Vertical distribution and the role of physical processes in the feeding dynamics of two larval sciaenids Sciaenops ocellatus and Cynoscion nebulosus

Abstract

Red drum Sciaenops ocellatus and spotted seatrout Cynoscion nebulosus larvae were collected using plankton and benthic-sled tows every 2 h for 26 h on 4 separate dates in late August to early October 1990 in Aransas Bay, Texas, USA. Gut contents and gut fullness were evaluated to determine if feeding was randomly distributed over depth and time, and to compare feeding between the 2 species. Calanoid copepods were the dominant prey over all size-classes of red drum larvae. Copepod nauplii, bivalve and barnacle larvae were important for small red drum, while calanoid copepods, dinoflagellates and soft-bodied organisms were important in the diets of large red drum larvae. Calanoid copepods and bivalve larvae were the most important food items for spotted seatrout; gastropod veligers and copepod nauplii were also important prey. Gape size was positively correlated with standard length in both species. Mean prey size increased with gape width but there was wide variation in prey size at any given gape width. Small (<3.0 mm) and medium (3.0 to 4.5 mm) fish of both species fed on similar prey but large (>4.5 mm) fish had distinct diets. Similar numbers of larvae were collected in surface and bottom waters (6 m) during the night, but during the day more larvae were collected in bottom waters. Larvae of both species fed primarily during daylight hours. Feeding extended 2 h later in the evening for spotted seatrout than for red drum. There was no significant relationship between current speed and gut fullness in spotted seatrout or in red drum. Larvae were very successful at feeding under all conditions with little indication that vertical dstribution was associated with feeding success. Transit periods through well-mixed tidal inlets may provide excellent feeding opportunities, as well as a route to transport larvae to essential nursery habitats.

Buccal apparatus and gastrointestinal tract dimensions associated to the diet of early life stages of Centropomus undecimalis (Centropomidae, Actinopterygii)

“…These authors observed that the maximum size of ingested prey was smaller than the maximum mouth gape size, which suggests that mouth size limits the size of items captured by C. undecimalis juveniles. As such, individuals with larger mouth size are able to ingest larger prey and are therefore not selective for smaller-sized prey (HOLT & HOLT, 2000). This fact explains the presence of small prey also in the diet of larger juveniles, as observed herein.…”

“…Juveniles, in contrast, showed greater amplitude in food item size, indicating that the size of ingested prey increases in larger predators, whereas the minimum size of ingested prey changes little for a wide range of predator sizes (SCHARF et al, 2000). The intake of small prey by different size classes and an increasing variation in prey size with growth has been recorded for other carnivore species (HOLT & HOLT, 2000). According to MAGNHAGEN & HEIBO (2001), predator mouth gape size and prey body height are the main factors that determine whether a piscivore with limited gape size can ingest its prey.…”

Role of an estuarine fisheries reserve in the production and export of ichthyoplankton

“…Ichthyoplankton surveys commenced within 48 h of each new and full moon, times of elevated sciaenid spawning activity in the southeastern USA (Peters & McMichael 1987, McMichael & Peters 1989. Most surveys (44 of 48) were conducted at night because sciaenid larvae (and many other taxa) exhibit a fairly uniform distribution in the water column at this time (Holt & Holt 2000). Eight ichthyoplankton tows were made within most subbasins on each survey with locations chosen using a random point generator in Arcview 3.2 GIS software.…”

Monoculture of the ciliate protozoan Euplotes sp. (Ciliophora; Hypotrichia) fed with different diets

“…Food for fish larvae is usually determined by fish mouth size, prey size and fish ability to prey, which suggests that small prey with slow swimming, such as ciliate and dinoflagellate protozoa would be more suited GALLAGER, 2000, HUNT VON HERBING et al, 2001). In the majority of marine fish larvae, especially the ornamental ones, e.g.…”

“…Because of their abundance and size -similar or even smaller than nauplii of copepods, probably they occupy an important position on aquatic trophic food web. According to Holt and Holt (2000), marine fish larvae in the wild commonly feed on a large array of microzooplankton, including protozoa (tintinnid and ciliates), dinoflagellates, larvae of mollusks and, mainly, eggs and nauplii of copepods. However, there are few studies on their role as source of live food in the early stages of fishes and invertebrates (KRAUL, 2006 apud CÔRTES;TSUZUKI, 2012, OLIVOTTO et al, 2005THOMPSON et al, 1999).…”