648 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Table 173. Summary of Ontogenetic Characters of Pleuronectiforms. (Line indicates data unavailable or presented elsewhere in column.) 



• Single oil globule present in 3 speeies- 



** 0-2 in EtropiLi, 0. 2. 3 in Cnhanchthys; 5-8 in Syactum: 8-1 1 in Cyclopsena. 

 ••* Third ray elongated in Achirus. 



■••• 0. I. or 2 in Cithanchthy^. 2 or 3 in Cyclopsetta and Syacium: or I in Etropus. 

 •*••* S Iti^tlata develops elongate third and fourth rays, 

 ****** Protruding in Chascanupsetta. Petecanichthys. and Kamuharaia. 



species in other groups, including Soleidae, Cynoglossidae, 

 Paralichthyidae, and Bothidae. 



With a few exceptions, the eggs of flatfishes are pelagic, round, 

 have homogeneous yolk, a narrow perivitelline space, and an 

 unsculptured chorion (Fig. 341). The eggs of all flatfishes are 

 spawned separately. The characters of eggs showing greatest 

 differences among flatfishes are 1) egg size, and 2) the presence 

 or absence of an oil globule(s) (Tables 170-172). 



Of the approximately 60 species of pleuronectine flatfishes of 

 the North Pacific and North Atlantic, eggs are known for at least 

 45 (Table 170). Six species are known to have demersal eggs; 

 these are round or occasionally off-round and have a sticky, 

 adhesive chorion that permits clustering or adhesion to bottom 

 objects. Egg diameters range from 0.66 to 4.5 mm within the 

 subfamily. The yolk is homogeneous in all pleuronectine eggs. 

 The perivitelhne space is narrow to moderate, except for eggs 

 of Hippoglossoides, which have a wide perivitelline space, usu- 

 ally 25-30% of the egg diameter on either side of the yolk mass. 

 The chorion has the appearance of being smooth on eggs of most 

 species, but closer inspection reveals striations or reticulations 

 on the chorion of some kinds. The chorion of Pleuromchthys 

 eggs has a striking hexagonal pattern. The eggs of pleuronectine 

 flatfishes, except for three species, lack an oil globule. The state 

 of embryonic development achieved in the egg is related to egg 

 size, more specifically to yolk size. Larvae hatching from small 

 eggs lack eye pigment, a functional mouth and pectoral fins; 

 those hatching from larger eggs are much more advanced, with 

 pigmented eyes, a functional mouth and pectorals. Embryos in 



middle- and late-stage eggs are pigmented, with patterns varying 

 between genera and species. Among species, yolk pigment can 

 range from unpigmented, to some pigment on yolk adjacent to 

 the embryo, to heavily pigmented. Pigment can also be present 

 on finfolds of late-stage eggs of some flatfishes. 



Eggs of Scophthalmidae. Paralichthyidae and Bothidae have 

 a single, small to moderate-sized oil globule, are pelagic, round, 

 have a narrow to moderate perivitelline space, and homoge- 

 neous yolk (Fig. 341, Table 171). In late-stage eggs and newly 

 hatched larvae the single oil globule usually is in the rear of the 

 yolk mass. 



Eggs are known for 8 of the 10 species of scophthalmid flat- 

 fishes. They range in size from 0.72 to 1.50 mm. The chorion 

 is striated or rugose in six species and this may apply to all. 

 Embryos develop considerable pigment over the head and body 

 and often in finfolds; pigment over the yolk mass and oil globule 

 can range from none, or sparse, to intense. 



Eggs are known for only a few species in the family Paralich- 

 thyidae. These range in size from 0.70-1.38 mm; chorions are 

 unsculptured. Except for a few species of Arnoglossus. eggs of 

 bothid flatfishes are practically unknown. Mito (1963) lists 10 

 kinds of bothid eggs oflT Japan, unidentified to genus; 8 of these 

 have diameters under 1.0 mm. Eggs of his Bothidae No. 9 are 

 slightly ofl"-round and three different eggs have a conspicuous 

 wart-like appendage. Much work remains to be done in iden- 

 tifying eggs of fishes of these families, preferably through rearing 

 eggs from known parents. 



Eggs with multiple oil globules are typical of the families 



