AHLSTROM: FISH LARVAE IN EASTERN TROPICAL PACIFIC 



stations located between lat 6° and 2° N along 

 long 92° W. 



Louieina rara (Lutken) (43 occurrences, 56 

 larvae ) 



The larger larvae of Loweina rara are among 

 the most elegant of myctophid larvae. Larvae 

 of this species were rather uncommon in the 

 EASTROPAC area, although widely distributed. 

 Larvae were taken most frequently, however, in 

 the vicinity of the equator, between ca. lat 8° N 

 and 7° S; 36 of the 43 occurrences were in the 

 equatorial zone. The largest collection of Lo- 

 weina larvae was only four specimens, and only 

 a single specimen was obtained in most collec- 

 tions (i.e., in 35 of 43). The distribution of 

 larvae of L. rara on EASTROPAC I is illus- 

 trated in Moser and Ahlstrom (1970). 



Myctophutn spp. ( 187 occurrences, 1,393 larvae) 



Myctophiim is one of the more abundant gen- 

 era represented in the eastern tropical Pacific. 

 Juvenile and adults of five species were ob- 

 tained in 1-m plankton hauls and micronekton 

 net hauls: Myctophum atirolaternatum Gar- 

 man, M. asperum Richardson, M. hrachygnathos 

 (Bleeker), M. lychnobium Bolin, and M. nitid- 

 ulum Garman. Body form and pigmentation of 

 the five of six kinds of Myctophum larvae taken 

 in EASTROPAC I are as diverse as has been 

 observed within a myctophid genus. Larvae of 

 M. nitiduliini, described by Moser and Ahlstrom 

 (1970), are broad headed and deep bodied with 

 eyes on short stalks; larger larvae of this spe- 

 cies are among the most heavily pigmented 

 myctophid larvae. 



A quite different developmental pattern is dis- 

 played by larvae of M. asperum and M. hrachyg- 

 nathos. The larvae of these species are also 

 deep bodied and big headed, but the eyes are 

 not borne on stalks. The most characteristic 

 feature of the development of these larvae is 

 the early appearance of Dn photophores which 

 form on larvae between 4.0 to 5.0 mm in length, 

 soon after the appearance of the Bra photo- 

 phores. Larvae of M. asperum develop large 

 characteristic melanophores (Pertseva-Ostrou- 



mova, 1964), but larvae of M. hrachygnathos 

 are only slightly pigmented. 



Larvae of M. lychnobium also are but lightly 

 pigmented; they are much more slender and 

 elongated than larvae of M. hrachygnathos and 

 do not develop the Dn photophores early. A 

 notable feature is the marked length of the tear- 

 drop (choroid) tissue that develops under the 

 eyes (as long as in Gonichthys or Centrobranchus 

 larvae). 



The extraordinary larvae of M. aurolatema- 

 tum were only recently recognized and are not 

 included in the above counts of Myctophum. 



Notolychnus valdiviae (Brauer) (158 

 occurrences, 868 larvae ) 



This is probably the smallest species of myc- 

 tophid, and cei'tainly one of the most widespread 

 in offshore, oceanic waters. The larvae seldom 

 occur in large numbers (average number per 

 positive haul was 5.5 larvae). They were 

 present in about one-third of the collections 

 made on EASTROPAC I, although most occur- 

 rences were farther offshore than 300 miles of 

 the coast (Fig. 11). Juvenile and adult A'', val- 

 diviae were frequently taken in the oblique 

 plankton hauls. Perhaps as many juvenile and 

 adult specimens of N. valdiviae were obtained 

 by this means as of all other myctophids com- 

 bined. Since this species has only a middling 

 rank with regard to abundance of larvae, the 

 frequency of capture of adults is probably less 

 a measure of abundance than of their shallow 

 depth distribution and poor swimming ability. 



Notoscopelus resplendens (Richardson) 

 (70 occurrences, 283 larvae) 



This is the species of Notoscopelus known to 

 occur in the eastern Pacific. On EASTROPAC, 

 Notoscopebis larvae were taken more frequently 

 and in larger numbers in the equatorial zone 

 between lat 5° N and 5° S (40 occurrences, 209 

 larvae). 



Protomyctophum sp. ( 36 occurrences, 78 larvae ) 



All occurrences of Protomyctophum larvae, 

 except one, were between lat 10° N and 5° S. 



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