COMPARATIVE EARLY-LIFE HISTORIES OF WESTERN ATLANTIC SQUIRRELFISHES (HOLOCENTRIDAE) - AGE AND SETTLEMENT OF RHYNCHICHTHYS, MEEKI, AND JUVENILE STAGES

Fishes of the family Holocentridae have a morphologically distinctive postlarval ''rhynchichthys'' stage characterized by extensive head spi nation, including a prominent serrate rostral spine. In most species t he rhynchichthys physiognomy persists until settlement, which occurs w ithin a size range of about 30-50 mm SL. The two species of Holocentru s have a uniquely protracted pelagic period during which they transfor m from the rhynchichthys at about 40 mm SL to a distinctive, unornamen ted, and relatively streamlined prejuvenile ''meeki'' stage that may r each 74 mm SL prior to settlement. Analysis of daily growth increments in lapilli of recently settled juvenile and adult holocentrids confir ms that the pelagic stages of H. ascensionis and H. rufus grow more ra pidly and settle at significantly greater ages and larger sizes than o ther holocentrids. A microstructural transition zone in the otoliths o f these two species probably corresponds to the rhynchichthys-meeki mo rphological transformation of these pelagic stages. In other holocentr ids examined a similar microstructural transition corresponds to the r hynchichthys-juvenile morphological transformation associated with set tlement onto reefs. The average age and size of small juveniles of H. rufus collected at their earliest appearance during censuses of shallo w reefs was 67 days and 66 mm SL, but the average pretransition increm ents in their lapilli was only 44. Limited data for H. ascensionis are similar, but differ in average age (59 days) and size (56 mm SL) at s ettlement and number of pretransition increments (48). The size of spe cimens found in museum collections also substantiates that H. rufus is larger at settlement (and has a larger maximum size meeki stage) than H. ascensionis. The two meeki stage specimens for which we have otoli th data (for H. rufus, both slightly less than 50 mm SL) lack the expe cted transition mark. However, their ages at capture (38 and 43 days) suggest that they are newly transformed from the rhynchichthys stage, and marginal transition marks are difficult to identify. Daily growth increments were validated in one meeki stage H. rufus and two rhynchic hthys stage Sargocentron coruscus that were maintained, respectively, for five and nine days in aquaria after strontium infusion of their ot oliths. The rapid morphological transformation of the meeki stage into a benthic juvenile within two days of capture, including overnight ch ange in coloration from blue above and silver below to orangish red wi th pale stripes, is described.