FIELD AND LABORATORY OBSERVATIONS ON 



DIURNAL SWIM BLADDER INFLATION-DEFLATION IN LARVAE OF 



GULF MENHADEN, BREVOORTIA PATRONUS 



D. E. Hoss 1 AND G. Phonlor 2 



ABSTRACT 



Diurnal swim bladder inflation-deflation in gulf menhaden larvae was studied at sea and in the 

 laboratory. At sea, the larvae filled their swim bladders at night and deflated them during the day. 

 Laboratory experiments in which the larvae were either prevented or allowed to reach the air-water 

 interface demonstrated that the larvae fill their swim bladder each night by swallowing air. These 

 results agree with the findings of other investigators and suggest that diurnal swim bladder inflation 

 may be a common characteristic in the late stage larvae of clupeoid species. 



The swim bladder in fishes has been assigned var- 

 ious functions, the most widespread being the reg- 

 ulation of buoyancy. Recent work on clupeoid 

 species, however, has shown that the function of 

 the swim bladder changes with ontogeny In adults 

 of at least two clupeoids — Atlantic herring, 

 Clupea harengus, and Atlantic menhaden, Bre- 

 voortia tyrannus — the swim bladder is thought to 

 serve as a reserve of gas for the adjustment of 

 hydrostatic pressure in the gas-filled bulla, allow- 

 ing the bulla membrane to maintain acoustic 

 sensitivity independently of depth. The swim 

 bladder's role as a buoyancy regulating organ is 

 secondary (Blaxter and Hunter 1982). During the 

 late larval stages of some clupeoids, however, 

 buoyancy provided by an inflated swim bladder 

 may have an important function. Hunter and San- 

 chez (1976), working with the pelagic larvae of the 

 northern anchovy, Engraulis mordax, proposed 

 that an observed diurnal inflation and deflation of 

 the swim bladder by larvae is an energy-sparing 

 mechanism. In this case, one function of the in- 

 flated swim bladder is to provide buoyancy that 

 allows the larvae to "rest" during the night when 

 they are unable to see to feed. This diurnal infla- 

 tion and deflation of the swim bladder has also 

 been reported for other larval clupeoids by Uotani 

 (1973). 



The objective of this study was to determine if a 

 diurnal swim bladder inflation-deflation rhythm 

 exists in larval gulf menhaden, Brevoortia patro- 



1 Southeast Fisheries Center Beaufort Laboratory, National 

 Marine Fisheries Service, NOAA, Beaufort, NC 28516-9722. 



2 Fundacao Universidade do Rio Grande, 96.200 Rio Grande, 

 RS, Brazil. 



nus, under natural conditions and, if so, to evalu- 

 ate the mechanism of inflation in the laboratory. 

 The swim bladder in gulf menhaden is similar to 

 that described for Atlantic menhaden by Hoss and 

 Blaxter (1981). In the Atlantic species the anlage 

 of the swim bladder is present at 10 mm standard 

 length (SL), and the pro-otic bullae first appear at 

 12.5 mm and may contain gas soon after. The swim 

 bladder first contains bubbles of gas in 13 mm SL 

 larvae, and the lateral line first appears in larvae 

 of about 17 mm. In the fully developed system, 

 narrow ducts connect the swim bladder to the 

 gas-filled bullae which are close to the labyrinth of 

 the inner ear. The bullae-swim bladder system is 

 in turn connected to the extensive lateral line on 

 the head of adult fish through a membrane in the 

 skull. As in other clupeoid species (Blaxter and 

 Hunter 1982), menhaden apparently swallow air 

 to initially fill both the bullae and the swim blad- 

 der. As there is no evidence for gas secretion in 

 menhaden, it is also assumed that they replace 

 lost gas by regularly swallowing air into the 

 alimentary canal and then by transferring it to 

 the swim bladder through the pneumatic duct. 

 The swim bladder is deflated by diffusion and by 

 reversing gas movement in the above pathway. 

 Unlike some clupeoids, menhaden have no direct 

 connection between the swim bladder and the anal 

 opening (Tracy 1920). 



METHODS 



At Sea 



Gulf menhaden larvae were obtained in the 

 northern Gulf of Mexico off Southwest Pass, La., 



Manuscript accepted January 1984. 

 FISHERY BULLETIN: VOL. 82, NO. 3, 1984. 



513 



