Three forms of vertebrates are commonly found in Welsh caves – fish, amphibians and bats, although they are either accidental or using them for shelter. It is thought there is not enough food for them to survive as troglobites in UK caves.

Fish

Bullheads (Cottus gobio) are found in caves. It is not known how long an individual will spend in a cave but they can be found year round. They do not seem to be affected by the dark and their colour does not seem to change. There must be a reasonable population in Porth yr Ogof to replenish those squashed by cavers feet. They are a bottom dwelling fish adapted to life in fast, well oxygenated water. Their eyes have a double cornea with fluid in between presumably to protect them from sand particles flowing in the stream. They feed on invertebrates such as mayfly larvae, freshwater shrimps and midge larvae. Eggs are laid March to June and the male guards them for a month.

Bullhead (Cottus gobio) in main stream of Porth yr Ogof.

Blanched brown trout (Salmo trutta) are found in caves – their colour is rapidly restored on exposure to daylight. Unlike some of their foreign counterparts these trout are not blind. They are trogloxenes with no genetic modification. Colour and marking on brown trout is very variable, those inside Ogof y Ci initially look like white/pink oval rocks as they are often motionless until disturbed. They feed mainly on Crustaceans and insect larvae that they can detect in the absence of light - they can even take metal lures of fishermen in the dark.

Blanched Brown Trout (Salmo trutta) in Ogof y Ci. The proportionally large head and slim body may indicate an old male but more probably an undernourished fish.

Other fish may be found especially near the sea e.g. Goby (Pomatoschistus sp) in Otter Hole, Minnow (Phoxinus phoxinus) in Little Neath River Cave, Flounder possibly in Merthyr Mawr Cave. The flounder is the only flatfish regularly found in freshwater. You may also find eels (Milwr Tunnel), salmon or stickleback.

Ogof Draenen has examples of fossilised fish.

Amphibians

Common Frogs (Ranus temporaria) can be underground, but presumably are accidental visitors and often look thin. They can be found a long way underground, presumably lost and will eventually starve. Toads and newts are occasionally seen but are usually close to entrances, most commonly below entrance shafts as they are unable to climb out. Amphibians may enter the cave for shelter, especially in winter, or are accidentally washed in during floods.

Malnourished frog at the end of Dan yr Ogof show cave.

Toad by the Letterbox, Porth yr Ogof.

Palmate newt, Triturus helveticus, below entrance shaft of Pwll Pindar