Zoöp Observations: Rudd on terrace deckZoöp Observations: Rudd on terrace deck

The presence of blue herons in and around the large pond of the Nieuwe Instituut makes it clear that there must be fish, I wrote in an earlier blog. This should not come as a surprise, because in November last year about 1000 rudd and perch were released in the pond, mainly to combat filamentous algae. But once released, those rudds and perches of course immediately disappeared.

In winter, many fish species live a secluded life. They seek out deeper places in ditches and ponds, where the water temperature is fairly constant and they need to use little energy. But now that spring has arrived, fish are becoming active again. Birds that like to eat fish know this. In addition to the blue heron, I also saw a cormorant spying for fish, sitting on the pond statue of Auke de Vries (March 13).

A few days later (March 19) Richard from the café saw a fish lying on the terrace deck of the Nieuwe Instituut. Judging by its injuries, the animal had clearly fallen prey to a heron, but by any luck did not end up in the bird's stomach. A heron usually swallows a fish headfirst, so it will slide down the throat smoothly. If a fish is not caught in the right position it is thrown up in the air and caught again. That is probably what went wrong here. The fish is a common rudd (Scardinius erythrophthalmus). The red pelvic, anal and caudal fins, the pale yellow eyes and the number of scales on the lateral stripe leave no room for misunderstanding. Richard put the rudd, which was still alive, back in the pond. After half a minute of gaining strength, it swam away.

Today I also found a fish on the terrace deck, or rather its skeleton. This fish clearly couldn't have fallen prey to a heron or cormorant, as these birds swallow their prey whole and don't eat it off the bone. So here’s the question, then: how did this fish come to its end and who did it serve as food?