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.     

Purification of anaphase promoting complex/cyclosome from goldfish oocytes

Destruction of cyclin B is required for exit from mitosis and meiosis. A cyclin-specific ubiquitinating system, including anaphase-promoting complex/cyclosome (APC/C) is thought to be responsible for cyclin B destruction. To learn more about the molecular mechanism of cyclin B degradation, a molecular study of the ubiquitinating system in goldfish has been undertaken. For biochemical preparation of APC/C, we first conducted the cloning, sequencing and expression analysis of goldfish, Carassius auratus, cdc27 that encodes a subunit of APC/C from goldfish ovary. The deduced amino acid sequence is highly homologous to cdc27 from other species. Then recombinant goldfish Cdc27CT (C-terminal half of Cdc27) was expressed in Escherichia coli, and an antibody was raised against purified recombinant protein. Polyclonal antiserum cross-reactive with Cdc27 was obtained. By the assay using the antibody, APC/C was purified by column chromatographs.     

Effects of temperature on gonadal development of mudskipper (Periophthalmus modestus)

The effects of different temperature on gonadal development of Periophthalmus modestus were examined by histological and endocrinological analyses. Results showed that vitellogenesis and spermatogenesis were induced by high temperature treatment (30 °C). While, gonadal development did not occur in the low temperature treatment (18 °C). These results suggest that a rise in temperature plays an important role in gonadal development of this fish.     

Effect of low dissolved oxygen on the oxygen consumption rate and rhythm of the mudskipper Scartelaos gigas (Pisces, Gobiidae)

The mudskipper Scartelaos gigas is expected to experience repeated severe hypoxia in its environment. Hence, we conducted experiments on the oxygen consumption rate (OCR) and OCR rhythm of S.?gigas at low graded dissolved oxygen (DO) levels, without access to atmospheric air, to estimate its tolerance to hypoxia. A dominant circadian OCR rhythm was observed at the control DO level of 6.96?C7.78?mg?O₂/l. This rhythm was unchanged until 2.06?mg?O₂/l, even though the amplitude of the peak was somewhat diminished at 2.06?C2.87?mg?O₂/l. The OCR rhythm amplitude was greatly diminished and the rhythm period was also greatly changed at 1.23?C2.05?mg?O₂/l. Nevertheless, the mean OCR (0.11?ml?O₂/g WW/h) at 1.23?C2.05?mg O₂/l was similar to that of control (0.12?ml O₂/g?WW/h). Thus, the weakness and period change of the OCR rhythm kept the metabolic rate level similar to control. These results suggest that S.?gigas does not have normal metabolic activity at 1.23?C2.05?mg O₂/l but barely manages to endure this DO level as a pre-emergency state. This species could be inhibited under a longer maintenance period at DO level of 1.23?C2.05?mg?O₂/l or still lower. It can be concluded that S.?gigas is quite tolerant to low DO environment and may have a specific strategy for such tolerance.     

Effects of Acid Stress on Reproductive Functions in Immature Carp, Cyprinus Carpio

Changes in plasma cortisol, estoradiol-17β (E2) and 11-ketotestosterone (11-KT) levels under chronic acid exposure were examined to clarify the endocrinological effects of lowered environmental pH on gametogenesis in immature and gonadal developing carp, Cyprinus carpio. Plasma cortisol levels increased markedly 3 hours after the acid exposure and high levels were maintained for 48 hours, and then gradually decreased. Plasma E2 levels were significantly elevated and peaked at 1 week after the acid exposure. After that, E2 levels decreased gradually, but remained at significantly higher levels than the control group even at 4 weeks after the exposure. Plasma 11-KT levels showed no significant change throughout the experiment. These results indicate that acidic water disrupts the endocrine system that may have adverse effects on gametogenesis in freshwater fish.     

Expression of the Antimicrobial Peptide Piscidin 1 and Neuropeptides in Fish Gill and Skin: A Potential Participation in Neuro-Immune Interaction

Antimicrobial peptides (AMPs) are found widespread in nature and possess antimicrobial and immunomodulatory activities. Due to their multifunctional properties, these peptides are a focus of growing body of interest and have been characterized in several fish species. Due to their similarities in amino-acid composition and amphipathic design, it has been suggested that neuropeptides may be directly involved in the innate immune response against pathogen intruders. In this review, we report the molecular characterization of the fish-specific AMP piscidin1, the production of an antibody raised against this peptide and the immunohistochemical identification of this peptide and enkephalins in the neuroepithelial cells (NECs) in the gill of several teleost fish species living in different habitats. In spite of the abundant literature on Piscidin1, the biological role of this peptide in fish visceral organs remains poorly explored, as well as the role of the neuropeptides in neuroimmune interaction in fish. The NECs, by their role as sensors of hypoxia changes in the external environments, in combination with their endocrine nature and secretion of immunomodulatory substances would influence various types of immune cells that contain piscidin, such as mast cells and eosinophils, both showing interaction with the nervous system. The discovery of piscidins in the gill and skin, their diversity and their role in the regulation of immune response will lead to better selection of these immunomodulatory molecules as drug targets to retain antimicrobial barrier function and for aquaculture therapy in the future.     

Improved Seed Production of Goldstriped Amberjack Seriola lalandi under Hatchery Conditions by Injection of Triiodothyronine (T3) to Broodstock Fish

Survival of the seed of goldstriped amberjack Seriola lalandi was consistently enhanced by intramuscular injection of triiodothyronine (T₃) to the broodstock fish at a dose of 20 mg/kg body weight. Survival rates at the time of transfer to net cages (35 d after hatching) were 2.6–5.0% for the T₃ treatment while only 0.3–2.1% for the control. Survival rates 36 mo after hatching was estimated to be 12 times higher in the T₃-treated group (1.1%) than in the control (0.09%). T₃ concentration in newly spawned eggs increased from control levels of 0.3–1.0 ng/g to 68–127 ng/g 2 d after injection and subsided with successive spawns. T₃ concentration in the treated larvae was about 360 times higher than in the control upon hatching (29 np/p vs 0.08 ng/g), but became indistinguishable from the control 6 d after hatching. These results indicate injection of T₃ to the broodstock of S. lalndi to be of practical value in aquaculture of the species.