Mechanochemical properties of ordinary and dark muscle myosins from seawater fish

Myosin was isolated from two types of muscle, ordinary and dark muscles, of three species of fish living in sea water. The compositions of light chains were visualized by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the mechanochemical activity was examined by in vitro motility and ATPase assays. Ordinary muscle myosin of either species had three species of light chain, whereas dark muscle myosin had another two species of light chain judged by SDS-PAGE. Sliding velocity of ordinary muscle myosin was in the range of 4.92–6.89 μm/S, whereas that of dark muscle myosin was in the range of 3.07–4.25 μm/s. Therefore, ordinary muscle myosin showed 1.26–1.95 times higher sliding velocity than dark muscle myosin in either species. The ratios of V_max of actin-activated Mg²⁺-ATPase activity of ordinary to dark muscle myosins were correlated quite well to the ratios of sliding velocity. Activity of ordinary muscle myosin was comparable to that of mammalian fast muscle myosin, but that of dark muscle myosin was twice of that of mammalian slow muscle myosin. These results may reflect the essential role of fish dark muscle myosin always used in slow cruising.     

Site of acid-base relevant ion transfer in the gills of rainbow trout (Oncorhynchus mykiss) exposed to environmental hypercapnia

In order to delineate the contribution of primary vs. secondary circulatory circuits in the gill for acid-base and ionic regulation, the flow and composition of the fluids in the central venous sinus (CVS) and the systemic circuit of rainbow trout were studied by application of a previously developed microcannulation technique during normocapnic and hypercapnic conditions. The average haematocrit (Hct) of blood from dorsal aorta (DA) and sinus venosus (SV) ranged from 20.1 to 26.7%, whereas average Hct in the fluid from the branchial vein (BV), representing drainage from the central venous sinus (CVS), was in the range of 4.2 to 7.0%. Under normocapnic conditions, the largest fraction of cardiac output, 92.9%, was directed through the systemic vascular circuit, whereas the CVS circuit was perfused with 7.1 % of cardiac output. Hypercapnia did not significantly affect the blood flow distribution between the two circuits. The pattern of acid-base regulation in dorsal aortic blood reflected the characteristic response of fish exposed to environmental hypercapnia. Upon initiation of environmental hypercapnia (2% CO₂), plasma P_{CO 2} was elevated in all three flow compartments (CVS, DA, SV), inducing an extracellular respiratory acidosis of about 0.4 pH units. pH and [HCO₃ ^-] values in the DA were consistently lower, than those for both CVS and SV sites throughout the hypercapnic period. During the 8h of exposure plasma bicarbonate concentration was elevated by about 12 mM, complemented by a fall in extracellular [Cl^-] of about 10 mM in all three compartments. The amount of HCO₃ ^- gained at the CVS site during 8h of hypercapnia (3.3 mmol · kg^-1) exceeds the amount accumulated in the extracellular space (2.1 mmol·kg^-1), suggesting the CVS as the main site of ionic acid-base regulation in trout.     

Estimation of flow in a rearing tank of marine fish larvae by simplified numerical computation—a case of two-dimensional flow

Marine fish larvae are fragile against physical stress. However, few studies have been conducted to evaluate the flow field in a rearing tank, which is assumed to provide a high degree of physical stress to marine fish larvae. The flow field in a rearing tank (volume of 1 m³) is generated by aerators, which are commonly used to provide oxygen.

This paper is a report on the estimation of stationary flow in the rearing tank of marine fish larvae. The larvae are seven band grouper larvae of Epinephelus septemfasciatus, which have a very low survival rate immediately after the hatching of eggs. The experiments of rearing of seven band grouper larvae were carried out using rearing tanks with four aeration rates (1000, 200, 50 ml/min, and no aeration). The effects of aeration on the survival and floating death of seven band grouper larvae were examined. The experiments confirmed that the mass mortality of seven band grouper larvae depends on the flow rate in the rearing tank. Aeration at 200 ml/min resulted in the highest survival and growth rates of grouper larvae.

Larvae-rearing experiments provided evidence that the flow rates of the rearing tanks are very important design aspects of rearing tanks. The estimation of flow in a rearing tank for an aerating rate of 200 ml/min was carried out by numerical calculation. The computation was simplified by a two-dimensional flow based on experimental results. The calculated flow in the rearing tank was compared with the experimental one. The calculation of the stationary flow in the rearing tank showed good qualitative and quantitative agreement with the experimental results. The numerical estimation of the flow in a rearing tank of marine fish larvae was confirmed to be effective and satisfactory for the design of a tank that would provide optimum performance.     

Patterns of stable carbon and nitrogen isotopes in the baleen of common minke whale Balaenoptera acutorostrata from the western North Pacific

ABSTRACT:   Stable carbon and nitrogen isotope ratios were determined in the baleen plates of 17 common minke whales Balaenoptera acutorostrata from the north-western Pacific Ocean off Japan, as well as prey species (krill Euphausia pacifica , Japanese anchovy Engraulis japonicus and Pacific saury Cololabis saira ) collected in the stomach contents, to investigate the trophic relationship between the minke whales and their prey. A few δ¹⁵N-depleted peaks occurred along the length of baleen plates for 10 males irrespective of stomach content (anchovies and sauries). Similar δ¹⁵N-depleted peaks were also found for one female and two immature individuals. It was likely that these δ¹⁵N-depleted peaks formed in early summer. The stable nitrogen isotope ratio (δ¹⁵N) values in Pacific saury (9.3 ± 1.4‰) did not differ significantly from that in Japanese anchovy (8.8 ± 0.9‰). In contrast, δ¹⁵N in krill (7.2 ± 0.5‰ in July and 8.0 ± 0.2‰ in September) were significantly lower than in the Pacific saury. Thus, these peaks may reflect the dietary change from krill to fishes in the feeding migration of the whales. Growth rate of the baleen plate was estimated to be 129 mm/y, and it appeared that a dietary record of about 1.4 years remained in the baleen plate. For two immature whales, the maximum value of δ¹⁵N occurred at the tip of baleen. This δ¹⁵N enrichment may possibly be useful for discriminating weanlings and older whales.     

Effect of taurine supplemented practical diet on growth performance and taurine contents in whole body and tissues of juvenile Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

ABSTRACT:   The effect of dietary taurine on juvenile Japanese flounder was determined by feeding three taurine-supplemented experimental diets (TAU) and a commercial diet (CD) to evaluate a practical diet for juvenile Japanese flounder. Juvenile Japanese flounder were reared on the three experimental diets supplemented with taurine at 0, 0.5, 1.0% and CD. These diets were fed to juvenile Japanese flounder of an initial mean body weight of 0.2 g for 6 weeks at 20°C and the taurine contents of the whole body and tissues were analyzed. The final average body weight of juvenile Japanese flounder fed the 1.0% TAU was significantly higher than that of the other groups. Taurine contents in the whole body and tissues increased with the increase in dietary taurine level. These results indicate that juvenile Japanese flounder require at least 15 mg/g taurine in the diet, even though a combined mix of fish, krill and squid meal was the main protein source in the experimental diets.     

Lectin binding patterns in the olfactory bulb of mallard ducks (Anas platyrhynchos)

We histologically examined lectin binding patterns in the olfactory bulb of mallard ducks (Anas platyrhynchos) using 21 biotinylated lectins. Positive staining for the N‐acetylglucosamine‐specific lectins (Bandeiraea simplicifolia II, Datura stramonium, Lycopersicon esculentum, Solanum tuberosum, Triticum vulgare), galactose or N‐acetylgalactosamine‐specific lectins (Artocarpus intergrifolia, Phaseolus vulgaris erythroagglutinin, Phaseolus vulgaris leucoagglutinin, Ricus communis) and the mannose‐specific lectins (Lens culinaris and Pisum sativum) was observed in the olfactory nerve and glomerular layers. Canavalia ensiformis staining showed a similar pattern to that obtained with the lectins and there was also faint staining in the mitral cells. Olfactory nerve axons terminate in the glomeruli, where they make excitatory synapses with the dendrites of mitral cells. This finding indicates that glycoconjugates that bind Canavalia ensiformis play an important role in formation of glomeruli. No positive staining for the other lectins was seen in the olfactory bulb. Based on these results, we conclude that cell surface sugar moieties of the olfactory bulb in mallard ducks express N‐acetylglucosamine and mannose residues rather than N‐acetylgalactosamine residues. The carbohydrate composition of mallard duck olfactory bulb differed from that of other vertebrates found in previous studies.