Control of the respiratory mode in air-breathing fishes

SUMMARY The present study examined the role of branchial and orobranchial O2 chemoreceptors in the cardiorespiratory responses, aquatic surface respiration (ASR), and the development of inferior lip swelling in tambaqui during prolonged (6 h) exposure to hypoxia. Intact fish (control) and three groups of denervated fish (bilateral denervation of cranial nerves IX+X(to the gills), of cranial nerves V+VII (to the orobranchial cavity) or of cranial nerves V alone), were exposed to severe hypoxia(PwO2=10 mmHg) for 360 min. Respiratory frequency(fr) and heart rate (fh) were recorded simultaneously with ASR. Intact (control) fish increased fr, ventilation amplitude (VAMP) and developed hypoxic bradycardia in the first 60 min of hypoxia. The bradycardia,however, abated progressively and had returned to normoxic levels by the last hour of exposure to hypoxia. The changes in respiratory frequency and the hypoxic bradycardia were eliminated by denervation of cranial nerves IX and X but were not affected by denervation of cranial nerves V or V+VII. The VAMP was not abolished by the various denervation protocols. The fh in fish with denervation of cranial nerves V or V+VII, however, did not recover to control values as in intact fish. After 360 min of exposure to hypoxia only the intact and IX+X denervated fish performed ASR. Denervation of cranial nerve V abolished the ASR behavior. However, all (control and denervated (IX+X, V and V+VII) fish developed inferior lip swelling. These results indicate that ASR is triggered by O2 chemoreceptors innervated by cranial nerve V but that other mechanisms, such as a direct effect of hypoxia on the lip tissue, trigger lip swelling.

Section: Gill Ventilatory Responses To Hypoxiamentioning

confidence: 99%

The role of branchial and orobranchial O2 chemoreceptors in the control of aquatic surface respiration in the neotropical fish tambaqui(Colossoma macropomum): progressive responses to prolonged hypoxia

Florindo

Leite

Kalinin

et al. 2006

“…They suggested that an ABO-O 2 chemoreceptor would be advantageous in the regulation of cardiac responses to an air-breathing event. A common pattern of cardiac arrhythmia found in fishes during an air-breathing event is inspiration-induced tachycardia followed by the gradual onset of bradycardia as the ABO-O 2 content falls, leading to pronounced bradycardia with exhalation (Farrell, 1978;Johansen et al, 1968a;Singh and Hughes, 1973;Smatresk, 1988;Smatresk, 1990). Therefore, an ABO-O 2 chemoreceptor may be important in the modulation of mechanoreceptor and other stimuli affecting air-breathing tachycardia, in attenuating tachycardia as ABO-O 2 declines and in terminating the breath when ABO-P O 2 becomes too low to promote O 2 uptake (Graham and Baird, 1984).…”

Section: Abo-o 2 Chemoreceptorsmentioning

confidence: 99%

Effect of aerial O2 partial pressure on bimodal gas exchange and air-breathing behaviour inTrichogaster leeri

Alton

White

Seymour

2007

P O 2 in the ABO at the end of apnoea. This increased with increasing P O 2 ,air , suggesting that ABO-P O 2 is not regulated at a constant level by internal chemoreceptors. Furthermore, mean V O 2 ,ap increased with increasing P O 2 ,air , indicating that the observed increase in V O 2/breath with increasing P O 2 ,air was facilitated not only by an increase in apnoea duration but also by an increase in the air-blood P O 2 gradient.

“…histophorus took a single, rapid breath (held for 1-2·s) from each gas phase before removing or adding to it. This suggests that it was able to sense the gas-phase P O ∑ immediately upon inspiration, a reasonable assumption based on the occurrence of O 2 chemoreceptors on the branchial arches and in the buccal cavities of most fishes (Jones and Milsom, 1982;Smatresk, 1988;Graham, 1997;Milsom et al, 2002). The mudskipper aerial respiratory surfaces line the buccal, branchial, pharyngeal and opercular cavities (Schöttle, 1932;Hora, 1935a,b;Stebbins and Kalk, 1961;Gibson, 1969;Graham, 1997;Clayton, 1993), so it is reasonable to expect that air held in the mouth would contact the O 2 sensors.…”

Section: Air-deposition Behavior Function and Rate Studiesmentioning

confidence: 94%

Burrow air phase maintenance and respiration by the mudskipperScartelaos histophorus(Gobiidae: Oxudercinae)

Lee

Martinez

Hertzberg

et al. 2005

SUMMARY A laboratory burrow and mudflat system was used to examine aspects of burrow air-phase maintenance and utilization by the amphibious mudskipper Scartelaos histophorus. While confined to its burrow during simulated`high tide', this species respires both aquatically and aerially, in the latter case utilizing an air phase it had established by transporting air into the burrow during simulated `low tide'. Over the course of `high-tide'confinement, burrow-water PO2 declines, making the air phase more important for respiration; the burrow-water O2tension eliciting air-phase respiration is 4.8±0.2 kPa. At `low tide',when the fish has access to air, it deposits new air in the air phase by transporting gulps into the burrow and releasing them. Observed air-deposition rates for both males and females were 12.3±4.5 trips h-1. All of the fish tested (N=8 individuals + 2 pairs) deposited air and responded to experimental air-phase withdrawal by replacing the air (72 of 74 tests, 97.3%). Also, repeated tests with one fish showed that experimental reduction of the air-phase PO2 by mixing with N2 elicited a gas-expelling behavior at O2 levels less than 10.3 kPa. At O2 levels greater than 10.3 kPa, the fish left the air phase intact and added to it by depositing surface air.