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Trout Goodeid: A Comprehensive Guide (Ilyodon furcidens)

The Trout Goodeid, Ilyodon furcidens, is one of those fish that doesn’t look like it belongs in a typical aquarium—and that’s exactly why people love them.

They’ve got that:

  • Streamlined, almost trout-like body
  • Silvery sheen
  • Strong, constant swimming behavior

This is not a slow, planted-tank fish.
This is an active, always-moving, current-loving species that brings a completely different energy to a tank.

And unlike most livebearers people are used to… this one comes with a bit more attitude and personality.

Origin & Habitat

This species comes from Mexico, where it inhabits:

  • Fast-moving rivers and streams
  • Clear, oxygen-rich water
  • Rocky or gravel substrates

Natural conditions include:

  • Cooler temperatures than typical tropical fish
  • Moderate to strong flow
  • High oxygen levels

This is a fish built for movement—not still water.

Size

  • Adult Size: ~4 to 5 inches
  • Body Type: Streamlined, torpedo-shaped

They get bigger than most people expect, and they use that size.

Tank Size

  • Minimum Tank Size: 40 gallons
  • Recommended: 55+ gallons

More important than gallons:

  • Swimming space
  • Flow
  • Group size

These are active schooling fish, not something you keep as a pair.

Water Parameters

  • Temperature: 65–75°F
  • pH: 7.0–8.0
  • Hardness: Moderate to hard

Key factors

  • Cooler water
  • High oxygen
  • Good flow

Running them like a tropical community fish (78–80°F, low flow) is a mistake.

Temperament

  • Semi-aggressive
  • Active
  • Social within their group

Important notes

  • They can nip slower fish
  • They establish hierarchy
  • They’re not shy

Best kept:

  • In groups of 6+

Too few = more aggression
Proper group = more balanced behavior

Tank Setup

Think river tank, not planted display tank.

Ideal setup

  • Strong filtration / flow
  • Open swimming space
  • Rocks and structure
  • Minimal delicate plants

Why this matters

They are:

  • Constant swimmers
  • Oxygen-demanding
  • Not interested in sitting still

A slow, heavily planted tank:

  • Looks nice
  • Doesn’t match their behavior

Diet

Very easy—and they eat a lot.

Staple foods

  • Quality flakes
  • Pellets

Additional foods

  • Vegetables (zucchini, spinach)
  • Frozen foods
  • Algae-based foods

They are:

  • Omnivorous with a strong herbivorous lean
  • Constant grazers

Feed them well or they’ll start sampling plants.

Tank Mates

This is where you need to think carefully.

Best options

  • Similar-sized, active fish
  • Other cooler-water species

Avoid

  • Slow fish
  • Long-finned fish
  • Small, delicate species

They’re not outright aggressive—but they’re:

Too active and too nippy for calm community tanks

Behavior

  • Constant swimmers
  • Mid to upper water column
  • Highly active and interactive

They’ll:

  • Cruise the tank nonstop
  • Interact with each other constantly
  • Establish pecking order

They bring a lot of movement to a tank.

Breeding

Unlike typical livebearers, goodeids are a bit different.

Reproduction

  • Livebearers
  • Produce fewer, larger fry
  • Fry are more developed at birth

They also have:

  • A different reproductive structure than guppies/mollies

Breeding usually happens naturally in stable groups.

Why They’re Rare

A few reasons:

1. Not beginner-friendly

They don’t fit the typical “community fish” mold.

2. Cooler water requirements

Limits where they can be kept.

3. Niche appeal

More of an enthusiast species than a mainstream one.

Final Thoughts

If you want:

  • Something completely different
  • A high-energy, active fish
  • A species that feels more like a river fish than a tropical fish

The Trout Goodeid is a great choice.

But this is not a “set it and forget it” community fish.

It’s a:

“build the tank around the fish” type of species

Looking to Add Fish to Your Aquarium?

If you're looking to add new fish to your aquarium, we recommend purchasing from trusted retailers known for their healthy livestock and excellent selection. The Wet Spot Tropical Fish has one of the best selections of rare and high-quality freshwater fish in the hobby, with excellent shipping and consistently healthy stock. Moonlight Aquatics is another fantastic source, especially for uncommon species and great prices on unique fish you don’t see everywhere. If you’re looking to add shrimp to your tanks, Buy Pet Shrimp specializes in hardy, well-bred freshwater shrimp that ship safely and arrive in great condition.

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