Browsing by Subject "Gas exchange"
Now showing items 1-2 of 2
Air breathing of aquatic burrow-dwelling eel goby, Odontamblyopus lacepedii (Gobiidae: Amblyopinae) -
Journal of Experimental Biology, 2006 - Company of BiologistsOdontamblyopus lacepedii is an eel goby that inhabits both coastal waters and intertidal zones in East Asia, including Japan. The fish excavates burrows in mudflats but, unlike the sympatric amphibious mudskippers, it does not emerge but stays in the burrows filled with hypoxic water during low tide. Endoscopic observations of the field burrows demonstrated that the fish breathed air in the burrow opening; air breathing commenced 1.3 h following burrow emersion, when water PO2 was ∼2.8 kPa, with an air-breathing frequency (fAB) of 7.3±2.9 breaths h–1 (mean ± s.d., N=5). Laboratory experiments revealed that the fish is a facultative air breather. It never breathed air in normoxic water (PO2=20.7 kPa) but started bimodal respiration when water PO2 was reduced to 1.0–3.1 kPa. The fish held air inside the mouth and probably used the gills as gas-exchange surfaces since no rich vascularization occurred in the mouth linings. As is known for other air-breathing fishes, fAB increased with decreasing water PO2. Both buccal gas volume (VB) and inspired volume (VI) were significantly correlated with body mass (Mb). At a given Mb, VI was nearly always equal to VB, implying almost complete buccal gas renewal in every breathing cycle. A temporal reduction in expired volume (VE) was probably due to a low aerial gas exchange ratio (CO2 elimination/O2 uptake). Air breathing appears to have evolved in O. lacepedii as an adaptation to aquatic hypoxia in the burrows. The acquisition of the novel respiratory capacity enables this species to stay in the burrows during low tide and extends the resident time in the mudflat, thereby increasing its chances of tapping the rich resources of the area.
Respiratory vasculatures of the intertidal air-breathing eel goby, Odontamblyopus lacepedii (Gobiidae: Amblyopinae) -
Environmental Biology of Fishes, 2008 - Springer VerlagLacking a propensity to emerge over the mud surface, the eel goby, Odontamblyopus lacepedii, survives low tide periods by continuously breathing air in burrows filled with hypoxic water. As with most marine air-breathing fishes, O. lacepedii does not possess an accessory air-breathing organ, but holds air in the buccal-opercular cavity. The present study aimed to clarify how the respiratory vasculature has been modified in this facultative air-breathing fish. Results showed that the gills apparently lacked structural modifications for air breathing, whereas the inner epithelia of the opercula were richly vascularized. Comparison with two sympatric gobies revealed that the density of blood capillaries within 10?m from the inner opercular epithelial surface in O. lacepedii (14.5 ± 3.0 capillaries mm-1; mean ± s.d., n = 3) was significantly higher than in the aquatic non-air-breathing Acanthogobius hasta (0.0 ± 0.0) but significantly lower than in the amphibious air-breathing mudskipper, Periophthalmus modestus (59.1 ± 8.5). The opercular capillary bed was supplied predominantly by the 1st efferent branchial arteries (EBA1) and drained by the opercular veins, which open into the anterior cardinal vein. Deep invaginations at the distal end of the EBA1 and the junction with EBA2 are suggestive of blood flow regulatory sites during breath-holding and apnoeic periods. It remains to be investigated how blood flow through the gills is maintained during breath holding when the buccal–opercular cavity is filled with air.