NMFRI Gdynia Aquarium

Akwarium Gdyńskie

Electric eel

Electrophorus electricus

Order: Gymnotiformes | Family: Gymnotidae

This fish is commonly known as the electric eel. The name comes from the characteristic body shape that resembles an eel, but this fish is actually more closely related to the families Cyprindae and Siluriformes. These fish can be found in the waters of the Amazon River and the Orinoco River. They live in muddy currents enriched in salts and minerals that conduct electricity really well.

They have a positive charge near their head and a negative one close to their tail end. They produce an electric charge at the front of their body that comes back through the water to the tail. This creates a closed circuit that has the shape of an electric cloud which paralyzes or kills everything around.

There are electrolytes on the body of this fish, which receive electric stimuli from their surroundings. This is called electroreception. With the use of their special Hunter and Sachs organs, they send two types of electric discharges. Sachs’ organ is used as radar for electrolocation. The lower voltage of this organ helps them move through the muddy waters, which is especially useful because they lose their sight with age. Sachs’ organ is also used for sensing potential prey and partially blinding it, if the prey is small. This organ also plays a major role in finding a partner. When attacking larger prey, the eel activates Hunter’s organ, which produces a stronger discharge.

This fish can regulate the strength of discharges according to its needs and the size of the prey. The strongest discharge ever captured was in a zoo in the United States and measured 600 V.

2017-08-04
Black long spine urchin

Diadema setosum

The Black long spine urchin is mainly found in shallow waters from 1 to 6 m, however it has been observed at depths up to 70 m. It lives on various types of soil, most often on rocky shores and dying coral reefs. It feeds on small algae, which it scrapes with five chisel teeth placed in the mouth opening on the underside of the body. This species has characteristic sharp spines ending with venom glands. On the dorsal side of the sea urchin an anus is placed, marked with interesting colours. Despite their inhospitable appearance, spines are a haven for animals. Razorfishes suspended in water vertically, head down, thus protect themselves from larger predators. A prick of a spike causes a very painful wound and an itchy rash. These symptoms disappear after a few hours, but removing spines from the skin is very difficult, while leaving residue can cause infection.

2017-08-01
Red lionfish

Order: Scorpaeniformes

Family: Scorpaenidae (scorpionfish)

Pterois volitans

The Red lionfish inhabits the western Pacific, from southern Japan to Australia and the Philippines. Occurs on the hard bottom on the outskirts of reefs and lagoons. It can be found already at the water surface and at a depth of 175 meters. This fish lives about 10 years, reaching a body length of up to 30 cm. Its food are crustaceans and fish. The Red lionfish uses different strategies for obtaining food. Due to the fact that its swim bladder is surrounded by special muscles, it can control her level in the water column and change the center of gravity of the body so as to take a precise position before attacking the victim. In addition, it flushes invertebrates from the bottom using pectoral fins. Additional muscles around the swim bladder also allow it to turn upside down and freeze under the rock shelves, where it waits for the victim. It is mainly active at night and usually hides during the day.

After eating a large meal, its stomach can increase up to 30-fold, thanks to which it is able to fast for several weeks.

It leads a solitary life. Schools of up to 8 individuals gather only for breeding purposes. The female can lay up to 15,000 eggs, and its pelagic larvae can travel long distances, e.g. eggs laid in the Bahamas can reach New England along with the Gulf Stream. It has a characteristic white-red-black coloration that adapts to the surroundings. The bright stripes on her body signify that it’s dangerous. At the base of each stiff ray of its fins is a gland with a venom, except for the caudal fin. The venom contains neurotoxin, which, if pricked, can lead to death. It is a commercial species. It is consumed after removing the fins with the poison, the meat is a delicacy.

The Red lionfish as an invasive species

It is the only alien species that managed to survive in the waters of the West Atlantic. Adult lionfish occur along the east coast of the USA from Cape Hatteras in North Carolina to Florida, Bermuda, Bahamas and the entire Caribbean, as well as in the Gulf of Mexico. Its expansion began in 1985 in Florida, most likely it was thrown into the ocean from a home aquarium. Currently, the highest density of P. volitans has been observed in the Bahamas. Its numbers are several times higher than in its natural environment. In this area it was observed at a depth of 300 meters. Its body length is greater than that of individuals from the natural environment and reaches up to 50 cm. Its food consists mainly of fish, which are also food for economically important species of Atlantic fish. Another problem is the fact that it is more voracious than native predators of similar size. One Red lionfish can eat more than 20 young fish in just half an hour, very often eating the juvenile forms of important species of reef fish, such as parrotfish, which is responsible for maintaining the proper functioning of coral reefs. The Red lionfish has all the features necessary for the successful colonization of new areas. It is characterized by high competitive ability, low susceptibility to parasites, high reproductive rates, rapid growth, effective food acquisition, the presence of venom spines protecting it from predators and adaptation to any habitat.

2017-07-31
Australian marbled catshark

order: Carcharhiniformes
family: Scyliorhinidae

Atelomycterus macleayi

It is a poorly known endemic species of northwestern Australia, inhabiting coastal areas from Port Hedland in the west to Melville Island in the north. It lives in shallow waters up to 4 meters deep, although it can also be found at greater depths. It is closely associated with the bottom. It prefers a sandy bottom or covered with rocks, among which it looks for shelter. This is one of the smaller sharks, the maximum total length of his body is 60 cm. Its diet includes polychaetes, molluscs, crustaceans and small fish. It has a rounded muzzle, and its slender, brown body is covered with wide, gray stripes separated from each other by light areas. Very often the dark areas are outlined with numerous black dots that can merge and form an irregular line. Juveniles have a simpler pattern, only with broad dark stripes. It has no commercial value. As it is associated with the bottom habitat, it is not caught as a by-catch in commercial fishing.

What does reproduction of the marbled shark look like?

This question will be answered by our aquarists who deal with these sharks on a daily basis. It is our pride that the marbled shark successfully breed in the Gdynia Aquarium. Below we present the backstage of courtship and efforts of aquarists to ensure that the incubation of the embryo in the egg proceeds correctly.

The courtship and fertilization take place in the exhibition tanks. Courtship is very violent and looks almost brutal. The male chases his partner, bites her and tries to knock her over.

„This pursuit can be observed during the day, but the act of fertilization itself takes place at night. During the reproductive cycle, the female lays 2 eggs daily. We harvest the newly laid eggs and transfer them to breeding tanks in which conditions are suitable for their incubation. The tanks have special racks to which we attach eggs with their tacking barbles. It is also important that water flows around the eggs, as it washes and oxygenates them at the same time. After about 50 days, the eggs are gently “unsealed”, then the embryo is no longer tightly closed in its shell. Thanks to this unsealing, it lives and functions in the water that surrounds it (therefore it is vital to regularly replace water!). Incubation lasts about 90-100 days. At the end of the incubation period, the young shark ceases to fit in its shelter. The capsule is drilled and bitten. If it won’t be able to get out of the egg, it may end in death for small shark, so it’s important to watch it closely at this time. Often the young hatch with the remains of the yolk sac attached to the abdomen, which will be absorbed within a few days. During hatching, young marbled sharks are about 10 cm long. We transfer the newly born individuals to another tank. Each litter has its own tank, thanks to which we avoid situations in which older and stronger individuals would steal food from younger and weaker ones. We begin feeding attempts by giving them zooplanktonic animals, first living, then frozen. The next step is to try to give them clams, shrimps and chopped fish. The juveniles have special hiding places in their tanks. As a secretive species they need this kind of places.”

2017-07-31
Sea goldie

Pseudanthias squamipinnis

The Sea goldies are found in large clusters around reefs. They can often be found near shipwrecks. Antias changes sex, which – according to the observations of biologists – is not uncommon among marine fish. All Sea goldies start their lives as females. As they grow up, some of them become males and form specific harems. When a male dies, within three days the strongest female can change sex to replace him. This is a phenomenon called protogyny. Some individuals change sex and become males as they mature. You can notice a pronounced sexual dimorphism; the male reaches 15 cm and is the color of fuchsia, while the females are two times smaller and are colored orange.

2017-07-31
Tridacna maxima

The mollusc still considered relatively abundant from the Red Sea and the coast of eastern Africa, through the Indo-Pacific to the Eastern Pacific. It is listed in Appendix II of CITES. It reaches a maximum size of 40 cm.

2017-07-28