A systemic secondary vessel system is present in the teleost fish Tandanus tandanus and absent in the elasmobranchs Carcharhinus melanopterus and Rhinobatos typus and in the dipnoan Neoceratodus forsteri

Hydraulic control of tuna fins: A role for the lymphatic system in vertebrate locomotion

The lymphatic system in teleost fish has genetic and developmental origins similar to those of the mammalian lymphatic system, which is involved in immune response and fluid homeostasis. Here, we show that the lymphatic system of tunas functions in swimming hydrodynamics. Specifically, a musculo-vascular complex, consisting of fin muscles, bones, and lymphatic vessels, is involved in the hydraulic control of median fins. This specialization of the lymphatic system is associated with fish in the family Scombridae and may have evolved in response to the demand for swimming and maneuvering control in these high-performance species.

Ammonia transport across the skin of adult rainbow trout (Oncorhynchus mykiss) exposed to high environmental ammonia (HEA)

Recent molecular evidence points towards a capacity for ammonia transport across the skin of adult rainbow trout. A series of in vivo and in vitro experiments were conducted to understand the role of cutaneous ammonia excretion (J amm) under control conditions and after 12-h pre-exposure to high environmental ammonia (HEA; 2 mmol/l NH4HCO3). Divided chamber experiments with bladder-catheterized, rectally ligated fish under light anesthesia were performed to separate cutaneous J amm from branchial, renal, and intestinal J amm. Under control conditions, cutaneous J amm accounted for 4.5 % of total J amm in vivo. In fish pre-exposed to HEA, plasma total ammonia concentration increased 20-fold to approximately 1,000 μmol/l, branchial J amm increased 1.5- to 2.7-fold, and urinary J amm increased about 7-fold. Urinary J amm still accounted for less than 2 % of total J amm. Cutaneous J amm increased 4-fold yet amounted to only 5.7 % of total J amm in these fish. Genes (Rhcg1, Rhcg2, Rhbg, NHE-2, v-type H(+)-ATPase) known to be involved in ammonia excretion at the gills of trout were all expressed at the mRNA level in the skin, but their expression did not increase with HEA pre-exposure. In vitro analyses using [(14)C] methylamine (MA), an ammonia analog which is transported by Rh proteins, demonstrated that MA permeability in isolated skin sections was higher in HEA pre-exposed fish than in control fish. The addition of basolateral ammonia (1,000 μmol/l) to this system abolished this increase in permeability, suggesting ammonia competition with MA for Rh-mediated transport across the skin of HEA pre-exposed trout; this did not occur in skin sections from control trout. Moreover, in vitro J amm by the skin of fish which had been pre-exposed to HEA was also higher than in control fish in the absence of basolateral ammonia, pointing towards a possible cutaneous ammonia loading in response to HEA. In vitro MA permeability was reduced upon the addition of amiloride (10(-4) mol/l), but not phenamil (10(-5) mol/l) suggesting a role for a Na/H-exchanger (NHE) in cutaneous ammonia transport, as has been previously described in the skin of larval fish. Overall, it appears that under control conditions and in response to HEA pre-exposure, the skin makes only a very minor contribution to total J amm, but the observed increases in cutaneous J amm in vivo and in cutaneous J amm and MA permeability in vitro demonstrate the capacity for ammonia transport in the skin of adult trout. It remains unclear if this capacity may become significant under certain environmental challenges or if it is merely a remnant of cutaneous transport capacity from early life stages in these fish.

Differences in activity level between cownose rays (Rhinoptera bonasus) and Atlantic stingrays (Dasyatis sabina) are related to differences in heart mass, hemoglobin concentration, and gill surface area

Aquatic animals are faced with the challenge of extracting oxygen from water, a medium that is metabolically expensive to ventilate and that contains just a fraction of the oxygen concentration relative to air, yet the physiologies of fishes have evolved to support a wide range of activity levels in nature. Oxygen delivery components, including gill surface area (oxygen uptake), blood chemistry (oxygen transport), and the heart (system pump), have been positively correlated to activity level in teleost fishes, yet relatively little is known about how these components are related to activity in elasmobranches. The current study addresses this question by examining heart mass, hemoglobin concentration, hematocrit level, and gill surface area in wild-caught representatives of the benthic Atlantic stingray (Dasyatis sabina) and active cownose ray (Rhinoptera bonasus). Allometric scaling exponents are similar for all four measures between the study species. Heart mass, gill surfaces areas, and hemoglobin concentrations were 2.1 times, approximately 7.1 times, and 2.0 times higher, respectively, in active cownose rays, when compared to benthic Atlantic stingrays, after correcting for differences in body mass. When considered in the context of functional plasticity within the oxygen delivery systems of benthic and active species, data from the current study indicate that higher activity levels in cownose rays are supported by modifications that, at least in part, are likely to enhance oxygen uptake.

Evaluation of critical care blood analytes assessed with a point-of-care portable blood analyzer in wild and aquarium-housed elasmobranchs and the influence of phlebotomy site on results

OBJECTIVE

To establish reference ranges for critical care blood values measured in wild and aquarium-housed elasmobranchs by use of a point-of-care (POC) blood analyzer and to compare values on the basis of species category (pelagic, benthic, or intermediate) and phlebotomy site.

DESIGN

Cross-sectional study.

ANIMALS

66 wild and 89 aquarium-housed elasmobranchs (sharks and rays).

PROCEDURES

Aquarium-housed elasmobranchs were anesthetized for sample collection; wild elasmobranchs were caught via hook and line fishing, manually restrained for sample collection, and released. Blood was collected from 2 sites/fish (dorsal sinus region and tail vasculature) and analyzed with the POC analyzer. Reference values of critical care blood analytes were calculated for species most represented in each population. Values were compared on the basis of species categorization (pelagic, intermediate, or benthic) and collection site.

RESULTS

Oxygen saturation and circulating concentrations of lactate and glucose were significantly different among aquarium-housed pelagic, intermediate, and benthic species. Lactate concentration was significantly different among these categories in wild elasmobranchs. Significant differences were detected between samples from the 2 collection sites for all blood analytes. In both study populations, pH and lactate values were infrequently < 7.2 or > 5 mmol/L, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Brevity of handling or chemical restraint may have reduced secondary stress responses in fish because extreme variations in blood analyte values were infrequent. Sample collection site, species categorization, acclimation to handling, and restraint technique should be considered when assessing values obtained with the POC analyzer used in this study for blood analytes and immediate metabolic status in elasmobranchs.

Structural basis for control of secondary vessels in the long-finned eel Anguilla reinhardtii

Histological sections of primary segmental arteries and associated interarterial anastomoses and secondary vessels from the long-finned eel Anguilla reinhardtii were examined by light and transmission electron microscopy. Interarterial anastomoses were found to originate from the primary vasculature as depressions through the tunica intima and media, from where they ran perpendicularly to the adventitial layer, before coiling extensively. From here the anastomoses travelled a relatively linear path in the outer margin of the adventitia to anastomose with a secondary vessel running in parallel with the primary counterpart. In contrast to findings from other species, secondary vessels had a structure quite similar to that of primary vessels; they were lined by endothelial cells on a continuous basement membrane, with a single layer of smooth muscle cells surrounding the vessel. Smooth muscle cells were also found in the vicinity of interarterial anastomoses in the adventitia, but these appeared more longitudinally orientated. The presence of smooth muscle cells on all aspects of the secondary circulation suggests that this vascular system is regulated in a similar manner as the primary vascular system. Because interarterial anastomoses are structurally integrated with the primary vessel from which they originate, it is anticipated that flow through secondary vessels to some extent is affected by the vascular tone of the primary vessel. Immunohistochemical studies showed that primary segmental arteries displayed moderate immunoreactivity to antibodies against 5-hydroxytryptamine and substance P, while interarterial anastomoses and secondary vessels showed dense immunoreactivity. No immunoreactivity was observed on primary or secondary arteries against neuropeptide Y or calcitonin gene-related peptide.

The blood volumes of the primary and secondary circulatory system in the Atlantic cod Gadus morhua L, using plasma bound Evans Blue and compartmental analysis

The volume of the primary (PCS) and secondary (SCS) circulatory system in the Atlantic cod Gadus morhua was determined using a modified dye dilution technique. Cod (N=10) were chronically cannulated in the second afferent branchial artery with PE-50 tubing. Evans Blue dye was bound to harvested fish plasma at a concentration of 1 mg dye ml(-1) plasma, and injected at a concentration of 1 mg kg(-1) body mass. Serial sampling from the cannula produced a dye dilution curve, which could be described by a double exponential decay equation. Curve analysis enabled the calculation of the primary circulatory and total distribution volume. The difference between these volumes is assumed to be the volume of the SCS. From the dilution curve, it was also possible to calculate flow rates between and within the systems. The results of these experiments suggest a plasma volume in the PCS of 3.42+/-0.89 ml 100 g(-1) body mass, and in the SCS of 1.68+/-0.35 ml 100 g(-1) body mass (mean +/- S.D.) or approximately 50% that of the PCS. Flow rates to the SCS were calculated as 2.7% of the resting cardiac output. There was an allometric relationship between body mass and blood volumes. Increasing condition factor showed a tendency towards smaller blood volumes of the PCS, expressed as percentage body mass, but this was not evident for the volume of the SCS.