The brown shrimp, Penaeus aztecus, is a species of grooved, burrowing shrimp, common in Florida waters. Antennae are significantly longer than body length. Its carapace has a medial carina on the anterior surface that is bordered on either side by a broad, somewhat rounded groove. The prominent rostrum is slightly upturned with 5-10 sharp teeth on the upper edge. The integument is thin and translucent in appearance. Chromatophores give the animal a brown to olive-green appearance, though both red and green specimens of this species have been reported. The first 3 pairs of walking legs are chelate. Uropods are rounded and generally colored reddish-brown in the distal portions. The telson bears a sharp tip and a deep medial groove anteriorally. This species exhibits sexual dimorphism, with females growing larger than males. Generally, males attain only 3/5 of female weight, and 5/6 of female length. Females are further distinguished by the presence of a closed thelycum located on the ventral sternum of the thorax, while males are identified by the presence of the pentasma.

Martha's Vineyard, Mass. Around peninsular Florida to Sanibel grounds; Appalachiocola Bay, Fla., around Gulf of Mexico to northern Yucatan.

Gulf of Mexico, North West Atlantic

Brown shrimp occur along the Western Atlantic coast from approximately Martha's Vineyard, MA through Florida and the Gulf of Mexico to the lower Yucatan Peninsula (Williams 1984). P. aztecus occurs throughout the Indian River Lagoon.

Large specimens of P. aztecus males attain an adult size of approximatley195 mm in length, while large female specimens may reach 236 mm in length (Williams 1955). Growth rates for juvenile P. aztecus in North Carolina were estimated by Williams (1955) to be 46 mm per month. In Louisiana, Wilson (1969) estimated growth rates ranging from 45 - 50 mm per month, with overall growth decreasing with age.Growth slows markedly when brown shrimp reach approximately 100 mm. Beyond this size class, male growth slows in comparison to female growth.

P. brasiliensis

Depth range based on 962 specimens in 1 taxon.
Water temperature and chemistry ranges based on 215 samples.

Environmental ranges
  Depth range (m): 0 - 137.16
  Temperature range (°C): 17.205 - 25.874
  Nitrate (umol/L): 0.289 - 4.437
  Salinity (PPS): 33.112 - 36.373
  Oxygen (ml/l): 4.119 - 5.619
  Phosphate (umol/l): 0.100 - 0.424
  Silicate (umol/l): 0.756 - 3.373

Graphical representation

Depth range (m): 0 - 137.16

Temperature range (°C): 17.205 - 25.874

Nitrate (umol/L): 0.289 - 4.437

Salinity (PPS): 33.112 - 36.373

Oxygen (ml/l): 4.119 - 5.619

Phosphate (umol/l): 0.100 - 0.424

Silicate (umol/l): 0.756 - 3.373
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Depth range based on 3 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 174 - 174
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

P. aztecus, like other penaeids, is an opportunistic omnivore that consumes some algal species (i.e., filamentous green algae, benthic diatoms, plant detritus, etc.) as well as small invertebrates such as copepods, mollusks, and annelids (Dall 1968; Odum and Heald 1972).Jones (1973), in a Louisiana study, found a dietary shift in P. aztecus as body size increased. Small shrimp measuring 22 - 44 mm in length were observed to feed nonselectively on top-layer sediments. Shrimp in a larger size class, from 45 - 64 mm in length, became selective in their feeding, preferring only organic materials from top-layer sediments. Larger shrimp, from 65 - 100 mm in length became predatory, feeding on annelid worms, amphipods, zooplankton larvae, and nematodes.Competitors: P. aztecus is likely to compete with other crustacean species, as well as with some fishes for access to invertebrate prey.Habitats: Brown shrimp are commonly found in estuaries and littoral zones along coasts. Primary habitats for these shrimp are muddy bottom areas from the intertidal zone to approximately 110 m. The greatest density of P. aztecus occurs at depths between 27 - 55 m. This species is rarely observed at depths exceeding 165 m (Williams 1984).In laboratory studies of substrate preference (Williams 1958), P. aztecus favored sandy mud and loose peat substrates over other offerings such as loose sand, and shell sand.Activity Time: P. aztecus is a burrowing shrimp that is considerably more active at night in open waters than it is during the daylight hours (Williams 1984).

P. aztecus can be abundant throughout its range and commercial catch rates for this species sometimes surpass those of other penaeids. The area around the Bay of Campeche, TX is one area where this species is highly abundant.Locomotion: P. aztecus is an active swimmer and burrower.

P. aztecus becomes reproductive after reaching a size of 140 mm (Renfro 1964). This species is known to have an extended spawning season that is likely to vary in different geographic areas of its range. Gonads mature in August and become opaque white, yellow or tan in color when fully ripe (Broad 1950; Brown and Patlan 1974). Brown shrimp spawn offshore at depths that generally exceed 18 m (Larson et al. 1989)Data from Burkenroad (1939) showed that sex ratios of P. aztecus change with water depth. In Louisiana waters, the sex ratio nearshore is balanced at approximately 1:1. However, in deeper waters ranging from 90 - 130 m in depth, the sex ratio changes to 1:2 in favor of females. Impregnated females in these waters occurred only beyond 18 m depth. This occurrence pattern is suggestive that spawning sites for P. aztecus are likely to be further offshore in deeper waters than occurs in other Penaeids such as P. dourarum (pink shrimp) and P. setiferus (white shrimp).

Eggs of P. aztecus are demersal and spherical, measuring approximately 0.26 - 0.28 mm in diameter (Pearson 1939 IN: Larson et al. 1989). Hatching occurs with 24 hours. Larvae develop offshore through 5 naupliar, 3 protozoeal, and 3 mysis stages before metamorphosing into postlarvae (Cook and Murphy 1969, 1971). Several postlarval stages occur prior to metamorphosis to the juvenile stage. Larval development takes approximately 11 days at a temperature of 32? C, and approximately 17 days at a temperature of 24? C (Cook and Murphy 1969).In studies of wild Penaid populations, P. aztecus larvae are most commonly sampled below mid-depth. Protozoea of this species are likely to occur nearest the bottom, while postlarval stages occur at, or slightly above mid-depth. However, all stages ascend to surface waters with the onset of darkness.Postlarvae return to coastlines on surface current during late winter and spring (Bearden 1961). Recruitment studies in the Carolinas revealed that postlarval P. aztecus began entering sounds in North Carolina from October through May, with peak recruitment in March and April (Zamora and Trent 1968). In South Carolina, P. aztecus postlarvae are found in all months of the year, with recruitment peaking during February and March (Bearden 1961). Juveniles are collected beginning in mid-April and continuing throughout the summer months (Williams 1955). In one Texas study, Copeland and Truitt (1966) observed that spring recruitment peaks were greatest during evening flood tides.Young P. aztecus postlarvae enter estuaries on flood tides and migrate to shallow, low-salinity waters. Growth is rapid during the warmer summer months. As they grow, they begin migration into progressively more saline waters, eventually returning to offshore areas.

Commercially importantFisheries Importance: The brown shrimp is a highly valued commercial fishery species both within Florida and nationally. The statewide commercial catch of brown shrimp, Penaeus aztecus, between the years 1987 - 2001 was 31.5 million pounds, with a dollar value of over $71.1 million. Within the 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties) the commercial catch of brown shrimp accounts for approximately 16% of the statewide total, with a harvest of 4.6 million pounds, and a value of over $11.6 million.This ranks the brown shrimp tenth in commercial value within the IRL, and sixteenth in pounds harvested.Figure 1 and Table 1 below show the dollar value of the brown shrimp fishery to IRL counties by year. As shown, commercial catch ranged from a low of $65,978 in 1988 to a high of over $1.9 million in 1996. Brevard County accounted for the bulk of the commercial catch in most years, with 58% of the total brown shrimp harvest in the IRL area. Volusia County ranked second, with 32% of the harvest.St. Lucie County reported commercial harvests for brown shrimp in only 5 years, from 1993 - 1998, yet accounted for 10% of the total catch. Commercial catches for brown shrimp were not reported from either Indian River or Martin Counties.Benefit in IRL: Brown shrimp are commercially important in Florida. Fisheries data from 1996 shows brown shrimp catches in Brevard County, Indian River County and Martin County of approximately 906,900 pounds of the state-wide catch (data provided by Florida Department of Environmental Protection). Two other counties, St. Lucie and Volusia did not report commercial harvests of brown shrimp. In these counties, rock shrimp made up the bulk of commercial harvesting efforts.Statistics from the National Marine Fisheries Service show that state-wide in Florida during 1998, 250 metric tons of brown shrimp were harvested, with a value of $1,475,059. In 1999, state-wide captures of brown shrimp were 395 metric tons, at a value of $2,163,466.