Caribbean National Forest

Freshwater Shrimp

If you look carefully into the streams and pools of El Yunque you might see something scurrying across the bottom. It's probably one of the 9 species of shrimp that live in the waters of the forest. Most fresh and brackish water systems of Puerto Rico are inhabited by shrimp of the Atyidae and Palaemonidae family.

Though much is known about salt water species, riverine shrimp are little known. These curious animals have numerous fascinating characteristics and play an important role in aquatic ecosystems as part of the food chain and as recyclers of organic material.

Shrimp, along with crabs and lobsters, are crustacean from the order Decapoda (deca ten. poda foot). The order's name describes one of the features that unite these animals—that they have 5 pairs of articulated legs. Other common characteristics among crustaceans include their aquatic habits, their 14 body segments, and their 2 long antennae.

Shrimp are adapted for swimming. Their bodies are laterally compressed. Their swimmerets are large and fringed and their carapace is thin and relatively flexible. They swim relatively slowly but can dart backwards quickly by flexing their abdomen with their tail fan.

Shrimp are nocturnal animals but can be found during the day in the forest's various pools and rapids. At night they tend to congregate on submerged rocks, tree branches, roots and leaves.

Species and Feeding Habits
In Puerto Rico there are 8 species of shrimp in the Atyidae family, of which 5 are found in El Yunque. The members of this family are filter feeders. They take tiny particles from the water through specialized structures that resemble paint brushes. These structures are found on the first 2 pair of legs (pereiopods). They feed mainly on microscopic diatamous algae and decomposing material. In this manner they aid in the recycling of organic material and also cooperate with the "cleaning'' of the bodies of water.

The other shrimp family found in El Yunque is Palaemonidae. Of the 6 species that inhabit the island, only 4 live in the forest. The members of this family arc predators—they search for, or hunt, their food. They eat insects, small fish, and even other shrimp.

The life stages and reproduction of shrimp are very interesting. Reproduction tends to occur during the summer months, although there are some species that reproduce year-round.

Mating occurs with the male at a right angle to the female, transferring a spermatophore to a specialized receptacle on the female's abdomen. Six to twenty hours after mating the female will carry a large quantity of eggs under her abdomen. The quantity of eggs depends on the species and the individual.

Though they are very active swimmers, these larvae are moved down river towards the estuaries (river mouths) and the sea where they spend their first few days. Those larvae that do not make it to saline water within 4 or 5 days die. The larvae go through a series of transformations in this saline environment for a period of 30 to 50 days. After this time, they become postlarvae or tiny shrimp of approximately 1/2 inch in length. During this period they live and forage near the bottom. They will become reproductively mature within 6 months of reaching their juvenile stage.

These tiny replicas of the adult shrimp then start an upstream migration in search of a pond where they can spend the rest of their life.

This is one good reason why it is so important to maintain clean river waters running to and from the estuaries, for there are many organisms whose life cycles depend on it—including ourselves. Erroneous fishing practices, especially poisoning, overfishing and pollution all contribute to the significant reduction of the shrimp population, as well as other aquatic species.

Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication


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