The dusky spinefoot ( Siganus luridus), also known as the squaretail rabbitfish, is a species of marine ray-finned fish, a rabbitfish belonging to the family Siganidae. It is native to the western Indian Ocean which has spread to the Mediterranean Sea through the Suez Canal (Lessepsian migration). Its fin spines contain venom. It is regarded as a food fish.
Taxonomy
The dusky spinefoot was first formally described in 1829 as
Amphacanthus luridus by the German
naturalist and
explorer Eduard Rüppell with the type locality given as the
Red Sea.
The specific name
luridus means "pale yellow", this name was given to it by the collector of the
type specimen, Christian Gottfried Ehrenberg, According to Achille Valenciennes in 1835, Ehrenberg described the colour of the body as yellowish-brown, with numerous very thin pale yellow lines. However, Rüppell said that the colour was bluish black with some irregular, paler spots and a yellowish ring around pupil in his description.
Description
The dusky spinefoot has a compressed body which Has a depth which fits into its standard length 2.1 to 2.8 times. There is a single row of
incisor-like teeth in the jaws, each with 1 or 2 lateral cusps.
The
dorsal fin contains 13-14 spines and 10 soft rays while the
anal fin has 7 spines and 9 soft rays.
[ The caudal fin is truncate.][ This species attains a maximum total length of , although is more typical.][ The colour is variable, it is normally olive green to dark brown with a mottled pattern. The are hyaline-yellow and there are dark bars on the caudal fin][
]
Distribution and habitat
The dusky spinefoot is found on the coast of eastern Africa from Mozambique northwards into the Red Sea, and also the Comoros, Madagascar, and the Mascarene Islands. Its presence in the Persian Gulf needs to be confirmed.
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It is found at depths between in waters over hard substrates, such as coral and rocky reefs.
Biology
The dusky spinefoot spawns in April and from June to August when the seawater temperature is between , the eggs and larvae are planktonic. The larvae stay close to the surface where they feed on phytoplankton and zooplankton from 3 days old. The adults are herbivores which are active during the day, hiding in cavities during the hours of darkness. They are frequently encountered in schools but solitary individuals can also be seen, grazing on algae from the substrate. It feeds on larger brown algae species, as well as other macrophytes.
Venom
This species produces venom in the spines of its fins.[ In a study of the venom of a congener it was found that rabbitfish venom was similar to the venom of stonefishes.][
]
Predators and parasites
The venomous spines are used for defence against predators so the highest predation pressure is on the planktonic and larval stages.[ Known parasites of the dusky spinefoot included the Monogenea Glyphidohaptor plectocirra and Tetrancistrum polymorphum as well as the Digenea Hexangium brayi, Hexangium sigani and Progyliauchen magnacetabulum.]
Utilisation
The dusky spinefoot is caught using set , and beach Seine net, the catch is sold as fresh fish. This species has become an important species for fisheries in the Mediterranean while i other areas, such as Kenya, it is a bycatch.
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