HORN: SWIM-BLADDER STATE AND STRUCTURE 



in Hyperoglyphe. Retial orientation was generally 

 parallel to the long axis of the bladder, and the 

 retial bundle either remained single anteriorly as 

 in Icichthys (Figure IJ) or variously branched into 

 smaller bundles perpendicular to the long axis as 

 in Hyperoglyphe (Figure IK). The rete bundle of 

 Schedophilus had a sharp turn near the posterior 

 end producing a sigmoid outline (Figure IF). 

 Swim-bladder shape which depends to a large de- 

 gree upon secretory and absorptive states varied 

 from elongate with a large posterior chamber to 

 short and bulbous with either a small posterior 

 chamber or no posterior chamber visible. 



Stromateidae 



The organ was similar in structure and shape to 

 that of the Centrolophidae. The gas gland cells of 

 Peprilus triacanthus were small (6-10 /jm) and 

 were arranged in loops and rings (Figure 5). In one 

 P. triacanthus (16.5 mm SL) the retial blood ves- 

 sels formed a single bundle posteriorly which ex- 

 panded anteriorly over the gas gland whereas in 

 two somewhat larger juveniles (22.2 and 33.9 mm 

 SL) the retia were more nearly perpendicular to 

 the long axis of the bladder and consisted of 7 or 

 8 distinct branches. 



Amarsipidae 



The swim bladder was similar to that of the 

 Centrolophidae. The rete originated posteriorly as 

 a single bundle and divided anteriorly into 7 or 8 

 distinct branches before entering the gas gland. 



Nomeidae 



Swim-bladder volume ranged from 0.7% in 

 Nomeus to 3.3% of body volume in Cubiceps and 

 gas gland size from 10-30 ;u m in Nomeus to 25-40 

 /L( m in Cubiceps and Psenes. Retial length varied 

 from 0.4 mm in Nomeus to 1.9 mm in Cubiceps. 

 The retia were divided into several branches and 

 in position were more nearly perpendicular than 

 parallel to the long axis of the bladder (Figure IE, 

 H). Small juvenile Psenes cyanophrys (9.1 and 

 14.1 mm SL) had retia almost parallel to the long 

 axis of the bladder (Figure IG) whereas larger 

 juveniles (e.g., 60.8 mm SL) tended to have retia 

 which were more nearly perpendicular to the long 

 axis and more highly branched. The pattern, seen 

 also in Peprilus triacanthus , may be part of the re- 

 gression process that the swim bladder undergoes. 



Tetragonuridae 



The sac was small (0.6% of body volume) and 

 elongate. The retial bundle was parallel to the 

 long axis of the bladder and, as in Schedophilus 

 medusophagus , had an S-shaped turn near the 

 posterior end (Figure IC). The gas gland was rela- 

 tively small and located at the anterior end of the 

 lumen. 



Ariommidae 



The swim bladder was relatively large (up to 

 2.9% of body volume) and elongate. The gas gland 

 cells were in the upper range of size (20-46 ;u m) 

 among the stromateoids examined, and the retia 

 were broad, fanlike and perpendicular to the long 

 axis of the bladder (Figure lA). 



Size at Swim-Bladder Inflation 



The swim bladder becomes functional early in 

 the life of stromateoids. Whether the larval fishes 

 gulp air at the surface or whether gas is secreted to 

 initially fill the bladder was not determined. 

 Examination of larvae of four genera indicated 

 that the organ in one species was almost 

 completely developed at 3.0 mm SL and in three 

 others at slightly larger sizes. Specimens of 

 Peprilus simillimus as small as 3.0 mm SL had 

 what appeared to be a fully developed swim 

 bladder whereas in smaller individuals, e.g., 2.7 

 mm SL, the sac was inflated but the gas gland and 

 retia were incomplete. The bladder was absent in 

 a fish of 2.4 mm SL. Aseriesof larvae, 3.4-5.0 mm 

 SL, of an unidentified species of Psenes had an 

 inflated swim bladder, and larvae ofTetragonurus 

 cuvieri as small as 4.0 mm SL had a gas-filled sac 

 which was visible through the semitransparent 

 body wall. Individuals of Icichthys lockingtoni, 5.0 

 and 7.5 mm SL, had an inflated sac and an 

 apparently fully developed gas gland and retial 

 complement. 



Swim-Bladder Regression 



The swim bladder regresses, becomes nonfunc- 

 tional, and finally disappears before the adult 

 stage is reached in all stromateoid genera except 

 Pampus in which the organ is apparently absent 

 and possibly Nomeus in which the largest 

 individual examined (142.7 mm SL) had a 

 functional swim bladder. The regression is a 



101 



