What Ameca Splendens Is and Where It Comes From

Ameca splendens, commonly called the butterfly splitfin or Ameca splitfin, is a small livebearing fish native to a single spring system near Ameca, Jalisco, Mexico. The species is extinct in the wild—its native habitat was destroyed by urban development and water extraction—but it survives in the aquarium hobby and in a few dedicated breeding programs. All butterfly splitfins in captivity today descend from fish collected before the species vanished from nature.

The fish is named for the males' enlarged, sail-like dorsal fins, which they display during courtship and territorial disputes. Males reach about 2 inches long; females grow slightly larger and lack the dramatic fin extensions. Both sexes carry a distinctive black stripe running the length of the body, and the fins often show yellow or orange coloration. The species is ovoviviparous—females give birth to live young rather than laying eggs—which makes breeding straightforward for home aquarists willing to provide the right conditions.

Key Takeaways

  • Ameca splendens requires a tank of at least 20 gallons with stable water temperature between 72 and 82 degrees Fahrenheit and neutral to slightly alkaline pH.
  • Males are aggressive toward each other and will harass females constantly, so keep only one male per tank or maintain a large group with multiple females to spread aggression.
  • The species is extinct in the wild and survives only through aquarium populations, making responsible breeding and record-keeping important for hobbyists who keep them.
  • Females produce 20 to 60 fry every four to six weeks once mature, and fry are large enough to eat small live foods immediately after birth.
  • Ameca splendens is hardy and tolerant of a range of water conditions, but prefers planted tanks with good filtration and regular water changes.

Tank Setup and Water Conditions

A single male and several females need a minimum of 20 gallons, though 30 gallons or larger is better if you plan to keep multiple males or raise fry. The tank should have moderate to strong filtration—butterfly splitfins produce considerable waste—and a heater to maintain temperature between 72 and 82 degrees Fahrenheit. They tolerate cooler water briefly but thrive in the warmer range and breed most readily at 76 to 80 degrees.

Water pH should be neutral to slightly alkaline (6.8 to 7.5), and hardness can range from soft to moderately hard. Weekly water changes of 25 to 30 percent keep nitrate levels low and maintain water quality. The species appreciates live plants—Java fern, Ludwigia, and stem plants work well—which provide cover for fry and help absorb excess nutrients. Avoid sharp decorations; the fish's delicate fins tear easily on rough surfaces.

Lighting should follow a natural day-night cycle of 10 to 12 hours on, 12 to 14 hours off. Ameca splendens is active during daylight and rests at night, and consistent photoperiod supports normal behavior and breeding cycles.

Feeding and Diet

Butterfly splitfins are omnivorous and will eat most aquarium foods. High-quality flake food, small pellets, and frozen foods like bloodworms, daphnia, and brine shrimp form the foundation of their diet. They also graze on algae and plant matter, so a planted tank provides supplemental nutrition. Feed small amounts twice daily, only what the fish can consume in two to three minutes.

Variety matters for long-term health and color. Rotating between flake, frozen, and occasional live foods (such as small live daphnia or mosquito larvae) keeps the fish's immune system strong and brings out the best coloration in males. Females preparing to give birth benefit from extra protein in the form of frozen bloodworms or small live foods.

Male Aggression and Social Structure

Male butterfly splitfins are highly territorial and will fight aggressively with other males, often resulting in torn fins or injury. A single male per tank is the safest approach for most aquarists. If you want to keep multiple males, you need a large tank—at least 75 gallons—with plenty of visual barriers (plants, driftwood, rock formations) so each male can establish and defend a separate territory.

Males also harass females relentlessly, pursuing them constantly and nipping at their fins. In a small tank with one male and one or two females, the female may become stressed and refuse to eat. Keeping at least three to four females per male distributes the harassment and gives females places to hide and rest. A heavily planted tank with multiple hiding spots reduces stress on females regardless of the sex ratio.

Breeding and Fry Care

Ameca splendens breeds readily in home aquariums without special conditioning. Females mature at about four months old and produce fry every four to six weeks once they reach breeding age. A single female can bear 20 to 60 fry per brood, depending on her size and condition. Gestation lasts about 28 to 35 days, and you can often see the developing fry inside the female's body as dark spots near her tail.

Fry are born fully formed and large enough to eat small live foods immediately—newly hatched brine shrimp, micro worms, or finely crushed flake food work well. If fry are born in the main tank with adults present, most will be eaten within hours. To preserve fry, move the pregnant female to a separate breeding tank (10 gallons is adequate) a few days before she is due to give birth. After she releases the fry, return her to the main tank and raise the young separately.

Fry grow quickly and reach 1 inch within six to eight weeks. At that size, they can be moved to the main tank or sold to other aquarists. Keeping detailed records of breeding dates, brood sizes, and which fish produced which offspring helps maintain genetic diversity and prevents inbreeding—especially important for a species that exists only in captivity.

Compatibility with Other Fish

Ameca splendens coexists peacefully with most community fish of similar size or larger. Tetras, rasboras, corydoras catfish, and peaceful plecos make good tank mates. Avoid very small fish (under 1 inch) and delicate species with long, flowing fins—butterfly splitfins will nip at them. Do not house them with aggressive cichlids or other fin-nippers.

Other livebearing fish such as guppies, platies, and mollies can share a tank with Ameca splendens, though they may hybridize if given the opportunity. If you are breeding butterfly splitfins for conservation or record-keeping purposes, keep them in a species-only tank to maintain genetic purity.

Conservation and Hobbyist Responsibility

The butterfly splitfin's extinction in the wild makes every captive population valuable. Aquarists who keep this species should consider themselves stewards of a living archive. Maintaining accurate records of your fish—noting which individuals bred, when, and what the offspring looked like—contributes to the collective knowledge of the species and helps prevent genetic bottlenecks.

Several organizations, including the Association of Zoos and Aquariums and specialty aquarium clubs, maintain studbooks and coordinate breeding efforts to preserve genetic diversity. If you breed Ameca splendens, connecting with these groups or local aquarium societies allows you to share fry with other hobbyists and learn from experienced keepers. Responsible breeding and record-keeping are not optional extras—they are essential to the species' survival.

Frequently Asked Questions

Can I keep Ameca splendens in an unheated tank?

Not reliably. The species comes from a warm spring and does best at 76 to 80 degrees. Temperatures below 72 degrees slow their metabolism, reduce feeding, and stop breeding. In cold climates, an aquarium heater is necessary year-round.

How do I tell males and females apart?

Males have a large, sail-like dorsal fin and a pointed anal fin. Females lack the enlarged dorsal fin and have a rounded anal fin. Females are also slightly larger and rounder in the body, especially when carrying fry.

Will my butterfly splitfins eat their own fry?

Yes. Adult Ameca splendens will consume fry if given the chance. To save fry, move the pregnant female to a separate breeding tank before she gives birth, or provide dense plant cover in the main tank where fry can hide. Even with plants, expect to lose most fry in a community tank.

What should I do if I have too many fry?

Contact local aquarium clubs or fish stores to see if they will take fry off your hands. Some stores buy or accept young fish from hobbyists. You can also cull fry humanely if you cannot find homes for them—this is preferable to letting the population explode and crash from overcrowding.

Are butterfly splitfins hard to keep?

No. They are hardy, forgiving of minor water quality fluctuations, and adapt well to captivity. The main challenge is managing male aggression and deciding what to do with fry. Beyond that, they are straightforward fish for beginners and experienced aquarists alike.