Palaemon
Prawn / Freshwater Prawn
Introduction
It is a nocturnal, bottom-dwelling omnivore inhabiting freshwater rivers, ponds, and streams (some species are marine). It is economically significant as a food source and ecologically vital as a scavenger.
Size & Structure
Size: Varies by species, generally elongated, ranging from 2.5 cm to over 30 cm (e.g., P. malcolmsonii).
Shape: Spindle-shaped, bilaterally symmetrical body divided into cephalothorax and abdomen.
Colour: Usually pale blue or translucent white, turning orange-red when cooked.
Special external features: Body protected by a hard carapace with a serrated, saw-like rostrum extending forward; possesses 19 pairs of jointed appendages.
General Features
- Coelom
- Coelomate (Haemocoel)
- Body plan
- Tube within a tube body plan (Protostomous)
- Germ layer
- Triploblastic
- Metamerism
- Metamerically segmented (Heteronomous segmentation)
- Body symmetry
- Bilateral symmetry
- Fertilization
- External fertilization
- Digestion type
- Complete (Extracellular digestion)
- Nervous system
- Ganglionated double ventral nerve cord
- Excretory organ
- Antennary glands (Green glands)
- Body temperature
- Poikilothermic
- Circulatory type
- Open type
- Development type
- Indirect development (Larval stage: Zoea)
- Respiratory type
- Branchial respiration (Gills)
- Mode of excretion
- Ammonotelism
- Circulation system
- Open (Haemolymph flows in sinuses)
- Skeleton structure
- Exoskeleton (Chitinous cuticle)
- Level of Organisation
- Organ-system level of organisation
- Regulation of Osmosis
- Osmoregulator (Maintained by Green glands)
Ecology
Acts as a scavenger and omnivore, feeding on algae, decaying matter, and small insects.
Serves as a primary food source for larger aquatic predators like fish and water birds.
Helps in cleaning the water body by consuming organic debris and detritus.
Economic Importance
Food Industry: A major source of protein, widely consumed globally as a delicacy.
Aquaculture: Extensively farmed in "Prawn Culture" industries due to high growth rates.
Economy: High commercial export value contributes significantly to the fisheries economy.