AERIAL RESPIRATION IN THE LONGJAW MUDSUCKER GILLICHTHYS MIRABILIS (TELEOSTEI: GOBIIDAE)

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Abstract
When dissolved O2 measures less than 2 mg/1 ., Gillichthys mirabilis breathes aerially by means of its heavily vascularized buccopharynx. Under these conditions, the expansion of the epithelial capillaries and mucus vacuoles in the buccolpharyngeal cavity creates a lung-like surface for respiratory exchange. These histological changes apparently occur during a quiescent "period of adjustment," when all opercular movements usually cease before the fish gulps air at the water''s surface. Analysis of released gulps of air under an inverted funnel showed the fish to consume O2 and to excrete CO2 in almost direct proportion with the time that the bubble is held. Since the percentage of O2 during the period of adjustment decreases in the swimbladder, the swimbladder may provide an auxiliary O2 store for the fish''s pre-aerial respiratory conversion. A small congener resembles G. mirabilis juveniles in gulping behavior. Many other gobiids breathe aerial O2 in stagnant waters.