series of 34 larvae, we prepared transverse and 

 longitudinal series sections 7 and 10 fim thick 

 (Table 1). The mounted specimens were stained 

 with either Harris's hematoxylin and eosin or a 

 modification of Mallory's connective tissue stain 

 (Martan^). 



Table l. — Number of striped bass larvae sectioned to deter- 

 mine the internal anatomy of the gas bladder and its associated 

 structures. 



Results 



During laboratory aquaria experiments, 

 striped bass larvae were observed with inflated 

 gas bladders as early as day 4. A pestk period of 

 inflation occurred during day 5, closely corre- 

 sponding with the absorption of the yolk sac. 

 Doroshev and Cornacchia (1979) found that 

 striped bass inflated their gas bladder from the 

 5th to the 7th day. 



Striped bass larvae with inflated gas bladders 

 were easily distinguished from larvae with un- 

 inflated gas bladders. Morphologically, the newly 

 inflated gas bladder has the general appearance 

 of a small air bubble, located dorsal to the gut. 

 Behaviorly, larvae that had inflated gas bladders 

 oriented horizontally within the water column 

 and maintained their position without continual 

 swimming motion. Larvae without inflated gas 

 bladders assumed a vertical swimming position, 

 sinking when swimming movements ceased. This 

 characteristic swimming behavior of larvae with 

 noninflated gas bladders was defined as "swim- 

 up" behavior. 



In 4.8-day-old striped bass larvae, the nonin- 

 flated gas bladder primordium was dorsal and 

 slightly posterior to the jimction of the esophagus 

 and the stomach. The stomach was at the right of 

 the dorsomedial gas bladder primordium. The 

 walls of the noninflated gas bladder primordium 

 were much thicker ventrally than either dorsally 



^Martan, J. 1968. Laboratory instructions: Histological 

 techniques in zoology. South. 111. Univ., Carbondale, 98 p. 



or laterally. Columnar epithelium comprised the 

 ventral mass of the gas bladder primordium. The 

 noninflated gas bladder possessed a slight, dor- 

 sally located lumen. An open pneumatic duct 

 connected the foregut with the right side of the 

 posterior wall of the gas bladder primordium. The 

 duct was composed of a single layer of cuboidal 

 epithelium, surrounded by a layer of connective 

 tissue. 



A network of arterioles and venules, a 

 rudimentary rete mirabile, ran parallel and ven- 

 tral to the noninflated gas bladder primordium. At 

 the posterior end of the gas bladder, the rete ar- 

 terioles and venules turned dorsoanteriorally and 

 entered a layer of loose connective tissue adjacent 

 to the ventral columnar epithelium of the gas 

 bladder. Within this connective tissue, a network 

 of capillaries connected the arterioles and ven- 

 ules. Since the rete mirabile proceeded directly to 

 the secretory epithelium of the gas bladder, the 

 whole structure may properly be called a gas 

 gland (Steen 1970). A gas gland is formed in 

 striped bass before the initial inflation of the gas 

 bladder. 



In older (8 days) striped bass larvae that still 

 had a noninflated gas bladder, the capillary net- 

 work was more developed and pushed closer to 

 the ventral columnar epithelium of the gas blad- 

 der. This gave the epithelium a festooned appear- 

 ance. 



In striped bass larvae that were in the process 

 of inflating their gas bladders, the initial infla- 

 tion occurred at the anterior end of the gas blad- 

 der. The columnar epithelium, which previously 

 had dominated the ventral wall of the gas blad- 

 der, became confined to the posterior portion of 

 the gas bladder as inflation progressed. At no 

 time were distinct vacuoles visible within the 

 ventral, columnar epithelium. 



In 5.5-day-old striped bass larvae that pos- 

 sessed an inflated gas bladder, the ventral 

 epithelium was reduced to cuboidal epithelium 

 and was restricted to the posteriorventrad portion 

 of the gas bladder where it was in close association 

 with the gas gland. The remaining walls of the 

 inflated gas bladder were composed of stretched 

 epithelium. The rete mirabile still ran parallel 

 and ventral to the newly inflated gas bladder. 

 Capillaries of the rete mirabile made contact with 

 secretory epithelium towards the posterior of the 

 gas bladder. 



In all striped bass larvae which were 4.3-5.5 

 days old and possessed an inflated gas bladder, a 



1001 



