Larval Fish and Egg Key - Freshwater

Resources:For full bibliographic references: LarvalfishID Reference Shelf

NOTE: Meristics at the family level may not be indicative of all species within that family, especially species outside of the key’s geographic region or for families that have limited data available. In addition, because some species have different features at different sizes (e.g., coiled gut at 8mm and s-shaped gut at 19mm), the fact sheets will show all possible options and do not differentiate by size.

Hypophthalmichthys molitrix (Silver Carp)

General information
Where found: Lake Michigan, Mississippi River (Upper), Ohio River System, Tennessee River
Native or non-native species: Non-native

Egg (spawning to hatching)

Appearance and features
Egg shape: Round
Egg color: Transparent or semi-transparent, colorless or nearly so
Yolk color: Yellow or gold or amber
Buoyancy: Buoyant or semibuoyant
Eggs deposited singly or in a mass: Deposited singly
Perivitelline space description: Large (greater than 50% of egg radius)
Yolk segmentation: Yolk granular
Cleavage: Meroblastic

Egg meristics
Egg diameter (mm): (3.5-)4.5-5.6(-6.4) mm

Oil globule diagnostics
Oil globule (presence): Absent
Frequency/number: Numerous

Incubation period (days): 1-2
Incubation temperature (degC): 18.0-24.0 degC

Yolk Sac Larvae - YSL (hatching to complete absorption of yolk)

Appearance and features (body)
Body shape: Elongate, not eel-shaped
Gill openings on each side: Single
Intestine/Gut form: Straight / uncoiled (may be curved but not coiled or folded back on itself)
Spiral valve: Absent

Appearance and features (fins and finfold)
Pelvic fins: Absent
Dorsal fins or finfold location: Origin anterior to vent
Adipose fin: Absent
Caudal fin rays (principal): Absent or fin rays present or developing

Appearance and features (head and mouth)
Head size: Small (< 15% TL), medium (15-20% TL) or large (> 20 % TL)
Snout shape: Short, round or squared off and blunt
Adhesive disc or organ on snout: Absent
Chin barbels: Absent or not well developed
Gular plate between lower jaws: Absent
Opercular spine(s): Absent

Appearance and features (yolk sac)
Yolk sac shape: Bulbous (teardrop or club shape)
Position of yolk sac: Anus immediately posterior to yolk sac
Presence of yolk: Present

Oil globule diagnostics
Oil globule (presence): Absent

Total Length (TL) of yolk-sac larvae (mm): 6.1-8.7 mm
Total length of recently hatched larvae (mm): 6.1 mm
Dorsal fin (number): Single

Preanal myomeres: 25-28
Postanal myomeres: 12-14
Total myomeres: 36-39

Morphometry (as % of Total Length TL)
Postanal length: 28-35 %

Pigmentation (general)
Body or yolk sac: Pigmented
Body (general regions with pigment): Fins, anal or tail region pigmented, internal region pigmented, swim bladder or presumptive swim bladder pigmented, yolk sac pigmented
Body pigmentation details:
      Melanophores abudant, upper and lower edge of myomeres, Notochord pigmented, Preanal finfold pigmented

Yolk color: Yellow

Head: Pigmented
Eyes: Pigmented
Head pigmentation details:
      Pigment on dorsum of head, cleithrum pigmented, pigment between eyes

Eye pigmentation details: Yellow

Larvae (complete absorption of yolk to development of full complement of adult fin rays and absorption of finfold)

Appearance and features
Body shape: Elongate, not eel-shaped
Gill openings on each side / gill characteristics: Single
Anus (vent) location: Mid-body or rear (posterior)
Presence of swim bladder: Evident (visible)

Appearance and features (fins)
Adipose fin: Absent, no adipose fin or position not evident in finfold
Caudal fin and peduncle: Homocercal or isocercal tail (both lobes symmetrical) or caudal fin forked or bi-lobed, Present, caudal fin rays visible
Pectoral fins: Present
Median (dorsal and/or caudal) fins: Soft-rayed only, Median fins/finfolds show distinct separation
Dorsal fin rays (presence): Absent or dorsal fin rays and/or spines visible

Appearance and features (head and mouth)
Snout shape: Rounded
Snout length: Snout short (< 10 % of Total Length TL)
Chin barbels: Absent or not well developed
Eyes: Large (greater than 5% Total Length TL) or moderate to small (2-5% Total Length TL), Eyes round
Directional position of mouth: Terminal

Total length (mm): 8.7-34.0 mm
Length at flexion (mm): 9.4 mm
Caudal fin ray count: 9
Number of dorsal fins: Single
Dorsal fin ray and spine count: 9

Preanal myomere count: 25-28
Postanal myomere count: 12-14
Total myomere count: 36-39

Pigmentation (general)
Body: Pigmented, Pigment scattered over body, chromatophores small, upper and lower edge of myomeres pigmented, often in rows dorsolaterally, midlaterally, along ventral margin of myomeres and midventrally
Body (general regions with pigment): Lateral pigmentation present, fins, tail and/or anal region pigmented, internal region pigmented, swim bladder pigmented
Body areas without pigment: Venter unpigmented or fading, No midlateral stripe/band or stripe indistinct, No pigment on midlateral myoseptum
Body pigmentation details:
      Cleithrum pigmented, Concentration of melanophores around urostyle, Some or all fins pigmented, Melanophores on the anal finfolds, Caudal fin pigmented, Chromatophores present in dorsal finfolds, Pectoral fin or fin buds pigmented, Notochord pigmented

Head: Pigmented
Eyes: Pigmented
Head (general regions with pigment): Dorsum of head pigmented
Head pigmentation details:
      Prominent dark spot on the inner ventral aspect of eye