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First published online March 2, 2006
Journal of Experimental Biology 209, 1085-1092 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02092

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Air breathing of aquatic burrow-dwelling eel goby, Odontamblyopus lacepedii (Gobiidae: Amblyopinae)

Tomas T. Gonzales^1,2,*, Masaya Katoh³ and Atsushi Ishimatsu¹

¹ Institute for East China Sea Research, Nagasaki University, Tairamachi, Nagasaki 851-2213, Japan
² Southeast Asian Fisheries Development Center, Aquaculture Department (SEAFDEC/AQD), 5021 Tigbauan, Iloilo, Philippines
³ Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Fisheries Research Agency, 148-446 Fukai-Ohta, Ishigaki, Okinawa 907-0451, Japan

View larger version (16K): [in a new window]   Fig. 1. Schematic diagram of the experimental setup used for the determination of inspired (VI) and expired (VE) volumes in Odontamblyopus lacepedii. A, amplifier; D, data-acquisition system; E, equilibration column; L, L-shaped fish chamber; R, water reservoir; S, water surface; U, ultrasonic sensor; V, ball valve; W, water bath. Sensors for a DO controller and a DO meter, thermoregulator and pump are located inside the water reservoir. Arrows indicate the direction of water flow.

View larger version (28K): [in a new window]   Fig. 2. Representative traces of air-breathing cycles in O. lacepedii. Inspired (VI) and expired (VE) volumes were obtained by subtracting a' from b' and a' from c', respectively. Note that VE can be obtained only in (A), when the inspired air was kept intact in the buccal cavity until expiration. In (B), the fish released several bubbles prior to expiration. Body mass of fish used for A and B were 60.6 g and 81.1 g, respectively.

View larger version (58K): [in a new window]   Fig. 3. Representative video sequences of an air-breathing cycle in O. lacepedii in the field burrow (top view), with corresponding footage taken from the laboratory chamber (lateral view). To breathe air, the fish approaches the surface with the mouth closed and the buccal floor and opercula adducted (white arrowhead, A). Upon breaking the surface, the mouth opens to gulp air (B) and closes immediately, with the buccal floor and opercula fully abducted (red arrowhead, C). After several minutes of breath holding, the mouth reopens to release the air (D) and the fish submerges (E). Values in the top right corner of each frame indicate the time interval (s) from the onset of inspiration. Black arrows indicate the movement of the fish. See supplementary material for further details.

View larger version (9K): [in a new window]   Fig. 4. Temporal profile of water PO2 of O. lacepedii burrows (filled circles). Each filled circle corresponds to an individual burrow. Data for burrow-water PO2 were fitted to the exponential decrease equation (y=2.48+4.87e–2.02x; r2=0.73, P<0.0001). The PO2 of free water over the mudflat during high tide is represented by the open circle with vertical line (mean ± s.d.; N=6). The arrow indicates the onset (1.3 h) of air breathing.

View larger version (12K): [in a new window]   Fig. 5. Buccal gas volume (VB) and inspired volume (VI) in relation to body mass (Mb) for O. lacepedii. Filled circles and solid regression line represent VB (VB=0.05Mb+1.62; r2=0.96, N=14). Open circles and broken regression line represent VI (VI=0.04Mb+1.47; r2=0.90, N=14). Each symbol corresponds to mean ± s.d. of 5–7 (VB) and at least 7 (VI) replicates per fish.

View larger version (11K): [in a new window]   Fig. 6. Decline in VE (expressed as % of inspired volume) as a function of breath-holding duration (BHD) in O. lacepedii during air breathing. Regression equation: VE=–0.60BHD+100.17; r2=0.88, P<0.001). VE was calculated only from fish that retained the full amount of air in the buccal cavity until expiration (see Fig. 2A). Different symbols represent individual fish (N=8).

View larger version (51K): [in a new window]   Fig. 7. Horizontal section of the head of O. lacepedii showing the absence of diverticulum and the apparent lack of respiratory vascularization in the upper (A) and lower (B) jaws. G, gill arches; P, palatine region; T, tongue. Fish body mass, 51 g. Scale bar, 1 cm.