EGGS AND LARVAE OF BUTTER SOLE, ISOPSETTA ISOLEPIS (PLEURONECTIDAE), OFF OREGON AND WASHINGTON

Development ofbutter sole, Isopsetta isolepis, is described from egg through benthic juvenile, based on reared and field-collected specimens. Isopsetta isolepis eggs are planktonic, spherical, and transparent with a narrow perivitelline space, homogeneous yolk, and no oil globule. Diameters of80 reared eggs averaged 0.93 mm(range 0.90-0.99 mm). Using light microscopy, early and middle stage eggs are indistinguishable from those of three other pleuronectids, English sole, Parophrysvetulus, sand sole, Psettichthys melanostictus,and starry flounder, Platichthys stellatus, with which they cooccur. Pigment patterns distinguish late stage I. isolepis eggs from those of Psettichthysmelanostictus and Platichthys stellatus. Because the late stages ofI. isolepis embryosvary widely in degree and character ofpigmentation,they often cannot be reliably separated from those of Parophrys vetulus. Larvae are readily distinguished by three bands of melanistic pigment on the tail region of the body combined with myomere counts (39-42). Transformation from larva to juvenile takes place at about 18-23 mm. Larvae are abundant in nearshore coastal waters off Oregon and Washington in winter and spring, where they cooccur with larvae of P. vetulus. Recently transformed benthic juveniles of 1. isolepis usually are found offshore rather than in the bay and nearshore habitats occupied by young juvenile P. vetulus.