Sea Fish

Spider fish

    • Scientific name:  Trachinus draco
    • Common name:  Spider fish
    • Aquarium size:  200 liters
    • Temperament: Calm
    • Temperature:  Between 15º and 30ºC
    • pH: Between 8.2 and 8.4
    • Diet:  Carnivore
    • Length:  25 cms to 30 cms


The spider fish (Trachinus draco) is a poisonous marine fish, belonging to the Trachinidae family. Although it is not a very popular fish in home aquariums, it requires little care, which makes it very easy to keep.
They do not need an aquarium with many ornaments, they are carnivorous, sedentary, nocturnal and spend much of the day hidden under the ground.


Spiderfish have an average length of 25 to 30 centimeters, although this depends on the variety and age.

It has a fairly large mouth and head compared to its body, which is rather elongated, about six times as long as its head. Its body is narrow and somewhat flattened laterally.

Its head has a small elevation that allows it to keep an eye on its prey when it is hidden under the ground, and its eyes are quite close together, in addition, it has two small spines in front of each one.
It has two dorsal fins; Its first dorsal fin is short, generally dark or black in color and with 5 or 7 spines that are poisonous.
Its second dorsal fin has between 21 to 32 soft spines that also have venom and are its main defense against predators. Its tail fin is slightly curved.

This fish has a green hue with dark spots on the head and some blue and yellow lines on both sides. This type of coloration is called «cryptic» which means that it can blend in with the environment to go unnoticed by its enemies and prey.

Sexual Dimorphism

Both females and males of this species have the same appearance, it is practically impossible to distinguish them … therefore, there is no sexual dimorphism.

Watch out!! Spider Fish Bite

The Trachinus draco is one of the best known poisonous fish (along with the stone fish or the scorpion fish ), since it is common to see bathers and fishermen injured by bites of this fish, especially on beaches with shallow waters.
The spider fish bite is very painful and difficult to treat; in humans, it causes symptoms of inflammation, redness, vomiting, pain, fever, even reaching respiratory failure and seizures.

The pain usually subsides within 2 to 24 hours after the bite, although it should be noted that this fish is not aggressive towards humans, and that most injuries are caused when bathers accidentally step on them.or by a bad manipulation on the part of the fishermen.

Its venom is found in the spines that surround its dorsal fins. It is advisable to be very careful with its handling, since this fish remains very toxic even after its death.

Currently there is no antidote against the bite of this fish, for this reason it is important to receive medical attention immediately, since the symptoms could be complicated and trigger serious consequences, such as developing gangrene in the affected area.

Distribution and habitat

The spider fish is typical of the Mediterranean, in the Cantabrian Sea and the eastern Atlantic Ocean. The habitat is found in all areas where sandy, muddy or gravel bottoms abound , as it uses them for hiding and hunting.

They inhabit seabed at different depths, ranging from a few meters to about 150 meters deep.

During the summer, it is common to find it near the coasts and shallow beaches , since the sand simulates the habitats where it usually hunts and this because it usually causes problems with bathers.

Aquarium Conditions for Spider Fish

This fish needs an aquarium of about 200 liters of water for each specimen , with a layer of at least 10cm of fine sand and with little intense lighting since it is a fish used to living in low light.
The optimal conditions for the correct development of spiderfish in captivity are:

  • Temperature: between 15ºC to 30ºC
  • Density: 1.025 to 1.035
  • pH: 8.2 to 8.4

Nitrates up to a maximum of 60 ppm, avoiding nitrites and ammonia.

These fish are very resistant since they can withstand sudden variations in the water parameters and high levels of contamination, however, it is recommended to siphon the bottom of the aquarium, have a powerful filtration and make frequent water changes, recommended every week.


It feeds mainly on small fish that live on the seabed, as well as small crustaceans and mollusks.

In captivity, live fish food must be offered and they rarely accept frozen or dried food , and care must be taken not to overfeed as it could be detrimental to their health.

It should be fed offering small amounts of food since its digestive system cannot process a large amount of food per day and it is advisable to do it 2 to 3 times a week since being a sedentary fish, it is used to spending long moments of inactivity until waiting for a prey that can attack.

Behavior and Compatibility

The spider fish is sedentary, spending much of the day hidden underground to camouflage itself from its possible prey, waiting for the right moment to attack.
It is nocturnal and goes swimming at night, at which time it is more vulnerable to being attacked by predators, however it has several poisonous spines to defend itself.

It is aggressive towards other males of the same species and when it must defend its territory from another fish, it is also usually hostile during the mating season.

It is generally compatible with other fish that are larger and do not compete for the bottom of the aquarium, but it is not advisable to put them in the same aquarium with other fish smaller than them or of equal size, because they can end up being their prey.


Its reproduction is by external fertilization and has not yet been achieved while in captivity . The females expel the eggs and the male fertilizes them with his sperm, after three months the small fish are born that take about three more months to fully develop.
The life expectancy of this fish is not very high, between one and two years of life.

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