Effect of temperature and photoperiod on the growth of the embryonic dogfish, Scyliorhinus canicula

Photoperiod has no effect on the growth of embryonic dogfish. Conversely, developmental rates are highly susceptible to temperature variation. Embryos maintained at 16°C grew faster and ecloded earlier than those maintained at 10°C. Increased temperature had no effect on size at eclosion.     

Ventilatory mechanisms and the effect of hypoxia and temperature on the embryonic lesser spotted dogfish

Small, intermediate and large-sized embryos of the dogfish Scyliorhinus canicula utilize different ventilatory methods; small and intermediate embryos rely on body movement alone to stir either the jelly or sea water in the capsule, large embryos use conventional pharyngeal pumping to pump water through the case. The effects of environmental changes in O₂ tension (0.5–100% air saturation) and temperature (6–18°C) upon ventilatory mechanisms in the developing embryo in situ were studied using non-invasive ultrasonography. All three embryo classes increased ventilation rate with rising temperature: for small embryos, y=2.02x+3.295 ( P <0.01); for intermediate embryos, y=3.51x+0.395 ( P <0.01); and for large embryos, y=3.81x+9.39 ( P <0.01); where y=ventilatory frequency (tail beats min⁻¹ or pump cycles min⁻¹) and x=temperature (°C). Q ₁₀ (6–16°C)=5.0, 2.45, and 2.08 for small, intermediate and large embryos, respectively; corresponding Q ₁₀ (8–18°C) values were 2.09, 2.62, and 2.02. It is suggested that the extreme response of small embryos to 6°C is related to a different state of development in either chemoreceptors or muscle blocks. There was no significant change in ventilatory frequency induced by chronic (2 h) hypoxia. Dogfish embryos are oxyconformers at 8°C but oxyregulators at higher temperatures. Water flow through an eggcase occupied by a large embryo was studied also. Water enters the open eggcase of a large embryo, drawn in by the buccal/opercular pump of the respiring embryo, via holes at the posterior end of the eggcase. Expired water exits holes at the anterior end of the eggcase. The mean residence time for water in the case is 50 s at 8°C, giving a transit velocity of 1.36 mm s⁻¹.     

Endocardial pores in the sinus venosus and atrium of the dogfish

A scanning electron microscopy study showed the presence of large pores in the endocardium of the sinus venosus of the dogfish Scyliorhinus canicula. The pores were always found on large bundles which protruded into the cardiac lumen. The bundles were mainly constituted of granule-containing nerve fibres. The average diameter of the pores was 3.2 μm (range=1.5-5.0μm), and their density, was about 822 pores mm⁻². Endocardial pores were absent in other areas of the sinus venosus, but they were observed on the little bundles of granulated nerve fibres which were scattered throughout the atrium. The existence of large endocardial pores associated with bundles of granulated nerve fibres supports the hypothesis for the neuroendocrine nature of the elasmobranch sinus venosus wall.     

Effects of some metals on paraoxonase activity from shark Scyliorhinus canicula

Paraoxonase (PON) is an organophosphate hydrolyser enzyme which also has antioxidant properties in metabolism. Due to its crucial functions, the inhibition of the enzyme is undesirable and very dangerous. PON enzyme activity should not be altered in any case. Inhibitory investigations of this enzyme are therefore important and useful. Metal toxicology of enzymes has become popular in the recent years. Here, we report the in vitro inhibitory effects of some metal ions, including Ni²⁺, Cd²⁺, Cu²⁺ and Hg²⁺, on the activity of shark serum PON (SPON). For this purpose, we first purified the enzyme from shark Scyliorhinus canicula (LINNAEUS, 1758) serum and analysed the alterations in the enzyme activity in the presence of metal ions. The K_M and V_max is 0.227?mM and 454.545?U/mL, respectively. The results show that metal ions exhibit inhibitory effects on SPON1 at low concentrations with IC₅₀ values ranging from 0.29 to 2.00?mM. Copper was determined to be the most effective inhibitor with IC₅₀ of 0.29?mM.     

An ultrastructural and immunocytochemical study on the lymphomyeloid tissue in the embryonic kidney of the dogfish, Scyliorhinus canicula

The central role of the kidney during early development in the dogfish, Scyliorhinus canicula , is haemopoietic. The kidney is the first tissue to become lymphomyeloid and lymphocytes and developing granulocytes are found in the interstitial tissue surrounding the renal tubules. The lymphomyeloid role of the kidney is transient and does not persist after hatching. The kidney is a major immunoglobulin (Ig) containing tissue during early development as evidenced by increasing numbers of Ig–positive cells.     

Serum cholesterol and triglyceride levels in Scyliorhinus canicula (L.) during sexual maturation

A study was carried out on the serum levels of cholesterol [total (TC) and that associated with high-density lipoproteins (HDLC)] and triglyceride (TG) in 127 specimens of Scyliorhinus canicula . The values obtained were correlated with sex, size, liver weight and reproductive stage. Results showed that male dogfish have higher levels of TC and HDLC, and lower TG than female. In adult males, TC increased and HDLC decreased with both size and spermatogenesis. Females carrying capsulated eggs showed a noticeable increase in TG together with a decrease of the HDLC levels, which were apparently not related with size.     

The role of the pericardium in cardiac function in the dogfish, Squalus acanthias

Opening the pericardium to the ambient bathing fluid surrounding the in situ perfused dogfish ( Squalus acanthias ) heart caused a precipitous fall in cardiac output. Cardiac output fell by 55% despite the rise of mean input pressure from subambient, to near zero levels. Lower cardiac output caused a fall in mean output pressure but not diastolic pressure as this was set by the experimenters. With the pericardium intact, the heart was filled by suction. With an open pericardium the magnitude of negative input pressures was severely reduced. None the less, far short periods within the cardiac cycle, the heart was still able to generate subambient pressures in the atrium and so draw fluid from the central veins.     

Comparing external and internal dorsal-spine bands to interpret the age and growth of the giant lantern shark, Etmopterus baxteri (Squaliformes: Etmopteridae)

The giant lantern shark, Etmopterus baxteri, is taken as bycatch of commercial fisheries that operate in deepwater off southeastern Australia. Bands on the second dorsal spine were used to obtain age estimates. The number of bands on the external surface of the spine and within the inner dentine layer increased with animal length. Most spines had more bands on the external surface, and the rate of band formation was significantly different between the external surface and the inner dentine layer. Females had a maximum of 57 external bands and 26 internal bands, while males had up to 48 external bands and 22 internal bands. Age estimates from external bands suggest maturity (A ₅₀) at 20 years for males and 30 years for females. Internal band age estimates suggest maturity at 10.5 years for males and 11.5 years for females. Although there is a large discrepancy between these two preliminary (i.e., unvalidated) age estimates, they both suggest that E. baxteri is a long-lived and late maturing species that is likely to be susceptible to over fishing.     

Diet of spiny dogfish, Squalus acanthias Linnaeus, on the east coast, South Island, New Zealand

Stomach content data from 7283 spiny dogfish, Squalus ucunthius Linnaeus, from east coast South Island of New Zealand are presented. The major dietary components based on occurrence were 60% crustaceans and 15% fish. The principal food items were the post-larval phase of the squat lobster, Munida greguria Fabricius (30%), and the euphausiid, Nyctiphanes australis Sars (20%). Commercial fish species contributed to less than 5% of the diet. Diet of dogfish varied with dogfish size and sex. Compared to northern hemisphere studies, spiny dogfish in this study area had (1) a high proportion of crustaceans in their diet, (2) a relatively low percentage of empty stomachs, (3) a relatively high incidence of cannibalism.     

On the diel rhythms in metabolism and activity of post-hatching lesser spotted dogfish, Scyliorhinus canicula

The diel rhythms in metabolic rate ( M_R ) and activity level ( A_L ) were measured for single post-hatching dogfish (weight range, 2.76–10.61 g) at 15° C by the indirect calorimetric method of rate of oxygen consumption ( V O₂) and by video-observation respectively, over a period of 72 b. The mean VO ₂ increased from 62.0 (s.e. 2.9) mg O₂ kg⁻¹ h⁻¹ in the daylight hours to 85.5 (s.e. 3.1) mg O₂ kg⁻¹ h⁻¹ during the dark (light regíme, 12 h L: 12 h D). The simultaneous measurement of A _L also showed mean night elevation from 0.6 (s.e. 0.2) min h⁻¹ in the light phase to 14.5 (s.e. 1.6) min h⁻¹ during the darkness. Bimodal nocturnal activity (BNA) was exhibited by the post-hatching dogfish within the 12 h dark period, with V O₂ increasing from 71.4 (s.e. 2.8) mg O₂ kg⁻¹ h⁻¹ before 01.00 hours to 99.5 (s.e. 4.2) mg O₂ kg⁻¹ h⁻¹ after 01.00 hours. Similarly, A _L also increased from 8.9 (s.e. I.7)min h⁻¹ before 01.00 hours to 21.1 (s.e. 2.8) min h⁻¹ after 01.00 hours. The importance of the results presented to the natural behavioural ecology of the hatching dogfish are discussed.     

Does specific dynamic action (SDA) regulate return of appetite in the lesser spotted dogfish,Scyliorhinus caniculcla?

Specific dynamic action (SDA) and the return of appetite (RA) were measured in juvenile (weight range 10·9–16·3 g) and adult (weight range 588·8–802·2 g) Scyliorhinus canicula by means of respirometry and re-feeding trials respectively. Juvenile S. canicula consumed relatively more food than the adults at all times indicating faster rates of food processing in juvenile dogfish. At no time during the SDA effect was there any evidence that elevated levels of oxygen consumption completely prevented further food consumption in either adult or juvenile dogfish. The coefficient (Duration_SDA/Duration_RA) was similar for both adult (0·52) and juvenile (0·49) S. canicula suggesting that SDA metabolism was closely associated with the processes involved in appetite return.