Boleophthalmus

Abstract: This study was designed to elucidate the strategies adopted by mudskippers to handle endogenous ammonia during aerial exposure in constant darkness. Under these conditions, specimens exhibited minimal locomotory activity, and the ammonia and urea excretion rates in both Periophthalmodon schlosseri and Boleophthalmus boddaerti decreased significantly. As a consequence, ammonia accumulation occurred in the tissues of both species of mudskipper. A significant increase in urea levels was found in the liver of P. schlosseri after 24h of aerial exposure, but no similar increase was seen in the tissues of B. boddaerti. It is unlikely that these two species of mudskipper detoxified ammonia to urea during aerial exposure since B. boddaerti does not possess a complete ornithine-urea cycle (OUC) and, although all the OUC enzymes were present in P. schlosseri, the activity of carbamoyl phosphate synthetase present in the liver mitochondria was too low to render the OUC functional for ammonia detoxification. Peritoneal injection of 15NH4Cl into P. schlosseri showed that this mudskipper was capable of incorporating some of the labelled ammonia into urea in its liver. However, aerial exposure did not affect this capability and did not induce detoxification of the accumulated ammonia to urea. Mudskippers exposed to terrestrial conditions and constant darkness did, however, show significant decreases in the total free amino acid content in the liver and blood, in the case of P. schlosseri and in the muscle of B. boddaerti. No changes in the alanine or glutamine content of the muscle were found in either species. Analyses of the balance between the reduction in nitrogenous excretion and the increase in nitrogenous accumulation further revealed that these two species of mudskipper were capable of reducing their protein and amino acid catabolic rates. Such adaptations constitute the most efficient way to avoid the build-up of internal ammonia, and would render unnecessary the detoxification of ammonia through energetically expensive pathways. This finding may be the first report of a teleost fish showing a reduction in proteolysis and amino acid catabolism in response to aerial exposure.

Abstract: The aim of this study was to elucidate if the mudskipper Periophthalmodon schlosseri, in relation to its capability to survive on land, has acquired a greater capacity to detoxify ammonia than more aquatic species. The tolerance of P. schlosseri to environmental ammonia was much higher than that of another mudskipper, Boleophthalmus boddaerti, and those of other fishes. The 24, 48, and 96 h median lethal concentrations (LC50) of unionized ammonia (NH3) for P. schlosseri were 643, 556 and 536 µM, respectively. The corresponding LC50 values for B. boddaerti were 77.1, 64.0, and 60.2 µM. The relatively high tolerance of P. schlosseri to ammonia could be partially due to the presence of high activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH, aminating) in its brain. When P. schlosseri and B. boddaerti were exposed to their sublethal NH3 concentrations of 446 and 36 µM, respectively, both mudskippers detoxified ammonia by converting it to free amino acids (FAA). This led to increases in concentrations of total FAA (TFAA) in the brain, liver and muscle. Increases in TFAA concentrations in the brain were mainly due to increases in glutamine concentrations. The activities of GS and GDH in the brain of both mudskippers increased significantly after they were exposed to their respective sublethal concentrations of NH3. Urea production and excretion were not utilized as a means for environmental ammonia detoxification in these mudskippers. The most intriguing results obtained were the lack of effect on any of the parameters studied when P. schlosseri was exposed to 36 µM of environmental NH3. These results suggest that P. schlosseri might be able to maintain a low steady state level of internal ammonia during ammonia loading at a concentration which is lethal to other fishes.

Abstract: 1. The routine oxygen consumption by Periophthalmus cantonensis and Boleophthalmus chinensis in water increased geometrically, whereas that in air increased logarithmically with temperature. At temperatures of more than 20 degrees C the oxygen uptake of both species was greater in water than in air. 2. When the fishes were able freely to select either an aquatic or terrestrial habitat, the total oxygen consumption of Periophthalmus and Boleophthalmus was 236 and 110 ml/kg, h at 20 degrees C respectively; 66% (Periophthalmus) and 70% (Boleophthalmus) of the total uptake was from water, and 34 and 30% of the total uptake was from air at 20 +/- 1 degrees C. 3. Oxygen uptake of fish limited to aquatic or terrestial life was less than when they could freely select their habitat; for Periophthalmus, uptake was reduced to 83% when confined in water and to 50% in air, and for Bolephthalmus, to 65% in water and to 43% in air. 4. The proportion of oxygen uptake by the gill in water was 52% for Periophthalmus and 59% for Boleophthalmus; in air the corresponding figures were 27 and 52%. 5. The proportions of oxygen uptake via the skin in water was 48% for Periophthalmus and 36% for Boleophthalmus; in air the corresponding figures were 76 and 43%. 6. It is concluded that, on land, Periophthalmus relies mainly on its skin and Boleophthalmus relies mainly on its gills.

Abstract: The three mudskippers—Periophthalmus chrysospilos, Boleophthalmus boddaerti, and Periophthalmodon schlosseri—occupy the same macrohabitat in Singapore but have different behaviors. Correlations were made between differences in behavior and morphological adaptations of their gills to tolerate terrestrial exposure.P. schlosseri has branched gill filaments, thick gill rods, and fused secondary lamellae which enable them to better adapt to a terrestrial than an aquatic environment. Of the three mudskippers, P. chrysospilos gills are the shortest. They are also bent and poorly developed for aquatic respiration. B. boddaerti gills consist of numerous long filaments and have the largest gill area of the three mudskippers. These features suggest that B. boddaerti gills function more efficiently as a respiratory organ in water than in air.Gill surfaces of all three mudskippers are highly convoluted to increase surface area.

Abstract: Analyse et comparaison de la morphometrie des ouies et des surfaces de peau impliquees dans la respiration de P. chrysospilos, B. boddaerti et P. schlosseri en fonction de leur volume corporel et de leur capacite a respirer sur la terre. Implication des resultats dans l'adaptation de strategies comportementales de ces animaux en fonction de leur habitat naturel