- Why don't we start out with a basic shrimp life history
All penaeid shrimps have much the same life cycle. Spawning usually occurs in the ocean from near the beaches to several miles offshore. A single female produces between 500,000 and 1,000,000 eggs and may spawn several times.
During mating, the male transfers a packet of sperm, called a spermatophore, to the female. Brown and pink shrimps mate when the female’s exoskeleton is still soft immediately after molting. The spermatophore is covered over by two “plates” that hold it in place. Spawning in the species may take place days later. Mating of white shrimp occurs between two “intermolt” (hard exoskeleton) individuals. The spermatophore is glued to the underside of the females and spawning occurs almost immediately. Eggs, which are fertilized as they are ejected past the spermatophore, are thought to sink to the ocean floor and after about 12 to 24 hours hatch into minute larvae that move into the water column.
The initial larval stage, which looks like a tiny mite, is followed by about 10 larval phases, reaching the post-larval stage after about two weeks. Postlarvae look like miniature versions of adult shrimp. White and pink postlarvae are about 1/4 inch and brown postlarvae are about 1/2 inch in length when they enter the coastal inlets. The transport mechanisms that carry postlarvae into the estuaries are not fully understood, but it seems that the postlarvae will become active and move up into the water column during flood tide and settle to the bottom during ebb tide. Thus, this behavior moves postlarvae farther inshore every tidal cycle until they settle out in the nutrient-rich tidal creeks and marshes.
Natural mortality rates are extremely high for larval and juvenile shrimp. Probably less than one or two percent of the eggs spawned will survive to be adult shrimp.
Post larval shrimp seem to settle out in the shallow waters in the upper ends of saltmarsh tidal creeks. Shrimp will remain in this “nursery habitat” about two or three months until they are about four inches in length. During high tide, juveniles move into the marsh grass to feed and escape predators. At low tide, when the water level is below the saltmarsh grass, shrimp concentrate in creek beds. The smallest shrimp remain near the creek bank while larger juveniles tend to be in deeper creek waters. If the water is unusually clear, shrimp will seek the deepest areas available, presumably to avoid predatory birds, fish and crabs. In other regions of the Southeast where tides are very small or nonexistent, juvenile white shrimp are known to remain in the saltmarsh grass until they are ready to move seaward. (eg. Mosquito Lagoon)
Both brown and white shrimp seem to prefer muddy bottom but pink shrimp appear to do best on a sand/shell bottom.
Growth is very rapid while in the nursery habitat, up to 2 to 2 1/2 inches per month. Shrimp, like all other arthropods, must molt (shed the old exoskeleton) in order to grow. Small shrimp may molt several times per week, but as they become larger, time between molts becomes greater. Ideal nursery habitat has brackish water that is about 25 to 40 percent sea water for white shrimp and 35 to 65 percent sea water for brown shrimp. Shrimp have been known to do well, however, in water that was near 100 percent sea water or in 10 percent sea water.
Of the shrimp that reach an adult size, most die before they’re eight or nine months old. The size record for white shrimp (just over ten inches) was caught by a commercial shrimper off Seabrook Island SC in July 1979. This individual had probably been spawned in May the previous year making it 14 months old. It’s doubtful that any shrimp live longer than two years.
Stomach contents of shrimp are difficult to identify because the food is torn and shredded by the mouth parts. Shrimp are generally termed bottom-feeding omnivores, meaning that they will eat most organic materials - animal or plant - that they encounter at the bottom. One study suggested that small shrimp, less than about two inches in length, indiscriminately ingest the top sediment layer. Shrimp 2 to 2 1/2 inches select the organic portion of the sediment and larger shrimp become more active predators, feeding on small animals. Animals commonly listed as food are polychaete worms, amphipods, nematodes, crustacean larvae, isopods, copepods, small fishes, grass shrimp, fiddler crabs and square-back crabs. Shrimp are also known to be cannibalistic. One researcher speculated that bacteria are the main living component in the food of shrimp. Shrimp are thought to scavenge dead animals that may be leftovers from other predators. The effectiveness of bait, particularly oily fish, indicates that shrimp are able to home in on odors.
That is all the info I have on life cycle. Feel free to add anything about life cycle that you know (I know some of you might be tempted to add other things, but let's keep this in order, so it is easy to search)
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