HOUDE: NORTHERN SENNET 



rays first develop. A complete study of osteology 

 was not undertaken, but development of teeth 

 and caudal skeleton were examined in detail. 



DEVELOPMENT 



EMBRYO 



Two preserved eggs of S. horealis were 1.22 

 and 1.24 mm diameter. They had single, clear 

 yellow oil globules 0.27 and 0.29 mm diameter. 

 The perivitelline space was narrow and the 

 transparent yolk was vaguely segmented. In 

 eggs that I preserved about 2 hr after collection, 

 the embryo was not well developed and no pig- 

 ment was visible (Figure lA). Later stage 

 embryos developed both melanophores and 

 xanthophores on the body, giving the living em- 

 bryo a greenish appearance to the naked eye. 

 The eggs hatched about 20 hr after collection 

 at an incubation temperature of 24° C. 



MORPHOLOGY OF LARVAE 

 AND JUVENILES 



Larvae of S. horealis were 2.6 mm SL at hatch- 

 ing and were robust due to the large yolk sac 

 (Figure IB) but became characteristically 

 slender after its absorption (Figures 2 and 3). 

 Body depth averaged 12 9r SL for larvae from 

 immediately after yolk absorption to juveniles 

 of 21.0 mm SL. Gut length was moderately long 

 in S. horealis larvae. Jaws were not elongated 

 on newly hatched larvae but became so shortly 

 after the yolk sac was absorbed and mouth parts 

 became functional. Growth in length of labor- 

 atory-reared larvae is given in Figure 4. 



Yolk Absorption 



The yolk sac was large and nearly spherical 

 at hatching, with its oil globule at the anterior 

 end (Figure IB) . Some yolk and the oil globule 

 remained up to 4 days after hatching (Figures 

 2 A and 2B). Feeding began shortly before the 

 yolk was completely absorbed. 



Head Length 



The head of recently hatched S. horealis was 

 short (Figures 1 and 2), but increased rapidly 

 in length as larvae developed. Head length in- 

 creased relative to body length from 13% SL 

 for newly hatched larvae to a constant value of 

 about 33% SL for larvae 9 mm SL and longer 

 (Table 1). Over half the head length increase 

 was related to an increase in length of the snout 

 during development. 



Snout Length 



Snout length increased on developing larvae 

 from about 3% SL 1 day after hatching to a 

 value of about 12% SL at 9 mm and gradually 

 to 14% SL for juveniles (Table 1). 



Tip of Lower Jaw 



A fleshy tip began to develop on the lower jaw 

 at about 5.0 mm SL (Table 1). Its relative 

 length increased from less than 1 % SL to about 

 3% SL when larvae had grown to 14.5 mm SL 

 (Figures 2 and 3). The structure ranged from 

 3 to 6% SL on 17 to 30 mm SL wild-caught spec- 

 imens. On two juveniles, 59.6 and 62.9 mm SL, 

 the length of the fleshy tip was only 3% SL. The 

 length of this structure on both laboratory- 

 reared and wild-caught specimens varied rather 

 markedly. 



Jaws and Teeth 



The mouth was not developed until larvae 

 were 4.0 mm SL, about 3 days after hatching 

 (Figure 2B). Teeth first appeared on the pre- 

 maxillary bones at 5.3 mm SL when the jaws 

 became barracuda-like (Figures 2C and 2D). 

 Initially, the teeth appeared bluntly conical but 

 became caninelike when larvae grew to 7.0 mm 

 SL. Teeth were developed on the lower jaw and 

 were developing on the palatine bones at 7.4 mm 

 SL. The palatine bones on larvae longer than 

 12 mm SL bore the largest teeth, except for the 

 second and third pairs of premaxillary teeth; 

 these were long and directed posteriorly. All 



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