Decapterus

Abstract: The diel reproductive periodicity of Carangidae is poorly known but appears to be highly variable between species. Some species spawn during the day, others are believed to spawn at night, and it is demonstrated here that round scad, Decapterus punctatus, spawn at dusk. We collected D. punctatus in the eastern Gulf of Mexico during three April cruises (1995, 1996, and 1997). Based on histological criteria, size at 50% maturity was 113 mm fork length (FL) for males and 128 mm FL for females. The gonad-somatic index (GSI) of mature males was significantly different between hours and appeared to show diel periodicity. Diel periodicity was also observed in changes in female GSIs, whole oocyte diameters, and ovarian histology. The average GSI of mature females fluctuated two-fold between day and night, and the size distribution of whole oocytes in some fish was bimodal (at 0.3–0.4 and 0.7–0.8 mm diameter) at dusk rather than unimodal during most of the diel cycle. Histological preparations revealed that these rapid changes in ovarian GSIs and oocyte size distributions were the result of final oocyte maturation. Germinal vesicle migration was observed from 0900 to 1400 hours eastern standard time (EST), germinal vesicle breakdown was evident as early as 1100 hours EST, and ovulation occurred as early as 1800 hours EST. Spawning frequency (approximately every 5 days) was similar whether calculated from the proportion of females with hydrated oocytes during the afternoon or from the proportion of females with postovulatory follicles during the morning. Batch fecundity correlated with fish size and ranged from 5,500 to 34,700 hydrated eggs per individual. These findings do not support published hypotheses that young-of-the-year D. punctatus reproduce before their first winter or that D. punctatus reproductive output is bimodal within a year.

Abstract: The diel, lunar, and seasonal timing of spawning in Atlantic goliath grouper Epinephelus itajara (Lichtenstein, 1822) in the United States is highly specific, occurring at night during new moon phases of August, September, and October. We derive these patterns from four lines of evidence apparent on spawning sites during the known spawning season: (1) from the transitory appearance of fish aggregations; (2) from simultaneous recordings of goliath grouper nighttime calls and nighttime vertical ascents that were far more frequent during the new moon phase than on the full moon; (3) from collections of goliath grouper eggs (genetically verified) at night downstream from known spawning sites; and (4) from significantly higher frequencies of both hydrated oocytes (indicating imminent spawning) and postovulatory follicles (indicating recent spawning) in ovarian biopsies taken from goliath grouper captured on spawning sites during new moon phases relative to full moon phases. We suggest that dark-night spawning is an adaptation minimizing egg predation by several species of scad [Decapterus punctatus (Cuvier,1829), Decapterus tabl Berry,1968, and Decapterus macarellus (Cuvier,1833)] and herring [Sardinella aurita Valenciennes,1847 and Etrumeus teres (DeKay,1842)] that are abundant on goliath grouper spawning sites.The seasonal spawning of goliath grouper, late summer–early fall, coincides with habitat conditions considered ideal for settlement of early juveniles in mangrove nurseries.

Abstract: We examined 1,825 bongo-net samples collected during Southeast Area Monitoring and Assessment Program (SEAMAP) ichthyoplankton surveys of United States Gulf of Mexico waters (1982–1986) for carangid larvae. Objectives were to describe the distribution of carangid larvae and to examine distribution patterns relative to areas of higher zooplankton volumes in order to reveal areas that may be important nurseries. Samples contained about 29,200 carangid larvae from 13 species or species complexes in 11 genera. Chloroscombrus chrysurus and Decapterus punctatus accounted for 91.7% of all larvae. We found that the ‘scads’ (D. punctatus, Trachurus lathami, and Selar crumenophthalmus) utilize temporally and/or spatially distinct spawning strategies to reduce co-occurrence of larvae. Samples contained fewer larvae than expected of the amberjacks (Seriola spp.), Caranx crysos, and C. hippos/latus given the abundance of adults in the survey area, possibly due to inadequate sampling at appropriate times and locations, gear avoidance, or gear bias. Zooplankton displacement volumes (ZDVs) differed among regions and seasons and were inversely related to surface salinity and station depth. Differences among years were not significant. ZDVs were consistently highest near the Mississippi River delta and along the western Louisiana/eastern Texas shelf, and moderately high during summer and fall along the shelf break, with localized pockets of elevated volumes over the eastern Gulf shelf. We suggest that Chloroscombrus chrysurus, D. punctatus, T. lathami, and possibly Oligoplites saurus, Hemicaranx amblyrhynchus and Caranx crysos spawn in frontal areas and/or along other hydrographic features that promote higher productivity. We provide new illustrations and descriptive information for the larvae of H. amblyrhynchus and discuss characters that separate early larvae of several species of Caranx.

Abstract: hydrographic ecotopes indicate that the ichthyoplankton density was highest in the East China Sea Shelf (ECS), moderate in the Kuroshio Current (KUR), and lowest in the mixing zone (MIX). In total, 59 789 individuals of ichthyoplankton assigned to at least 124 families and 547 species were collected. The major ichthyoplankton species, comprising about 60% of the total catch, were distinctive in different seasons and waters. Decapterus spp. (14.01%) and Auxis spp. (6.23%) were abundant in spring; Auxis spp. (6.91%) and Benthosema pterotum (5.80%) in summer; B. pterotum (55.23%), gobiids (4.14%), and Synagrops sp. (3.17%) in autumn; and B. pterotum (15.35%) and Gonostoma gracile (7.48%) in winter. The abundant ichthyoplankton species in the 3 hydrographic ecotopes were B. pterotum (22.98%) and Auxis spp. (5.11%) in ECS; Decapterus spp. (28.60%) and Auxis spp. (7.10%) in MIX; and B. pterotum (5.61%) and Vinciguerria nimbaria (4.43%) in KUR. The dendrogram based on major ichthyoplankton species exhibits 7 species-associated groups.