Alfredo Damasceno-Oliveira

Shell nacre ultrastructure and depressurisation dissolution in the deep-sea hydrothermal vent mussel Bathymodiolus azoricus

This study describes the micro-morphological features of the shell nacre in the vent mytilid Bathymodiolus azoricus collected along a bathymetric gradient of deep-sea hydrothermal vents of the mid-Atlantic ridge (MAR). Pressure-dependent crystallisation patterns were detected in animals subjected to post-capture hydrostatic simulations. We provide evidence for the following: (1) shell micro morphology in B. azoricus is similar to that of several vent and cold-seep species, but the prismatic shell layers may vary among bathymodiolids; (2) nacre micro-morphology of mussels from three vent sites of the MAR did not differ significantly; minor differences do not appear to be related to hydrostatic pressure, but rather to calcium ion availability; (3) decompression stress may cause drop off in pH of the pallial fluid that damages nascent crystals, and in a more advanced phase, the aragonite tablets as well as the continuous layer of mature nacre; and (4) adverse effects of decompression on calcium salt deposition in shells was diminished by re-pressurisation of specimens. The implications of the putative influence of hydrostatic pressure on biomineralisation processes in molluscs are discussed.

THE INFLUENCE OF HYDROSTATIC PRESSURE ON SHELL MINERALIZATION OF ANODONTA CYGNEA: A COMPARATIVE STUDY WITH A HYDROTHERMAL VENT BIVALVE BATHYMODIOLUS AZORICUS

ABSTRACT The objective of this study was to determine at what level the shell mineralization of Anodonta cygnea, a shallow freshwater bivalve, is influenced by external physical—chemical factors, mainly concerning the habit and microstructure of the calcium carbonate crystals. A detailed examination of the inner shell layers of A. cygnea was carried out by scanning electron microscopy in animals living under natural environment conditions and after being exposed to artificially high hydrostatic pressure. Groups of 6 animals were exposed to different hydrostatic pressure (10, 20, 40, or 80 bar) in a hyperbaric chamber for 10 days. In general, we noted that the high pressure induced strong changes in the microstructure of all regions of the shell inner layer in A. cygnea, probably by altering organic matrix deposition, under every hyperbaric value. In fact, observations of the prismatic layer showed some significant alterations, presenting fibrous spherulitic crystalline arrangements instead of the nondenticular composite crystals. At the beginning of the nacreous layer, experimental animals showed several (5–7) superimposed lamellae consisting of unconnected round tablets. In the following regions, the nacreous layer with hexagonal-rhombohedral crystals displayed an intense growth resembling columnar formations resulting from a greater number of mineral layers, many more than would be expected. A similar phenomenon was also revealed in the inner palliai line regions of the exposed A. cygnea bivalves, with simultaneous visualization of more than 10–15 layers of nacre in contrast with 3–4 seen in natural situations. Curiously, similarly altered microstructures were observed in shell calcareous layers of a hydrothermal vent deepsea bivalve Bathymodiolus azoricus, particularly in the nacreous layer. This natural occurrence, together with the experimental work on A. cygnea, might imply that hydrostatic pressure is a physical parameter of great importance in microstructure definition. The basic mechanism is probably related to deficient chitin (or similar) polymerization, which promotes the vertical growth of the nacre crystals.

Effect of Reduction in Water Salinity on Osmoregulation and Survival of Large Atlantic Salmon Held at High Water Temperature

Abstract We examined the possible ameliorating effects of reduced salinity (28‰) on the physiological performance of large Atlantic salmon Salmo salar initially reared at 35‰ and exhibiting osmo-ionoregulatory disturbances in high seasonal water temperatures (>18°C). Considerable differences were observed in the behavior, survival, and plasma values for cortisol, osmolality, and chloride after 3 d, with fish from the 28‰ salinity regime approaching basal levels (cortisol: 8.0 ± 1.7 mmol/L; osmolality: 374.3 ± 6.8 milliosmols per kilogram [mosmols/kg]; [Cl-]: 170.5 ± 3.8 mmol/L [mean ± SE]) and fish from full-strength seawater showing a further decrease in osmoregulatory capacity (cortisol: 33.7 ± 5.0 mmol/L; osmolality: 411.4 ± 9.7 mosmols/kg; [Cl-]: 189.1 ± 6.8 mmol/L). Two weeks later, fish kept at 28‰ still had a normal osmoregulatory capacity and exhibited a significant increase in condition factor, whereas many fish (70%) in full-strength seawater had died. These results indicate a limited capacity f...

Growth and osmoregulation in Salmo salar L. juveniles 1+, 1½ + and 2+ reared under restrained salinity

The freshwater phase of Atlantic salmon Salmo salar L vary between one and eight years. The reduction of the freshwater phase is desirable to reduce freshwater usage, human resources and to increase year round availability of pan-sized salmon. Three trials were conducted to investigate the possibility of supply the market in a year-round basis, with pan-sized Atlantic salmon Salmo salar L. (250-300 g) in Portugal (southern limit of the natural distribution of this species). This study primarily aimed to compare the osmoregulatory ability and growth of different fish sizes, smolts 1+ (trial 1), 1.5+ (trial 2) and 2+ (trial 3), in freshwater and seawater conditions. Additionally, effects of photoperiod were determined in smolts 1.5+ (trial 2) for both freshwater and seawater groups. The increments in the plasma osmolality and chlorine concentrations after seawater transfer suggest an identical development in the hypo-osmoregulation capacity among the different age classes. In all trials, weight gain was smaller after 30 d of saltwater transfer when compared to fish reared in freshwater. However, the growth depression was temporary. Seawater group showed a compensatory growth in the immediate months, which permitted an improvement in growth rates. At the end of trials there were minor differences on growth performance between freshwater and seawater groups. Specific growth rates varied between 0.7 and 1.0 % day-1, according to the age and /or size and transfer season.

Pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels in maturing female flounder Platichthys flesus under hydrostatic pressure simulating vertical migrations

Abstract Rhythmic vertical migration is a widespread feature among teleost species and the ultimate reasons for this behaviour could be as diverse as transport, feeding, predator avoidance or reproduction strategies. A rhythmic vertical migration implies that a fish will experience associated cyclic pressure changes. We examined the effect of 14-day exposure to cyclic variations in hydrostatic pressure (HP) and to elevated constant HP on pituitary levels of two types of gonadotropin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), in maturing but not ovulating female European flounder (Platichthys flesus). Fish were exposed to cyclic HP with a tidal period of 12.4 h and an amplitude of 600 kPa, between 200 and 800 kPa (environmentally realistic vertical migration), to constant absolute HP of 800 kPa, and to a maximum 1 m height water column. Flounder pituitary FSH content was remarkably higher under cyclic HP conditions than under constant normal or elevated HP conditions. In fact, pituitary FSH levels were undetectable, irrespective of the constant HP regimen. By contrast, pituitary LH levels showed no significant differences between the different groups at the end of the experimental period. This study describes an important alteration of the brain–pituitary–gonad (BPG) axis provoked by exposure to HP fluctuations, which mimic conditions in nature. The results indicate that levels of FSH in female European flounder are influenced by rhythmic vertical migrations.