RICHARDSON ET AL.: EGGS AND LARVAE OF BUTTER SOLE 



Upper jaw length - snout tip to posterior margin 

 of maxillary. 



Illustrations of eggs and larvae were made with 

 the aid of a camera lucida. All specimens had been 

 preserved in 59c Formalin. Illustrations of the 

 caudal fin and skeletal structure were made from 

 cleared and stained specimens. 



VERIFICATION OF 

 IDENTIFICATION 



Reared eggs were fertilized from known par- 

 ents, thus their identity was certain. 



A series of larval specimens from plankton col- 

 lections was linked together by pigment pattern. 

 The left eye had begun to migrate in the largest 

 specimens indicating that they were pleuronec- 

 tids, the only right-eyed flatfishes occurring off 

 Oregon and Washington. Positive identification 

 was based on knowledge of early stages of all but 

 one of the pleuronectids occurring in the area (Ta- 

 ble 1) and on the following meristic characters for 

 /. isolepis (Hart 1973; Ahlstrom^; this study): 



Table l. — Pleuronectid flatfishes occurring off Oregon and 

 Washington with references on early developmental stages. 



Species 



References 



Dorsal fin rays 

 Anal fin rays 

 Abdominal vertebrae 

 Total vertebrae 

 Caudal fin rays 

 Pectoral fin rays 

 Pelvic fin rays 

 Branchiostegal rays 

 Gill rakers 



78-92 



58-69 



9-11, usually 10 



39-42 



17-18, usually 18 



11-13 



6 



7 



4-6 + 7-8 



Additional confirmation was provided by larvae 

 reared to yolk depletion, which were similar to the 

 smallest specimens from the plankton samples. 



DISTINGUISHING FEATURES 



Early and middle stage eggs of/, isolepis are in- 

 distinguishable from those of English sole, Paro- 

 phrys vetulus; starry flounder, Platichthys stella- 

 tus; and sand sole, Psettichthys melanostictus . 

 Chorions of reared eggs are often noticeably stri- 

 ated, but this characteristic is not consistent 

 among reared eggs and is rarely seen in eggs from 

 the plankton. Thus, chorion sculpturing is not use- 

 ful for identifying /. isolepis eggs. 



Atheresthes stomias 

 Embassichthys bathybius 

 Eopsetta lordani 



Glyptocephalus zachirus 

 Hippoglossoides elassodon 



HIppoglossus stenolepis 



Inopsetta ischyra 

 Isopsetta isolepis 

 Lepidopsetta bilineata 



Lyposetta exilis 

 Microstomus pacificus 

 Parophrys vetulus 



Platichthys stellatus 



Pleuronichthys coenosus 



Pleuronichthys decurrens 



Psettichthys melanostictus 



Perlseva-Ostroumova (1960. 1961) 



Richardson (in press) 



Alderdice and Forrester (1971); Ahlstrom (un- 

 publ. data); Richardson (in press) 



Ahlstrom and Moser ( 1 975) 



Dekhnik ( 1 959) ; Pertseva-Ostroumova ( 1 961 ) ; 

 Miller ( 1 969) ; Alderdice and Forrester ( 1 974) 

 Forrester and Alderdice' 



Thompson and Van Cleve (1936): Pertseva- 

 Ostroumova (1961) 



None 



Levings ( 1 968) : Blackburn ( 1 973) 



Pertseva-Ostroumova (1961); Blackburn 

 (1973); Richardson (in press) 



Blackburn ( 1 973) ; Ahlstrom and Moser ( 1 975) 



Hagerman ( 1 952) ; Ahlstrom and Moser ( 1 975) 



Budd (1940)2; Orsi (1968); Blackburn (1973); 

 Ahlstrom and Moser (1975); Misitano (1976) 



Orcutt (1950); Yusa (1957); Pertseva-Ostrou- 

 mova ( 1 961 ) as Pleuronectes stellatus 



Budd (1 940) (as P. decurrens); Sumida et al. 

 (1979) 



Budd (1940) (as P coenosus): Sumida et al. 

 (1979) 



H ickman ( 1 959) ; Sommani ( 1 969) 



^E. H. Ahlstrom, Senior Scientist, Southwest Fisheries 

 Center, National Marine Fisheries Service, NOAA, P.O. Box 



271, La Jolla, CA 92038, unpubl. data. 



'Forrester, C. R., and D. F. Alderdice. 1968. Preliminary observations 

 on the embryonic development of the flathead sole {Hippoglossoides elasso- 

 don)^ Fish. Res. Board Can., Tech. Rep. 100, 20 p. 



^The 6-3 mm larva is not P. vetulus . 



Late stage eggs are readily distinguished from 

 other northeast Pacific pleuronectids with similar 

 size eggs by means of pigment. Embryos in late 

 stage P. melanostictus eggs have scattered yolk-sac 

 melanophores, and those of Platichthys stellatus 

 have pigmented finfolds, while /. isolepis embryos 

 lack pigment in both places. Isopsetta isolepis em- 

 bryos are most similar to those of Parophrys vet- 

 ulus. While /. isolepis embryos usually have sev- 

 eral isolated ventral tail melanophores, their 

 number is quite variable, ranging from none to 

 many, whereas P. vetulus embryos have so many 

 ventral tail melanophores that the pigment ap- 

 pears almost continuous. The head and anterior 

 trunk pigment of/, isolepis is more dendritic and 

 melanophores are less numerous than on P. vet- 

 ulus. Despite these differences, variation in both 

 ventral tail and trunk melanophores, especially in 

 /. isolepis, is so great that late stage eggs of the two 

 species cannot always be reliably separated. 



Most sizes of/, isolepis larvae can be easily dis- 

 tinguished from other flatfish larvae off Oregon 

 and Washington by their body form together with 

 their striking pigment pattern, most notably the 

 three bands of melanophores on the body posterior 

 to the abdominal cavity. After notochord flexion 

 the posteriormost band lines the base of the caudal 

 fin, but the two other bands remain apparent 

 through transformation to benthic juvenile. No 



403 



