5 Common Causes of Black Eye in Fish

Fish with black eye

Fish demonstrate their emotions through behavior and physical changes.

For example, the constant hiding of a fish indicates stress, while a fish swimming around freely and actively is a sign of good health.

Sometimes, you find your fish completely healthy apart from its eyes that have turned black.

So, what causes a fish’s eyes to turn black?

5 Causes for Black Eyes in Fish

The eyes of fish give a good indication of their health and behavior.

However, a fish’s eyes turning black indicate several issues.

Some of the most common causes of black eyes in fish are given below.

1. Stress

Stress is one of the reasons for a fish’s eyes to turn black.

Some aquarists have experienced their guppies’ eyes turning black due to stress.

They have noticed the eyes of their pregnant guppy turning black due to the stress caused by the constant chasing of the male guppies.

If the black eyes are caused by stress, it’s vital to reduce the stress levels in the tank.

This is done by ensuring that there is no aggressive fish in the tank.

Additionally, providing plenty of hiding places help reduce stress levels.

2. Tricking Predators

Research has found that guppies turn their eyes black to safeguard themselves from predator attacks.

As per a study, guppies turn their eyes black to deter a predator from attacking.

This usually happens when aggressive fish try to hunt the guppies.

A guppy turns its eyes black so that the predatory fish turns its attention to the head part of its body and attacks the topmost part instead of the usual middle part of the guppy’s body.

This allows the guppy to dodge and escape the aggressive predator swiftly.

While this has been true for guppies, the same can’t be said for other fish species because there is no research to back it up, nor have any aquarists experienced this.

3. Display of Aggression and Dominance

Fish usually guard their food and don’t allow other smaller fish to eat it.

Most fish do this by showing aggression toward the weaker fish.

However, this research states that guppies display aggression by turning their eyes black.

Guppies usually have silver eyes. However, they turn their irises from silver to black when they want to fight with other fish.

Researchers have found that guppies in the wild usually turn their eyes black to protect their food from other fish.

This behavior is more prevalent when food is scarce.

During such times, guppies turn their eyes black to show dominance and aggression toward other fish to protect their food.

The researchers tested the aggressive behavior of guppies by replicating the eye coloration in a test environment.

They discovered that guppies turn their eyes black when they are stronger than the opponent fish and can win a fight against them.

4. Injury

Fish with injury

In some cases, black eyes in fish can be caused by injury.

This is usually due to a physical altercation with another fish or an object in the tank.

Unlike humans, fish don’t have eyelids for protection.

Hence, if the fish accidentally bumps into an object in the tank, it can cause its eyes to turn black.

If the black eyes are caused by an injury, it’s vital to treat the wound and ensure that the fish isn’t exposed to further injury.

Also, it’s crucial to ensure that the tank is free from sharp objects and that there are no aggressive fish in the tank.

Providing plenty of hiding places also helps to reduce the risk of injury.

5. Natural Coloration

Some fish species have naturally black eyes. This is usually due to their genetics and isn’t a cause of concern.

For instance, some Moscow guppy breeds have black circles around their eyes rather than the usual silver.

Some aquarists have also found a constant black ring around the eyes of their fry.

There is no need to worry as these fish naturally have more melanophores that cause their eyes to appear blacker.

Is It Normal for Fish to Have Black Eyes?

Black eyes are normal for fish that have naturally black eyes.

Some fish species, such as the black moor goldfish, have naturally black eyes.

There is nothing to worry about if the black eyes are caused by natural coloration because this is normal for some fish species.

However, if the fish develop black eyes due to stress or injury, it’s a cause of concern and should be addressed immediately.

Also, if the black eyes appear suddenly and without any apparent cause, it’s essential to investigate further and determine the underlying cause.

Do Black Eyes Indicate Blindness in Fish?

Black eyes don’t indicate blindness in fish.

Many aquarists have found one black eye and the other normal eye in calico ryukin fish.

Eye color is just a variation and doesn’t impact the visual capabilities of the fish.

Another example is the Shubunkin fish which has a black-colored iris. However, they aren’t inherently blind.

It’s essential to seek veterinary advice to determine blindness in fish if they exhibit other symptoms, such as cloudy eyes or bumping into objects frequently.

Remember This About Black Eyes of Fish…

Fish eyes turn black due to stress or injury. Research has found that guppies turn their eyes black to display aggression or trick predators to protect themselves. Some fish species, like black moor goldfish or shubunkin fish, have naturally black eyes, which is nothing to worry about.

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