LARVAL DEVELOPMENT, DISTRIBUTION, AND ECOLOGY OF COBIA RACHYCENTRON-CANADUM (FAMILY, RACHYCENTRIDAE) IN THE NORTHERN GULF OF MEXICO

Cobia is a highly prized recreational species of worldwide distribution in tropical and subtropical seas, but the development, distribution, and ecology of its early life stages are poorly known. Eggs are spherical, average 1.24 mm in diameter, and have a single oil globule (mean diameter 0.45 mm). The perivitelline space is narrow and the embryo heavily pigmented. Eggs hatch in about 24h at 29-degrees-C based on the relationship between egg diameter and water temperature to predict development time in other marine fishes. Larvae hatch at about 2.5 mm SL. Cobia spawn in both estuarine and shelf waters during the day, arid eggs and larvae are usually collected in the upper meter of the water column. Larvae are recognized by the large supraorbital ridge with a single spine, laterally swollen pterotics, heavy body pigmentation, minute epithelial spicules covering the body integument, and a pair of moderate-to-large, simple spines on either side of the angle of the posterior preoperculum. Only 70 larvae < 20 mm SL were collected and identified from the Gulf of Mexico between 1967 and 1988; most occurred between June and September at surface temperatures greater-than-or-equal-to 25-degrees-C, salinities > 27 parts per thousand, and within the 100 m depth contour. Similar patterns of head spination provide evidence of a sister-group relationship between cobia and dolphinfish rather than that previously hypothesized between cobia and remoras.