Anterior adhesive areas and adjacent secretions in the parasitic flatworms Decacotyle lymmae and D. tetrakordyle (Monogenea: Monocotylidae) from the gills of stingrays

The monogeneans Decacotyle lymmae and D. tetrakordyle (Monocotylidae: Decacotylinae), from gills of the dasyatid stingrays Taeniura lymma and Pastinachus sephen, respectively, have a single aperture for adhesive secretion on each side of the anterior ventrolateral region. Rod-shaped bodies (S1) and electron-dense spherical secretion (S2) exit through specialised ducts opening adjacent to one another within these apertures. The S1 bodies are 230 +/- 11 nm wide and greater than or equal to4 mum long in D. lymmae and 240 +/- 9 nm wide and greater than or equal to3.3 mum long in D. tetrakordyle. The S2 bodies have a diameter of 88 +/- 7 nm in D. lymmae and 65 +/- 6 nm in D. tetrakordyle. The apertures are unusual in being extremely small (internal diameter, 3-5 mum). Each aperture has a slit-like surface opening as small as 160 nm wide, surrounded by muscle fibres indicating that they may be opened and closed. The aperture is also surrounded and underlain by muscle fibres that may aid in secretion from, or even eversion of, the tissue within the aperture. Sensilla/cilia are also found within the apertures. Additional secretions from anteromedian and anterolateral glands (body glands), each containing granular secretions, occur in profusion and exit anteriorly and posteriorly to the position of the apertures, through duct openings in the general body tegument. These granular secretions do not appear to be associated with anterior adhesion. Both species show similarities in aperture, underlying tissue, sense organ, and secretion detail, in accordance with findings from other monogenean genera, and which supports the importance of such data for phylogenetic studies.

Moravecia australiensis n. g., n. sp (Dracunculoidea : Guyanemidae) from the gills of the green porcupine fish Tragulichthys jaculiferus (Cuvier) in Australia

A new dracunculoid genus and species, Moravecia australiensis, is described from gill-filaments of the green porcupine fish Tragulichthys jaculiferus (Cuvier) (Tetraodontiformes: Diodontidae) from Moreton Bay, Queensland, Australia. Abundant mobile larvae and a few adult males with females occurred in the gill-filament between the epithelial basement membrane and efferent artery. Gills of all 69 fish examined contained larvae. Eleven harboured adult nematodes of a previously undescribed species belonging to the family Guyanemidae. The new species is placed within a newly proposed genus because it differs from the four existing genera in the family in possessing fine cuticular transverse striations, two forward protruding cephalic elevations, a circumoral elevation, a small triangular mouth surrounded by six cephalic papillae arranged in two lateral clusters of three each and a pair of large lateral amphids. Males have two pairs of pedunculate caudal papillae supporting the caudal alae. A key to the genera of the Guyanemidae is presented.

Partitioning of respiration between the gills and air-breathing organ in response to aquatic hypoxia and exercise in the Pacific tarpon, Megalops cyprinoides

The evolution of air-breathing organs (ABOs) is associated not only with hypoxic environments but also with activity. This investigation examines the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon. The two-species cosmopolitan genus Megalops is unique among teleosts in using swim bladder ABOs in the pelagic marine environment. Small fish ( 58 - 620 g) were swum at two sustainable speeds in a circulating flume respirometer in which dissolved oxygen was controlled. For fish swimming at 0.11 m s(-1) in normoxia (Po-2 = 21 kPa), there was practically no air breathing, and gill oxygen uptake was 1.53 mL kg(-0.67) min(-1). Air breathing occurred at 0.5 breaths min(-1) in hypoxia ( 8 kPa) at this speed, when the gills and ABOs accounted for 0.71 and 0.57 mL kg(-0.67) min(-1), respectively. At 0.22 m s(-1) in normoxia, breathing occurred at 0.1 breaths min(-1), and gill and ABO oxygen uptake were 2.08 and 0.08 mL kg(-0.67) min(-1), respectively. In hypoxia and 0.22 m s(-1), breathing increased to 0.6 breaths min(-1), and gill and ABO oxygen uptake were 1.39 and 1.28 mL kg(-0.67) min(-1), respectively. Aquatic hypoxia was therefore the primary stimulus for air breathing under the limited conditions of this study, but exercise augmented oxygen uptake by the ABOs, particularly in hypoxic water.

Urea based osmoregulation and endocrine control in elasmobranch fish with special reference to euryhalinity

Since the landmark contributions of Homer Smith and co-workers in the 1930s there has been a considerable advance in our knowledge regarding the osmoregulatory strategy of elasmobranch fish. Smith recognised that urea was retained in the body fluids as part of the 'osmoregulatory ballast' of elasmobranch fish so that body fluid osmolality is raised to a level that is iso- or slightly hyper-osmotic to that of the surrounding medium. From studies at that time he also postulated that many marine dwelling elasmobranchs were not capable of adaptation to dilute environments. However, more recent investigations have demonstrated that, at least in some species, this may not be the case. Gradual acclimation of marine dwelling elasmobranchs to varying environmental salinities under laboratory conditions has demonstrated that these fish do have the capacity to acclimate to changes in salinity through independent regulation of Na+, Cl- and urea levels. This suggests that many of the presumed stenohaline marine elasmobranchs could in fact be described as partially euryhaline. The contributions of Thomas Thorson in the 1970s demonstrated the osmoregulatory strategy of a fully euryhaline elasmobranch, the bull shark, Carcharhinus leucas, and more recent investigations have examined the mechanisms behind this strategy in the euryhaline elasmobranch, Dasyatis sabina. Both partially euryhaline and fully euryhaline species utilise the same physiological processes to control urea, Na+ and Cl- levels within the body fluids. The role of the gills, kidney, liver, rectal gland and drinking process is discussed in relation to the endocrine control of urea, Na+ and Cl- levels as elasmobranchs acclimate to different environmental salinities. (C) 2003 Elsevier Inc. All rights reserved.

Freshwater to seawater acclimation of juvenile bull sharks ( Carcharhinus leucas): plasma osmolytes and Na +/K +-ATPase activity in gill, rectal gland, kidney and intestine

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater ( SW). Juvenile C. leucas captured in FW ( 3 mOsm l(-1) kg(-1)) were acclimated to SW ( 980 - 1,000 mOsm l(-1) kg(-1)) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l(-1) kg(-1). In SW, bull sharks had significantly higher plasma osmolarities ( 940 mOsm l(-1) kg(-1)) than FW-acclimated animals and were slightly hypoosmotic to the environment. Plasma Na+, Cl-, K+, Mg2+, Ca2+, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na+/ K+-ATPase activity. Na+/ K+-ATPase activity in the gills and intestine was less than 1 mmol Pi mg(-1) protein h(-1) and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na+/ K+-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na+/ K+-ATPase activity was 5.6 +/- 0.8 and 9.2 +/- 0.6 mmol Pi mg(-1) protein h(-1), respectively. Na+/ K+-ATPase activity in the kidney of FW and SW acclimated animals was 8.4 +/- 1.1 and 3.3 +/- 1.1 Pi mg(-1) protein h(-1), respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.

Effects of temperature, salinity, desiccation and chemical treatments on egg embryonation and hatching success of Benedenia seriolae (Monogenea : Capsalidae), a parasite of farmed Seriola spp.

The effects of temperature and salinity on the embryonation period and hatching success of eggs of Benedenia seriolae were investigated. Temperature strongly influenced embryonation period; eggs first hatched 5 days after laying at 28 degreesC and 16 days after laying at 14 degreesC. The relationship between temperature and embryonation period is described by quadratic regression equations for time to first and last hatching. Hatching success was >70% for B. seriolae eggs incubated at temperatures from 14 to 28 degreesC. However, no B. seriolae eggs embryonated and hatched at 30 degreesC and