A common fish

The five- bearded rockling is a common fish in inshore waters. It prefers areas with mud, shells, and stones. They can be very abundant on dikes and other submerged manmade structures. In fyke-nets, which we use at the NIOZ in the Western Wadden Sea, we only catch migrating fish like these rocklings in the autumn and spring, i.e. when they leave the Wadden Sea for spawning and return for food, which consists of shrimps and small fishes.

The rockling family belongs to the order of the cod-like fishes, which all have three dorsal fins. In this species the first dorsal consists of only one fin ray, followed by 50-60 very tiny rays found in a groove on the back of the fish. The third dorsal fin is long and looks normal as it is connected by a membrane. Most of the cod-like fishes have a barbell with taste organs on their chin, helping them to detect their prey even in murky waters. The rocklings have more than one barbell, which also gives them their name. So the five-bearded rockling has five barbells, the three-bearded rockling has three, and so on. The five-bearded has one on the chin, two in front of the upper lip, and two near the nostrils.

Mackerel midge

The five-bearded rockling spawns in the North Sea in winter in waters of approximately 10 metres depth. In spring the young then move to the upper layers of the water column and beaches for food, which is more abundant in shallow warmer waters. They change to a form you would hardly recognise as a rockling, living in the water column, with a silvery belly and sides, and mottled green back like a mackerel. These small fish are called mackerel-midge and are, abundant as they are, eaten in large quantities by sea birds such as terns. In late spring and summer they change colours, go towards the seabed and migrate to the Wadden Sea.

So there is a lot of migrating going on for these fish: up and down in the water column and to and from between shallow and deeper waters, as well as to the Wadden Sea and back.