FISHERY BULLETIN: VOL. 84, NO. 3 



exhibited swim-bladder rupture (1 specimen had 2 

 points of rupture), and 27 (79%) had tissue emphy- 

 sema. 



Significantly more angling-caught black sea bass 

 had oral protrusions than those caught by trawling 

 (X 2 = 138, df = 1, P « 0.001). For trawl-caught 

 red snappers, significantly more fish caught aboard 

 the Georgia Bulldog (26 of 39) had oral eversions 

 than those caught aboard the Blue Fin (0 of 8) (x 2 

 = 5.34, df = 1, P < 0.025). No other comparisons 

 for combinations of symptoms, species, and gear 

 types yielded significant results. However, all oral 

 eversions noted for Mycteroperca groupers were 

 produced by Georgia Bulldog trawling gear, and 

 those noted for sand perch were produced by 

 angling gear. 



DISCUSSION 



Differences Due to Species and Gear 



Differences between fish species (captured by 

 identical gear) in the type and frequency of gut 

 displacement are likely due to differences in bone 

 structure and relative swim-bladder volume. Except 

 for planehead filefish, which exhibited all forms of 

 external evidence, those species which experienced 

 frequent oral eversions did not present cloacal ever- 

 sions and vice versa (Table 1; refer also to the anal- 

 yses of categorized data). In this study the leather- 

 jackets (Balistidae) and angelfishes (Holacanthidae) 

 experienced high frequencies of gut displacements 

 toward the cloacal area. These taxa have a relatively 

 restricted pharyngeal area and the leatherjackets 

 have a bony sternum which further defines a "path 

 of least resistance" toward the cloaca. Other fishes 

 which may be similarly susceptible to cloacal pro- 

 trusions include other balistids, acanthurids, chae- 

 todontids, and scarids. 



Larger mouthed species such as lutjanids (Stearns 

 1884; Adams and Kendall 1891; Camber 1955; 

 Moseley 1966; Bradley and Bryan 1975; this study), 

 serranids (Moe 1969; Link 1980; Matheson and 

 Huntsman 1984; this study), priacanthids (this 

 study), and scorpaenids (Gotshall 1964) experience 

 oral eversion more frequently than cloacal protru- 

 sion. Fishes with medium-sized mouths and "non- 

 directing" body morphologies (e.g., vermilion snap- 

 per, tomtate, and sparids in this study) exhibit 

 neither type of gut protrusion, instead having a 

 general swelling of the body cavity. 



The relative volume of the swim bladder varies 

 from to 6% of total body volume in marine fishes 

 (Jones 1957). Although measurements were not 



made, the patterns of protrusion in this and other 

 studies (above) suggest that species-specific differ- 

 ences in swim-bladder volume result in varying 

 degrees of internal pressure on ascent. This may 

 contribute to differences in gut protrusion and the 

 extent of body cavity swelling. 



It is not clear why varying rates of ascent would 

 induce varying frequencies of gut protrusion within 

 a fish species. Differences between fish species in 

 the rates at which gases can be resorbed from the 

 swim bladder likely had little effect on patterns of 

 protrusion. Achievement of equilibrium through 

 resorption requires time on the order of hours 

 (Brown 1939; Jones 1951). This is a longer time-scale 

 than the normal vertical movements of most fishes 

 (Steen 1970) and vertical displacements while trawl- 

 ing and angling. Also, the absolute magnitude of 

 swim-bladder expansion is independent of the rate 

 of ascent and should not be considered a factor. Yet, 

 a pattern is apparent in the higher values for angling 

 versus trawl-caught black sea bass and also for red 

 snappers caught with Georgia Bulldog versus Blue 

 Fin trawling gear. Mosely (1966) reported higher 

 oral eversion frequencies for red snappers taken by 

 angling versus those taken while trawling at inter- 

 mediate shelf depths (42-60 m). Bradley and Bryan 

 (1975) also noted for red snappers that angling pro- 

 duced more stomach eversions than trawling, but 

 stated that their data were confounded by differ- 

 ences in the average depths of fishing efforts. Addi- 

 tionally, stomach eversion frequencies for our trawl- 

 caught red snappers (83% taken with "rapid ascent" 

 Georgia Bulldog gear) were 7.5-9.5 times higher 

 than those reported in the literature from similar 

 depths (Fig. 1A; Moseley 1966; Bradley and Bryan 

 1975). It is tempting to attribute these results to dif- 

 ferences in vertical haulback rates. The rate of swim- 

 bladder expansion, linked directly to changes in 

 hydrostasis (Steen 1970) and therefore qualitative- 

 ly more or less "violent", may govern the nature 

 and extent of injuries. 



An additional factor contributing potentially to the 

 types and frequencies of gut protrusion is the con- 

 sistency, amount, and position of prey material in 

 the alimentary tract. Firm material may function 

 as a bonelike directing structure or be what an ex- 

 panding swim bladder acts upon. It is interesting 

 that all of the herniated intestines in planehead file- 

 fish, blue angel fish, and orange filefish contain fecal 

 material. If hydrostatic forces within a fish's body 

 cavity are influenced by gut contents, unequal and 

 variable allocation of sampling effort and catch over 

 a diel feeding cycle could alter estimates of protru- 

 sion frequency for a given fish species. The major- 



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