What do fish lice look? - briefly
Fish lice are small, flattened crustaceans measuring roughly 5–10 mm, with a broad, oval body covered by a hard exoskeleton and numerous short bristly setae. They possess eight legs, the front pair transformed into robust claws for attachment, and a pair of antennae ending in sensory hairs.
What do fish lice look? - in detail
Fish lice, commonly referred to as Argulus, are obligate ectoparasites of freshwater and marine fishes. Adults measure 2–6 mm in length, with some marine species reaching up to 10 mm. The body is laterally compressed and covered by a hardened dorsal shield (carapace) that arches over the posterior abdomen. The shield exhibits a smooth to slightly ridged surface, often bearing a pale to brownish coloration, sometimes speckled with darker spots that provide camouflage on host skin.
The cephalothorax bears a pair of prominent, bulbous compound eyes positioned laterally, each composed of numerous ommatidia for detecting host movement. Adjacent to the eyes are short, segmented antennae equipped with sensory setae that locate chemical cues from potential hosts. A robust, ventrally directed maxilliped forms a claw‑like structure used to grasp the host’s integument and to scrape mucus and epithelial tissue.
Six jointed locomotor legs extend from the thoracic region. Each leg ends in a claw equipped with serrated edges, enabling firm attachment to scales, fins, or gill filaments. The legs are covered with fine setae that increase surface area for adhesion. Posterior to the thorax, the abdomen consists of a series of flexible segments ending in a terminal operculum that protects the reproductive openings.
Reproductive anatomy includes paired genital pores on the ventral surface of the abdomen. Females possess a brood pouch (ovigerous sac) within the carapace, capable of holding 20–40 eggs at a time. Eggs are encapsulated in a thin, transparent chorion and attached to the host’s skin or to submerged substrates.
Larval development proceeds through three stages: a free‑swimming nauplius, a parasitic copepodid, and the adult. The nauplius is microscopic (≈0.2 mm), with three pairs of appendages used for swimming. The copepodid resembles a miniature adult but lacks the fully developed dorsal shield and reproductive structures; it actively seeks a host within hours after hatching.
Coloration varies among species: Argulus foliaceus typically displays a brownish‑gray hue with darker dorsal markings, while Argulus japonicus exhibits a lighter, almost translucent body. In all cases, the exoskeleton’s glossy finish reduces friction during host attachment and facilitates rapid movement across the host’s surface.
Overall, fish lice present a compact, armored morphology optimized for clinging to and feeding from fish hosts, with distinct sensory, locomotor, and reproductive adaptations visible across all life stages.