR, Sudan and myosin-ATPase determinations, different kinds of red, pink and white fibres were discerned at the anterior, medium and posterior regions. Levels of glycolytic activity increased from red to white fibres, being intermediate in the pink ones. Contrarily, oxidative activity decreased from red to pink and white fibres. Histochemical stain showed a complex distribution of fibre types in each layer. A considerable variation in size and distribution was also found among fibres.

Effects of sustained swimming on rainbow trout muscle structure, blood oxygen transport, and lactate dehydrogenase isozymes: evidence for increased aerobic capacity of white muscle

Groups of rainbow trout (Salmo gairdneri, Richardson) were continuously swum at 20 cm s-1 (1.0 body lengths s-1) for 0, 3, 30, and 200 days. No significant changes in fish condition factor, combined red and white muscle mass, muscle fibre size or fibre size distribution were observed. After 200 days of swimming there was a significant 2.2 fold increase in red muscle mass. Number of capillaries per red muscle fibre increased significantly in each group by a maximum of 27% after 200 days exercise. Number of capillaries per white muscle fibre increased significantly by 95% after 200 days exercise. Blood lactate, haemoglobin (Hb) concentration haematocrit, erythrocyte adenosine triphosphate, and whole blood oxygen affinity P50 were unchanged by swimming. After 30 and 200 days swimming there was a shift in expression of white muscle lactate dehydrogenase (LDH) isozymes from LDH-A to LDH-B. Within the duplicated LDH-B isozyme complex, there was a shift in expression from LDH-B to LDH-B' subunits. These results suggest that sustained swimming at 1(-1) bl s-1 increased the aerobic capacity of red and particularly white (fast) muscle of rainbow trout but did not alter the gas transport characteristics of the blood.

Skeletal muscle capillary supply in a fish that lacks respiratory pigments

The relationship between capillary density and mitochondrial volume density has been investigated for the slow trunk muscle of the haemoglobinless 'Icefish', Chaenocephalus aceratus Lönnberg. In general, for teleost slow muscles capillary densities, NA(c,f), are positively correlated with mitochondrial volume densities, Vv(mit,f). However, the capillary density for the slow trunk muscle of the Icefish is low (544 +/- 24 capillaries/mm2) when compared with teleosts of similar mitochondrial volume densities (0.34 +/- 0.01). For example, for slow muscle fibres in Saithe (Pollachius virens) Vv(mit,f) is 0.35 +/- 0.02 but the capillary density is 4507 capillaries/mm2. Estimates of capillary surface and volume densities for the Icefish (198 and 0.035 cm-1, respectively) are in the range reported in the literature for other teleost species. Thus, for C. aceratus NA(c,f) provides a relatively poor index of the functional properties of the peripheral exchange vessels. Mean capillary cross-sectional area for C. aceratus (64 +/- 7 micron2) was two to three times greater than that found in most teleost species. The low peripheral resistance reported for the Icefish, C. aceratus is therefore the result of the presence of large bore capillaries, the resulting high flow rates also allowing the maintenance of favourably high capillary - tissue PO2 gradients.

Morphometric study on vascularization in the tail musculature of the anuran tadpole by scanning electron microscopy: I. Prometamorphic stage

Vascularization in the tail musculature, which contains red and white muscle fibers, of the prometamorphic anuran tadpole was analyzed quantitatively by scanning electron microscopy (SEM). The sample was fixed in glutaraldehyde and osmium tetroxide; this was followed by freeze-fracturing in liquid nitrogen. As good ultrastructural preservation and reliable identification of capillaries were given by this technique, various morphometric parameters, cross-sectional capillary area in particular, could be measured exactly. In red muscle fiber that had a small cross-sectional area (2,060.1 micron2), high capillary density (1,283.5 capillaries/mm2) and a large cross-sectional capillary area (96.4 micron2) was found. Although white fiber (9,327.2 micron2) was 4.6 times greater than red fiber in cross-sectional fiber area, capillary density (95.8 capillaries/mm2) and cross-sectional capillary area (29.5 micron2) were 13.4 times and 3.3 times smaller than those of red fiber, respectively. From these morphometric values the following parameters were evaluated; (1) capillary/muscle fiber number ratio of red muscle fiber (2.64) was 3.0 times greater than that of white fiber (0.89); and (2) total cross-sectional capillary area per cross-sectional area of one muscle fiber was 44.0 times greater for red fiber (1,235.4 micron2)/10(4) micron2) than for white fiber (28.1 micron2)/10(4) micron2). Comparison of the latter parameter between the different fiber types may reflect the differences of real blood supply to them; i.e., red fiber was supplied a 44.0-times richer blood flow than white fiber. Advantages of morphometric study by SEM, and the relationship between obtained parameters for vascularization and blood supply to the different muscle fiber types, are discussed.

Quantitative analyses of ultrastructure and vascularization of the slow muscle fibres of the anchovy

A quantitative study has been made of the ultrastructure and vascularization of slow fibres in the lateral muscles of the European anchovy (Engraulis encrasicolus). Mitochondria and myofibrils occupy 45.5 and 44.3% of total fibre volume respectively. More than 95% of all myofibrils are adjacent to mitochondria. A total of 51% of the sarcolemma is in direct contact with capillaries with a mean of 12.9 capillaries per fibre. In transverse sections anchovy slow fibres are considerably flattened (long to short axis 12:1) such that the surface to volume ratio is more than twice that of a cylindrical fibre of the same area (1115 micron2). The capillary surface required to supply 1 micron3 of mitochondria is 0.18 micron2 and the maximum distance between any capillary and mitochondrion 8 microns. T-system and sarcoplasmic reticulum occupy 0.43 and 2.7% of fibre volume respectively. Adaptations for increasing the capacity of skeletal muscle for aerobic work are discussed.