protozoea

Protozoea is a larval stage in the development of many crustaceans, especially decapods such as penaeid shrimp and lobsters. It follows the nauplius stage and precedes the zoea stage. Protozoea larvae are typically free-swimming in the plankton and show an elongated body with a defined cephalothorax partly covered by a carapace, stalked eyes, and developing feeding appendages. The abdomen becomes more apparent as growth proceeds, and the early limb and mouthpart structures differentiate across sub-stages, commonly labeled protozoea I–III in many species.

Feeding and growth generally involve small zooplankton and microalgae. In aquaculture and laboratory settings, protozoea are often reared on microdiets or live feeds such as rotifers and small Artemia nauplii, with feeding regimens adjusted as the larva molts. The duration of the protozoea stage varies by species and environmental conditions, typically lasting from several days to a couple of weeks, with successive molts leading toward the next larval stage.

Ecology and importance: Protozoea occupies the pelagic water column during its development and is subject to environmental factors such as temperature, salinity, and water quality, affecting survival and growth. In natural populations and hatcheries alike, this stage is characterized by relatively high mortality risks and a critical role in shaping subsequent recruitment.

Etymology and terminology: The name protozoea derives from Greek elements meaning “first life stage,” reflecting its position early in the larval sequence. In taxonomic and developmental studies, protozoea morphology and timing are used to distinguish stages within the larval progression.