Chemotactic Response Of Fish Macrophages To Legionella-Pneumophila - Correlation With Pathogenicity

MD MURPHY
ME CHITTENDEN

Abstract

Collections were made for gulf butterfish Peprilus burti along a cross-shelf transect at depths of 5-100 m in the Gulf of Mexico off Texas from October 1977 to July 1980. Butterfish mature at 100-160 mm fork length as they approach age I. Spawning occurs primarily from September through May, but length frequencies indicate it concentrates, or is most successful, in distinct "Winter" (late January-mid-May) and "Fall" (early September-late October) periods that coincide with downcoast, alongshore currents (toward Mexico). Gonad data and persistence of small fish indicate spawning in winter, but at a low level. Spawning probably occurs offshore and upcoast toward the northcentral Gulf. Surface currents of the cyclonic shelf gyre probably transport eggs/larvae inshore and downcoast to recruit to the bottom in water 5-27 m deep, used as nurseries by butterfish when they are 2-5 months old. Butterfish disperse offshore as they mature and congregate in 36-100 m depths when they are 9-12 months old. They average 130-146 mm in fork length at age I in the northwestern Gulf, but 120-124 mm at age I and about 170 mm at age II in the northcentral Gulf. Estimates for the von Bertalanffy growth parameters L-infinity, K, and t0 were 164 mm, 1.99/year, and -0.20 years, respectively, for pooled northwestern Gulf Winter cohorts and 141 mm, 2.69/year, and -0.06 years, respectively, for pooled Fall cohorts. Somatic growth ceases as spawning approaches in the northwestern Gulf, but fish from the northcentral Gulf show large annual size increments. Butterfish reach about 200 mm in fork length, the largest ones occurring in the northcentral Gulf. Apparent maximum ages are 1-1.5 years in the northwestern Gulf, and 2-2.5 years in the northcentral Gulf. Differences in population attributes suggest complete mortality at age I in the northwestern Gulf or some unknown combination of an offshore and permanent contranatant spawning or postspawning emigration of adults to the northcentral Gulf. The genus Peprilus shows zoogeographic differences in population dynamics near Cape Hatteras, North Carolina.