At the end of January 2015, there was a convention at Burgers’ Zoo of nutritional experts from European zoos. One of the lectures during the convention had the title above and was presented by biologist Max Janse, the Head of the Ocean. In the presentation, an overview was given on how feeding sharks and rays takes place within the world of zoos. This is something that occupies a lot of our time at the Ocean, because it is directly linked to the health of the animals.
What kind of answer would a shark give?
Sharks are carnivores, a nice word for meat-eaters, in this case fish-eaters. But what do they actually eat in the wild and what should they be fed in an aquarium? It is not such a simple question. There have been many scientific studies into the behaviour of sharks in the wild as well as examinations of the content of their stomachs. The result has been that every species of shark has its own diet, which even changes as the shark grows. Some species of shark are specialists and have specialised teeth for opening shellfish and molluscs, while others are opportunists: they eat whatever swims in front of their faces. How does this information help us? On the one hand, you can consider the kind of food you are providing, on the other, it is all a matter of trial and error.
The policy at Burgers’ Zoo is to feed sharks live food. This is an ethical question, but also very practical. It is actually quite difficult to always have live food on hand. You also cannot be sure whether the shark has eaten it or not if it does not eat during the monitored times. This makes the
choice simpler: frozen food. It is easy to store, available in many forms, of good quality, and can also be broken into bite-size pieces. A large freezer in the Ocean is loaded with all types of fish, squid, prawns, and mussels. A shark that is new to the Ocean will first be placed in quarantine behind closed doors. There, it will be offered various types of food in order to see whether it wants to eat at all and what its general preferences are. We will then teach the animal to eat at a certain location and to eat from tongs or forceps. These lessons can last from weeks to even months. Once the shark has passed these classes, it can be moved to the aquarium. In the aquarium, all sharks and rays are fed individually.
Sharks can become overweight if fed too much. Sharks have a special mechanism, which stores excess fat in the liver. This increases their capacity to float, but if too much fat is stored, it can cause liver problems. It is fairly difficult to know how much you should feed a shark per day. For this, we use information from scientific research on growth and nutrition. Within the aquarium world, there are existing nutrition guidelines to be followed, which are expressed in the percentage of the shark’s body weight. For instance, if a shark weighs 10 kilos, it receives 8% of its body weight in food each week—800 grams. This percentage depends on the species, the lifestyle, and the age. Some young sharks are captured to see if they are growing as quickly as they would in nature. Additionally, the professional observations of the caretaker are very important. How the animal responds, how quickly it eats, how it looks, etc.—the list goes on. Adult sharks do not have to be fed every day; three to four times a week is plenty. In nature that sometimes occurs less, but it is better not to leave the sharks hungry so that their aquarium flatmates do not get attacked.
If you feed the animals individually, it is also possible to add extra things to their feed, such as medication, minerals, or vitamin tablets. There is always some vitamin loss in the feed, because it has been frozen, but also because it is cut into pieces. This is why the vitamins lost are added to the feed as pills each week. Furthermore, variation in the feed is very important. Monday is mackerel day, Wednesdays are herring, and the sharks get squid on Fridays. On the weekends, coalfish or haddock are on the menu. The sharks do not always appreciate the latter. But since they are required to clean their
plates, the weekend creates a balanced diet for the animals.