Abstract
The problem of whether the anadromousAlosa mediocris spawns in fresh water or at sea is clarified; eggs stripped from brood fish taken during May 1956 in tidal fresh water in the Patuxent River, Maryland, were hatched successfully in fresh water. Unknown eggs and larvae taken in plankton samples at the same site in 1953 where adults are abundant were also believed to be this species. Data and illustrations of the eggs and early larval stages of this species are presented for the first time. Very young transforming stages between 9–20 mm are tentatively identified from upper tidewater plankton cllections. Some juvenileA. mediocris, taken by beach seine and trawls, are treated in detail. All are compared briefly with closely related clupeoids found under similar ecological conditions. The egg is spherical, transparent, slightly adhesive, and midway in diameter ( $${\text{x}}$$ =1.49 range, 1.34–1.64) between the American shad,A. sapidissima, and branch herrings,A. pseudoharengus andA. aestivalis. It is semi-demersal, and partially buoyant only under moving water conditions. The granular yolk is light amber yellow ( $${\text{x}}$$ =0.98mm in diameter), and has no oil globule. Prolarvae hatch in two or three days between 65 and 70°F ( $${\text{x}}$$ =6.1 mm, range, 5.2–6.5. mm T.L.). They are slender and transparent with a granulated yolk sac, unpigmented eyes, and sparse body pigmentation. When the larvae are about 6.5 mm and three days old, the yolk sac is assimilated and advanced development of the bone structure and visceral organis occurs. The body pigmentation is restricted to the dorso-lateral edge of the gut and on the caudal area. Postlarvae transform to juveniles between 10 and 35 mm when: the fins develop, most of the adult meristic numbers are attained, more intensive pigmentation occurs, and the young clupeoid form is developed. Squamation and scutalation begins between 30 and 35 mm. The myotome count in the young between 20 and 30 mm corresponds to the adult vertebral number of 54. The remarkable paucity of juveniles from estuarine collections is discussed. A hypothetical growth rate, derived from existing limited data, suggests that young-of-the-year growth exceeds that of juveniles of other species ofAlosa. Observations of the adults on the spawning grounds indicate that spawning reaches a peak in early May and ends in early June. Males average 14.1 inches T.L. (range, 11.3–16.3), while females average 14.8″ (12.6–17.8). Commercial production has declined markedly during the last seven decades, but the hickory shad has never been economically valuable. It has assumed great importance as a game fish in recent years.
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