Common names: Convict Fish, more...
Synonyms: Sparus probatocephalus (Walbaum, 1792)
Species Description: Archosargus probatocephalus is a deep-bodied, compressed fish that reaches 91 cm (35.8 inches) in length, and 9.6 kg (21.2 pounds) or more in weight. The back is elevated behind the head, which is deep and sloping in profile. The snout is short with the mouth inferior and nearly horizontal. The anterior teeth are incisor-like, with posterior molars set further back. There are 6-7 gill rakers on lower limb of the first gill arch. Scales are finely serrate. There is a single dorsal fin, the spinous portion of which is more elongate than the soft portion. There are 12 strong dorsal spines and 10-12 soft rays. The anal fin bears 3 spines, the second of which is the most enlarged, and 10-11 soft rays. The caudal fin is forked.
There are 44-49 lateral line scales. Body color is generally gray or green-yellow base color, marked with 5-7 vertical black bars. The dorsal, anal and ventral fins are typically black or gray to dusky, while the caudal and pectoral fins are more greenish in tone. Coloration is more distinct in young fishes (Hildebrand and Schroeder 1927; Hoese and Moore 1977; Johnson 1978). Juvenile sheepshead are brownish in color and have a median line along the ventral surface. In addition to the vertical black bars, there are also 3 black spots: one set behind the isthmus, one beneath the pectoral fin base, and one set anteriorally to the anal fin (Hildebrand and Cable 1938).
Regional Occurrence: Archosargus probatocephalus is common on the Atlantic and Gulf coasts of the United States. Its range extends from Cape Cod, Massachusetts south through Florida and the Gulf of Mexico to Brazil. Wanderers are occasionally observed as far north as Nova Scotia. It is absent from Bermuda, the West Indies and the Bahamas (Jennings 1985).
IRL Distribution: Sheepshead are common throughout the IRL.
Age, Size, Lifespan: Archosargus probatocephalus grow to approximately 91 cm (35.8 inches) total length (TL) and 9.6 kg (21.2 pounds), though Hildebrand and Schroeder (1927) reported the largest sheepshead recorded weighed 66 kg (145.5 pounds). In most areas, however, sheepshead never achieve this large a size. Maximum lifespan has been estimated at 20 years in Louisiana (Beckman et al. 1991); however most estimates from other regions are lower, ranging from 8 years in North Carolina (Schwartz 1990) to 14 years in Georgia (Music and Pafford 1984). In a Florida study of sheepshead collected from inshore waters, the maximum age for males was estimated to be 13 years, while in females, maximum age was 16 years (MacDonald unpubl. in Murphy 2000).
Abundance: Sheepshead are considered common to abundant throughout the southeastern Atlantic states as well as on the Gulf coast (Jennings 1985).
Reproduction: Archosargus probatocephalus females in Florida and Georgia mature at approximately age 2 (Tucker 1987). However, they apparently mature at somewhat younger ages in Louisiana, where essentially all males older than age 2, and females over 1 year of age were found to be mature (Render and Wilson 1992).
Spawning occurs in late winter and early spring in the coastal mid-Atlantic, south Atlantic and Gulf of Mexico (Springer and Woodburn 1960; Christmas and Waller 1973; Jennings 1985). Off Louisiana, Render and Wilson (1992) reported spawning occurred from late February through late April. In Georgia, spawning occurs primarily in April (Music and Pafford 1992).
Though some evidence has been put forward that suggests spawning may occur in estuaries (Render and Wilson 1992), it is generally believed that sheepshead spawn in the nearshore and offshore waters of the continental shelf. Evidence from Music and Pafford (1984) and Render and Wilson (1992) show that females with hydrated oocytes and post-ovulatory females are more commonly collected from nearshore waters than from estuaries during the spawning season.
Sheepshead appear to be fractional spawners (Render and Wilson 1992). Estimates of spawning frequency are varied, and range from once per day to once every 20 days. (Murphy 2000). Batch fecundity of females is also widely ranging. Females caught in inshore waters had batch fecundities of 1,100 - 40,000 eggs, while females captured offshore had 14,000 - 250,000 eggs.
Embryology: Eggs are buoyant and measure approximately 0.8 mm (0.03 inches) in diameter. They hatch after 40 hours in water temperatures of approximately 25°C (77 °F). Larvae are pelagic and measure 2 - 4.5 mm (0.08 - 0.2 inches) in length (Johnson 1978). Pigmentation in yolk-sac larvae is restricted to one melanophore set at the angle of the jaw, and 3 melanophores set ventrally posterior to the vent. Most melanophores disappear by the time larvae reach 6 mm (0.24 inches) in length (Mook 1977). Larvae persist for approximately 30-40 days, when metamorphosis to the juvenile stage occurs, typically at lengths of approximately 8mm (0.3 inches) standard length (SL) (Tucker and Alshuth 1996).
A study by Parsons and Peters (1989) reported growth rates in both larvae and juveniles of Tampa Bay, Florida as approximately 0.20 mm (0.008 inches) per day. However, a study by Springer and Woodburn (1960) suggests a somewhat faster growth rate of 0.35 mm (0.014 inches) per day, as estimated from average total lengths for young-of-the-year sheepshead in Tampa Bay during June - August.
Though few studies exist that show growth rates in older juveniles and adults, Beckman et al. (1991) reported that between age 1 and 2, sheepshead reach approximately 26 cm (10.2 inches); between age 2 and 3 they reach fork lengths of approximately 30.5 cm (12 inches), and between age 3 and 4 they reach 35 cm (13.8 inches). In Florida, there is an apparent difference in growth rates between east coast sheepshead and west coast sheepshead, with mean growth rate for Atlantic coast fishes slightly larger at age (through age 5) than Gulf coast fishes (MacDonald unpubl. in Murphy 2000).
Temperature: Archosargus probatocephalus have been collected from waters ranging in temperature from 5 - 35.1°C (41 - 95.2 °F)(Perret 1971; Johnson 1978). Tampa Bay juveniles have been collected at temperatures ranging from 12.8 - 32.5 8°C (55.0 - 90.5 °F) (Springer and Woodburn 1960).
Salinity: Sheepshead are a euryhaline species and have been collected from waters in where salinity ranged from 0 - 35 parts per thousand (ppt) (Springer and Woodburn 1960; Kelly 1965; Perret 1971; Perret and Caillouet 1974).
Parasites: Parasites of sheepshead include ciliates, nematodes, trematodes, and isopods; though infestations with these organisms pose no apparent threat to large populations (Norris and Overstreet 1975; Overstreet and Howse 1977; Overstreet 1978).
Trophic Mode: Sheepshead are omnivores. The larval diet consists primarily of copepods, amphipods and other zooplankton (Benson 1982). Juveniles under 50 mm (2 inches) in length primarily consume ostracods, gammarids, mysids, copepods and polychaete worms, and bryozoans (Hildebrand and Cable 1938; Springer and Woodburn 1960; Sedberry 1987), but will take any soft-bodied organisms found in seagrasses.
After reaching 50 mm (2 inches) in length, there is a dietary shift towards hard-shelled organisms such as bivalve mollusks, brachyurans, echinoderms, and barnacles, though small fishes are opportunistically consumed as well (Odum et al. 1982; Jennings 1985; Sedberry 1978). Adults feed primarily on algae and invertebrates. Ogburn (1984) reported that in North Carolina, sheepshead consumed twice as much algae as invertebrate species. However, Sedberry (1987) reported that for adults of the South Atlantic Bight, bivalves, ascidians and echinoderms were important components of the diet in sheepshead larger than 350 mm (13.8 inches) standard length (SL).
In Georgia, Music and Pafford (1984) reported that sheepshead fed primarily on bryozoans, oysters, decapod shrimp, and barnacles.
Habitats: Smaller pelagic larvae are generally collected in surface waters over sandy bottoms, within estuaries, around seawalls or jetties (Spring and Woodburn 1960; Parsons and Peters 1989), nearshore waters, estuaries and bays (Jennings 1985; Parsons and Peters 1989). Juveniles are most common in seagrasses or over muddy bottoms (Odum and Heald 1972; Jennings 1985). Upon reaching approximately 40 mm (1.6 inches) in length by late summer, juveniles begin leaving nursery areas and congregate with adults around stone jetties, piers, wrecks, and breakwaters (Jennings 1985).
Adults favor habitats with some amount of topographic relief, and can be common over oyster reefs, piers, breakwaters muddy shallows, wrecks, and in the Gulf of Mexico, oil platforms (Johnson 1978; Jennings 1985).
Sheepshead are not truly migratory, but do move to offshore spawning grounds with the onset of cooler water temperatures in late fall and winter (Gilhen et al. 1976; Jennings 1985), and return to nearshore waters and estuaries after spawning takes place in spring. Music and Pafford (1984) found that tagged sheepshead in Georgia never moved more than 100 km (62.5 miles) from their tagging sites, with emigrating fishes leaving estuaries for nearshore reefs close to the sites where they were initially tagged.
Associated Species: Sheepshead are commonly landed with white mullet, black mullet, jacks, and mojarras (Murphy 2000).
Special Status: Commercial and recreational fisheries.
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Tucker, J.W., Jr. and S.R. Alshuth. 1997. Development of laboratory-reared sheepshead, Archosargus probatocephalus (Pisces: Sparidae). Fish. Bull., U.S. 95:399-401.