410 Donald R. Griffin 



species have an air-filled chamber directly coupled to the inner ear labyrinth. In the 

 order Ostariophysi (families Cyprinidae, Characinidae, Siluridae and Gymnotidae) 

 this involves the Weberian apparatus, an intricate structure consisting of bones, 

 cartilages and air ducts which serve to effect a mechanical coupling between the 

 swim bladder and the inner ear. Von Frisch and Stetter (1932) demonstrated 

 experimentally that the minnow suffered a considerable hearing loss when this mec- 

 hanism was damaged surgically. Air chambers can improve the sensitivity of fish's 

 hearing because sound travels almost without disturbance from one aqueous medium 

 to another, and the soft tissues of any animal are so much Hke water in their acoustical 

 properties that a " pure " fish is relatively " transparent " to underwater sound. An 

 air bubble or an air-filled chamber, on the other hand, represents a marked acoustical 

 discontinuity much as does a sohd object in the air. For a detailed consideration of 

 the acoustical properties of the catfish swim bladder see Poggendorf (1952). Other 

 fishes with keen hearing also have some type of air chamber coupled to the inner ear. 

 These structures have different morphological origins, but seem to serve the same 

 auditory function as the swim-bladder and its ramifications in the Ostariophysi. 



This anatomical correlation is an important one; for it permits one to predict 

 with some confidence that fish possessing structures that connect some air-filled 

 chamber with the inner ear labyrinth will have keen hearing. Among marine fish 

 there are very few groups which have such accessory organs of hearing. The sea 

 catfishes are anatomically similar to the freshwater catfish Ameiurus, and they might 

 be expected to have keen hearing on that account. In this connection it is interesting 

 to note that sea catfishes are listed among the species reported by Burkenroad (1931) 

 and DoBRiN (1947) as significant producers of underwater noise. The herrings 

 (family Clupeidae) are another group which one would expect to have keen hearing 

 because of their auditory structures, which have been described by Ridgewood (1891), 

 WoHLFAHRT (1936), and Evans (1940). There is an elaborate set of air passages 

 extending from the air bladder into close apposition with the membraneous labyrinth 

 of the inner ear. There are also reports that herrings are easily frightened by noises 

 made in fishing boats. Since the herring family is an abundant marine group having 

 great commercial importance, their ability to hear various frequencies of underwater 

 sound merits quantitative investigation. 



Two recent investigations have included quantitative measurements of auditory 

 thresholds in fish, and the results have amply confirmed the earher conclusions of 

 VON Frisch and others regarding the approximate equaUty of auditory thresholds 

 in fish and men, when expressed in terms of energy flux (watts/cm^). Autrum and 

 Poggendorf (1951) and Poggendorf (1952) used a caUbrated Rochelle salt crystal 

 to measure the sound pressure in a small aquarium containing single catfish {Ameuirus 

 nebulosus), and they determined auditory thresholds at frequencies from 60 to 10,000 

 c.p.s. The threshold values varied considerably, but the average of the measurements 

 at a given frequency is probably vahd within ± 10 db. Kleerekoper and Chagnon 

 (1954) have estimated auditory thresholds of a small cyprinid fish, the creek chub 

 Semotilus atromaculatus, and they report a rather narrow range of maximum sen- 

 sitivity, the thresholds being lowest at about 300 c.p.s. and rising by tenfold at 100 and 

 at 2000 c.p.s. In view of the absolute, though approximate, calibration of the measur- 

 ing instruments used by Autrum and Poggendorf, their data for the catfish provide 

 the best available evidence concerning the sensitivity of hearing in fish to underwater 



