Finding myself in Denmark for a period of time, I decided to try and keep some native aquatic species in a home "akvarium". Although I spotted some pretty silver fish with red tails in a lake near Silkeborg, I had no idea how I could net the minnow-sized fish I was after. I decided instead to see what I might find at a small pond on my father-in law's farm. Within a few minutes of looking, I was lucky to scoop up a baby salamander that was scooting along the pond's muddy bottom. Knowing that these fellows are rather rare in Denmark, however, I did not have the heart to keep it and so released it after a moment's study. I couldn't see much else in the pond at the time (early March) and so put my native-species aquarium plans on hold.

Note the external gills present on this baby salamander

My question of what to keep was solved one warm day later in March when my youngest son came bounding in the kitchen, hollering that there were "frogs outside making a big ball in a pond!" Wondering what he was talking about, I went out to investigate and, sure enough, there were around 10-15 frogs bound together in a "ball". As a child I once witnessed common Gardner snakes forming a similar "ball" when mating, and so concluded that these frogs were doing the same thing.

The "frog" pond

Some adult frogs busy reproducing

My father-in law later told me how when mating the female frog or toad is typically stuck in the middle of a group of males, all of whom cling on tightly while trying to impregnate her. It's not uncommon for the action to get so frantic that some of the animals even drown in the process! Yuck! Anyway, on my father-in law's advice, I decided to come back in about 4-6 weeks to see if there were some eggs to collect.

One day in mid April there they were - gelatinous masses of eggs. Each mass measured around 6-12 inches in diameter, leading me to think that the eggs must expand upon being laid by the female.

Masses of frog eggs - the developing embryos are clearly visible

A closer view

Using a bucket we scooped up a few hundred eggs to put in the empty 10 gallon tank we had prepared at home. For filtration, I initially thought of using a small internal power filter covered with a nyon stocking (to prevent any small creatures from getting sucked in). That quickly turned out to be a bad idea, however, as the current generated by the filter's outflow blew the egg mass all over the place. I decided to leave the water undisturbed and to see what would happen. Given the warm room temperature of our house, the eggs developed much faster than those that were still outside in the pond. Unlike raising tropical fish eggs, I did not seem to lose any to fungus.

Frog eggs at home in a 10 gallon aquarium

Within a week of being brought inside the eggs hatched. The newly hatched tadpoles clung to the outside of the jelly egg mass and sucked on it for nourishment. They seemed to double in size daily.

Newly hatched frogs eating their egg jelly

Another view of newly hatched frogs (with sunlight)

Within two weeks the jelly mass was gone and the now free-swimming tadpoles were eager for other foods. Some fish flakes worked well and the tadpoles continued their rapid growth rate. Periodically I removed some tadpoles to release in nearby ponds. My father-in law told me how when he first wanted to stock the pond on his farm with frogs, he had gotten some young ones from a neighbouring farm. When he released the frogs into his pond, he was astonished to see them hop out, en mass, and begin hopping through the forest, heading back to their home-pond on the neighbour's farm! This led us to joke that once we released our home-raised frogs, we could expect them to hop to our door wanting to get back in their aquarium.

Free swimming tadpoles (two weeks old) - note the external gills

Tadpoles - 3 weeks old

In the end we released the frogs earlier than we planned due to a vacation that would have left them unattended. By this point, after 4 weeks in our care, a few of the tadpoles had begun losing their external gills and tails and had begun developing their legs. We felt a little bad when we put them back in their original pond when we noticed how much larger they were than those that had never been removed from the pond. Having read about the cannibalistic qualities of frogs, I have no doubt that our home-raised ones may terrorize their smaller, less fortunate siblings.

Releasing the tadpoles

A recent visit to the pond in June yielded a surprise - a mini highway of sorts made up of thousands and thousands of tadpoles swimming along the bottom of the pond. I had no idea that frogs or tadpoles engage in any kind of schooling behaviour. The behaviour lasted for about two weeks according to my father-in law.

Schooling tadpoles in a pond

And now it is July. The tadpoles have become frogs, and they are busy hopping all over my father-in law's farm. This being a wet summer so far in Denmark, there are plenty of insects about for them to eat. Their biggest danger is the outdoor tractor mower my father-in law uses to cut the lawn surrounding his property. I am told the smart ones duck into the grass, the lucky ones somehow pass through the blades unharmed, and the others? Well, those little bits of red sushi on the grass got there some how. The same grissly scene is repeated on local roads, as after any rain I notice hundreds of frogs hopping along the roads...

Some other Danish salamanders/newts/frogs found on my father-in law's farm...

Mystery fish found in the pond

In conclusion, I would recommend anyone who has the opportunity of raising frogs or toads from eggs to do so. You do not even need an aquarium to do it. Some Danish family members also raised frogs this year, but kept their eggs in a five gallon bucket. The tadpoles developed just fine and provided an excellent and entertaining bit of education for children. Obviously this project would be ideal for an elementary school class. The only tricky bit could be to find the frog or toad eggs in the first place.

Editor's note: I came across the following quote taken from a study on the decline of Danish frog and toad populations:

     "In Denmark we have eight different species of frogs and three species of toads, all of which
       have declined sharply in numbers over the past 50 years. The reason for this decline is
       probably mainly due to loss of habitat, but also due to deterioration in the quality of
       remaining habitats. Frogs are closely connected to the aqueous environment and are
      therefore extremely sensitive to pollution." Brande-Lavridsen