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The Mooneye (Hiodon tergisus) is a freshwater ray-finned fish belonging to the family Hiodontidae, which also includes the Goldeye (Hiodon alosoides). It is characterized by its large, prominent eyes, silvery coloration, and compressed body. Mooneye are active predators, particularly at night, and are known for their leaping behavior when hooked by anglers. They are an important forage fish in many ecosystems.
Physical Characteristics
- Body shape
- compressed
- Coloration
- Silvery on the sides and belly, with a darker, often greenish-blue or olive-brown back. Fins are typically clear or dusky.
- Scale type
- cycloid
- Mouth position
- superior
- Distinctive features
- Very large, prominent eyes, giving it the 'mooneye' name., Deep, compressed body., A keel (sharp ridge) along the belly, extending from the pelvic fins to the anus., Dorsal fin originates behind the origin of the anal fin., No adipose fin.
- Dorsal fin
- Single, short-based dorsal fin with 11-12 soft rays, originating posterior to the anal fin origin.
- Tail fin
- Deeply forked caudal fin.
- Pectoral fin
- Pectoral fins are relatively small.
- Distinctive fins
- Pelvic fins are abdominal (located far back on the belly). Anal fin is long, with 28-31 soft rays.
Identification Tips
Eye Size
The most distinguishing feature is its exceptionally large, prominent eye, which is noticeably larger than that of the similar Goldeye.
Dorsal Fin Position
The dorsal fin originates distinctly behind the origin of the anal fin. In contrast, the Goldeye's dorsal fin originates anterior to or directly above the anal fin origin.
Ventral Keel
Possesses a sharp, bony keel along its belly, extending from the pelvic fins to the anus. This is a shared feature with Goldeye.
Body Shape
Generally deeper-bodied and more compressed than the Goldeye.
Habitat
- Water type
- freshwater
- Depth
- Typically found in shallow to moderately deep waters, often near the surface at night.
- Environment
- Prefers large, clear rivers, lakes, and impoundments with moderate to strong currents. Often associated with open water but may seek cover in submerged vegetation or structure. Tolerant of some turbidity.
- Geographic range
- Native to North America, primarily in the Mississippi River basin, Great Lakes region, and Hudson Bay drainage. Extends from Quebec and Ontario south to Louisiana and west to Montana.
Aquarium Information
- Care level: expert
- Temperament: semi-aggressive
- Diet: carnivore
- Minimum tank size: 500 gallons
- Temperature: 10-22°C (50-72°F)
- pH level: 7.0-8.0
- Hardness: 100-250 ppm
- Compatibility: Not suitable for typical home aquariums due to size, activity level, and specific environmental needs. Best kept in large public aquariums with similar-sized, robust fish.
- Special requirements: Requires very large, well-filtered tanks with strong current and ample swimming space. Sensitive to poor water quality. Live or frozen foods are essential. Not commonly kept in captivity.
Wild Information
- Conservation status: least concern
- Seasonality: Spawns in spring (April-June). Active year-round, but often targeted by anglers in spring and fall.
- Market price: Low
- Commercial importance: low
- Taste: Mild, somewhat oily
- Texture: Flaky, but bony
- Cooking methods: Smoking, Frying, Pickling
- Nutritional value: Good source of protein and omega-3 fatty acids, though not widely consumed due to numerous small bones.
Key Facts
Nocturnal Hunterbehavior
Mooneye are primarily nocturnal predators, using their large eyes to hunt insects, small fish, and crustaceans in low light conditions.
Leaping Fishbehavior
Anglers often report Mooneye leaping out of the water when hooked, a characteristic behavior that makes them an exciting catch.
Ancient Lineageevolution
The family Hiodontidae, to which Mooneye belong, is considered a primitive group of teleost fish, with a fossil record dating back to the Eocene epoch.
Forage Fishbehavior
Mooneye play a crucial role as a forage fish, providing a food source for larger predatory fish like walleye, northern pike, and various birds of prey.
Safety Information
Safe- Safety level: safe
- Venomous: No
- Edibility: edible
- Handling notes: No specific handling precautions are required beyond standard fish handling to avoid fin pricks. They are not venomous and do not possess sharp spines that pose a significant threat. Can be quite slippery.
Similar Species
Goldeye
Hiodon alosoides
The Goldeye has a golden iris (Mooneye has a silvery iris), and its dorsal fin originates anterior to or directly above the anal fin origin. The Mooneye's dorsal fin originates distinctly behind the anal fin origin. Goldeye also tends to be more slender.
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Actinopterygii
- Order
- Hiodontiformes
- Family
- Hiodontidae
- Genus
- Hiodon
- Species
- Hiodon tergisus
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