Fish, Tanks and Ponds


Fish, Tanks and Ponds
A comprehensive guide to fish

Fish Eyes

 Fish eye anatomy
Fish eye anatomy
 

Introduction

Vision is a major sense for the majority of fishes and so most fishes have well developed eyes and have good vision although it is different to that of most mammals having evolved in a different environment.

Anatomy of a Fishes Eye

  • Aqueous Humour: is a transparent, gelatinous fluid similar to plasma, but containing low-protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens. It is located in the anterior and posterior chambers of the eye, the space between the lens and the cornea. It is not to be confused with vitreous humour, which is contained within the larger cavity of the eye behind the lens.
  • Choroid: The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera.
  • Cornea
  • Falciform Process: The iris of the fish's eye is normally immovable in Teleost's, and very slowly ... layer is enlarged and filled with blood vessels, this is called the 'Falciform Process
  • Iris: In mammals the iris opens and closes to let the right amount of light enter the eye. The iris of the fish's eye is normally immovable in Teleost's, and very slowly moveable in Elasmobranchs, (sharks and rays) taking up to an hour to fully open from fully closed.
  • Lens: The lens of a fishes eye is spherical and non-adjustable which means the focus is fixed and can't be altered to near or distant objects.
  • Ligament: The suspensory ligaments are connecting tissues composed of thin fibers. They connect the ciliary body to the eye's lens.
  • Muscle: Controls eye movement.
  • Optic Nerve: Fish have large eyes, with short optic nerves that are continually flexed by compensatory eye movements during swimming.
  • Pigment Layer: is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual cells.
  • Retina: A thin transparent laminar structure situated at the back of the eye
    The retina is sandwiched between the vitreous body of the actual eyeball, and the sclera
    The retinas of fishes do not differ fundamentally from those of other vertebrates.
  • Sclera: The sclera is commonly known as the white of the eye. It is the tough, opaque tissue that serves as the eye's protective outer coat.
  • Tapeta Licidum: is a layer of tissue in the eye of many vertebrate animals.[2] It lies immediately behind the retina. It reflects visible light back through the retina, increasing the light available to the photoreceptors. This improves vision in low-light conditions

Eye Adaptions

 Omega iris of a fish
The omega iris found in the Loricariidae family of fishes
 

The omega iris can be raised or lowered in order to either To increase or decrease the amount of light entering the fishes eye.

Anableps or Four eyed fish
Anableps or four eyed fish

Anableps or four eyed fish live on the surface and their eyes have evolved to let them see both above and below the water at the same time. Their pupils have almost split and the top half is kept above the water line and the bottom half is kept below the water line. This allows the fish to see prey or danger from above or below.

Although called the four eyed fish and appearing to have two pupils Anableps do in fact only have two eyes.

The migrating eye of larval flatfish

eye migration in flatfishes

Flatfish begin life as ordinary looking symetrical fishes but has they develop one eye migrates to the other side of their head which allows them to use both eyes while lying flat on the ocean floor. Fossils show that this change from a symetrical fish occurred through gradual evolution rather than a sudden leap. The reason for the change is still unknown.

Glossary

 

References

Wikipedia - Tapeta Lucidum
Wikipedia - Pigment layer
Earthlife - Fish sight
stlukeseye - Sclera
Wikipedia - choroid
Wikipedia - Aqueous humour
Fish Tanks and Ponds - Omega iris
PubMed - The design of the optic nerve in fish.
SFDS - Suspensory ligaments
ru.ac.za - Vision