See the world through the eyes of a tadpole

Today we share with you the steps that we take to ensure the healthy development of Common Midwife Toads (Alytes obstetricans) in the breeding centre.

It all starts when adults mate in the outdoor installation of the captive breeding centre in spring and summer, or in the terrarium at the National Park visitor centre year-round. Unlike most amphibians, Common Midwife Toads reproduce on land, and after the male fertilizes the eggs, he carries the clutch for several weeks rolled on his hind legs.

The males will release the eggs into the water. Hatchling larvae are very small so we wait a few days before handling them. After reaching a certain size, we transfer the larvae from the pond or acuaterraterrio into the breeding centre, where we have specially prepared aquariums. In these aquariums we can control temperature and water quality, in addition to observing the animals at all times. UV lamps are necessary to mimic sunlight for calcium metabolism.

Food is a key factor for larval development. Metamorphosed animals are predators of insects and invertebrates, but the tadpoles are detritivores. Periphyton, i.e. algae and other microorganisms which are attached to the walls of water bodies, are also eaten by the larvae. In the breeding centre we supply a diet as varied as possible to replace the rich source of food that the larvae find in nature. We developed a mixture with foodstuffs for fish, trout and rabbits, combining it with spirulina, tubifex worms, small crustaceans and added calcium.

Tadpoles develop their hind legs first and at this time we transfer them to the “beach” aquariums. These are aquariums that contain a zone of gravel where the animals can crawl from the water to complete their metamorphosis. Later the front legs develop rapidly, the tail is absorbed until it disappears, and finally, they complete the development of the mouth.

When newly metamorphosed individuals emerge from the water they are ready to start hunting insects, and are housed with other juveniles in the adult ward.

The larval stage is not only an interim period for our program of conservation breeding and reintroduction. With this project we propose, for the first time, to release larvae and already metamorphosed specimens into the wild. We do not know what stage of development is the most suitable for reintroduction in the case of the Common Midwife Toad, but for other species, the reintroduction of larvae is usually the best strategy. One of the most important advantages of releasing larvae is the development of philopatry in the reintroduced individuals, that is, the tendency to return to the place where they originally completed metamorphosis to reproduce.

In this video you can watch toad larvae in the breeding centre aquariums:

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