FISHERY BULLETIN: VOL. 72, NO. 4 



MATERIALS AND METHODS 



Eggs that were used for descriptive purposes 

 were collected in 1971 and 1972 during ichthyo- 

 plankton surveys in the eastern Gulf of Mexico. 

 Twenty-three eggs in varying stages of develop- 

 ment were examined and measured. Eggs from 

 the laboratory rearing experiment were lost and 

 consequently could not be described. 



We selected only the best specimens for this 

 study by eliminating fish with pronounced body 

 curvature and those in poor condition. We used 

 53 of the 197 available specimens. Forty-two of 

 these specimens were measured with an ocular 

 micrometer of a dissecting microscope to provide 

 data on body proportions. Seventeen of the speci- 

 mens were cleared and stained to provide meristic 

 data and osteological data. Specimens shown in 

 the illustrations were among those cleared and 

 stained for verification of the fin-ray counts. 

 Staining procedures followed those of Taylor 

 (1967). 



During development, O. oglinum undergoes 

 some pronounced changes in structure. These 

 changes are difficult to adequately define, par- 

 ticularly the metamorphic stages. We have fol- 

 lowed the definitions used by Moser and Ahlstrom 

 (1970), and we have also taken into account 

 Ahlstrom's (1968) comments on the subject. Our 

 yolk-sac larvae were lost, so our description 

 commences with the larval period. The period 

 between the larval period and juvenile period 

 is termed the transitional stage, following Moser 

 and Ahlstrom (1970). At the beginning of the 

 transitional period (about 15 mm standard 

 length), the animals commence metamorphosis 

 into juveniles. 



Our methods of counting and measuring closely 

 follow Moser and Ahlstrom, but for convenience 

 are defined as follows: 



Body length — In early stage larvae and in 

 those undergoing notochord flexion, the body 

 length is the distance from the tip of the snout 

 to the tip of the notochord. After the hypural 

 complex is developed the standard length mea- 

 surement is used, i.e., the distance from the tip 

 of the snout to the posterior margin of the hypural 

 elements. While the notochord is undergoing 

 flexion and the hypural elements are developing, 

 this estimated standard length measurement is 

 denoted in the tables. 



Eye diameter — Maximum width of the pig- 

 mented eye measured on the horizontal axis. 

 Snout length — Distance from the tip of the 

 snout to the anterior edge of the orbit. 



Head length — Distance from the tip of the snout 

 to the posterior edge of the opercle. 



Length of dorsal and anal fin bases — Distance 

 from the origin of the first ray to the point 

 where the posterior part of the last ray con- 

 tacts the body. 



Snout to origin of dorsal fin — Identical to the 

 predorsal length defined by Hubbs and Lagler 

 (1958). 



Snout to origin of pelvic fin — Distance from the 

 tip of the snout to the pelvic fin base. 



Snout to origin of anal fin — Distance from the 

 tip of the snout to the origin of the anal fin 

 (in small larvae, before the anal fin develops, 

 this measurement is defined as the distance from 

 the tip of the snout to the end of the gut; it can 

 be used as gut length for all larvae and small 

 juveniles). 



Origin of dorsal fin to base of caudal rays — 

 Distance from origin of the dorsal fin to the end 

 of the hypural plate. 



Body depth — Vertical depth of the body mea- 

 sured at the origin of the pelvic fins (in larvae 

 that have not developed pelvic fins, the mid- 

 point of the body is used). 



Origin of anal fin to base of caudal rays — Dis- 

 tance from ori^n of the anal fin to the end of 

 the hypural plate. 



Origin of pelvic fin to base of caudal rays — 

 Distance from origin of the pelvic fin to the end 

 of the hypural plate. 



DESCRIPTION OF THE EGGS 



Twenty-three eggs ranged from 1.10 to 1.28 mm 

 in diameter (mean = 1.19 mm). The chorion 

 is thin and fragile, unsculptured, and unpig- 

 mented. A single oil globule is present, ranging 

 from 0.12 to 0.16 mm in diameter (mean = 0.15 

 mm). As in most clupeid eggs, the perivitelline 

 space is wide, and the yolk mass is vaguely 

 segmented. For 10 embryos at the blastodisc 

 stage the yolk diameter averaged 59% of the 

 egg diameter, while for 13 advanced embryos 

 the yolk diameter averaged only 539^ of the egg 

 diameter. A paired dorsolateral series of tiny 

 melanophores is present on embryos that are 

 about to hatch (Figure 1). Opisthonema eggs 



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