A RE-DESCRIPTION OF ATLANTIC SPADEFISH LARVAE, CHAETODIPTERUS-FABER (FAMILY, EPHIPPIDAE), AND THEIR DISTRIBUTION, ABUNDANCE, AND SEASONAL OCCURRENCE IN THE NORTHERN GULF-OF-MEXICO

The Atlantic spadefish (Chaetodipterus faber) is the only member of th e family Ephippidae in the western Atlantic Ocean and its life history is poorly understood. We redescribe Atlantic spadefish larvae, discus s their relationship to known larvae of other ephippid genera, and dis cuss the distribution, abundance, and seasonal occurrence of Atlantic spadefish in the northern Gulf of Mexico. Larval Atlantic spadefish ar e characterized by a small, peak-like, median supraoccipital crest wit h a single, dorsally directed spine; large preopercle spines, numerous serrate ridges, and other spines on the head; a deep, robust body whi ch becomes laterally compressed; heavy body pigmentation; and early de velopment of specialized spinous scales or ''prescales'' (at about 5.5 -mm standard length [SL]). Transition to juvenile stage begins about 8 .0-8.5 mm SL. Developmental morphology and head spination of Atlantic spadefish is similar to that of Pacific spadefish, Chaetodipterus zona tus. Sequence of fin completion is pelvics - dorsal and anal soft rays - dorsal spines-pectorals. Overall, greater-than-or-equal-to 85% of A tlantic spadefish larvae were found in waters greater-than-or-equal-to 28.0-degrees-C and between 26.7 and 31.3 ppt. Larvae occur primarily in coastal waters, except near the Mississippi River delta, an area wi th a narrow shelf and rapidly increasing water depths. Delta waters ma y offer additional habitat suitable to Atlantic spadefish larvae becau se of lower salinities. Larvae are primarily collected between June an d August and in the north-central Gulf of Mexico. Larval Atlantic spad efish are apparently rare in the eastern Gulf off Florida. Catch rates near the Mississippi River delta during August were higher than elsew here in the north-central Gulf and suggest a possible association with riverine frontal areas which requires further study.