Scientific Name:

Siganus luridus

Common Name:

Dusky spinefoot

Taxonomic Group:

Fishes

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Information

Key Identifying Features

The body is deep, ellipsoid, and compressed; the scales are small and embedded in the skin. The maximum length reported is 30 cm (total length; commonly 5–20 cm).The dorsal fin (13–14 spines and 10 soft rays) begins above the pectoral fin base. The pelvic fin begins behind the pectoral fin base, and its inner spine is connected by a membrane to the abdomen. The anal fin (7 spines, 9 soft rays) begins beneath the 8th to 10th dorsal spines and has a rounded margin. The caudal fin is truncated. The anterior spines of the median fins are slender and sharp, and the posterior spines are stout; all the spines are venomous. The anterior nostril has a long, broad flap covering the posterior nostril when depressed. The mouth is small with distinct lips. The maxilla does not reach the vertical plane through the eye. The incisor teeth are in a single row. The colour is dark brown to olive green with a touch of yellow on the fins, but varies regionally. At night, the colour is very mottled.

Identification and Habitat

It occurs in small schools in shallow water close to the bottom. It prefers hard bottoms of compacted sand with rock, usually covered with vegetation. The adults are solitary but groups of 3 or 4 adults have also been observed; the juveniles form larger schools. However, huge schools of adults (up to 5,000 individuals) are sometimes observed along the Mediterranean coast. It feeds on a wide range of benthic algae, mainly coarse brown algae, but seagrasses are also reported in its diet. Siganus luridus feeds at more or less the same rate in all seasons. It may suddenly stop and erect its fins (dorsal, anal and pelvic), presenting an encircling array of venomous spines to potential predators.

Similar Species Description

Two species of the rabbitfish family Siganidae are now present in the Mediterranean, both having arrived via the Suez Canal. Siganus rivulatus, the marbled spinefoot, can be distinguished by its forked caudal fin. Their diets overlap considerably. Both these rabbitfish also share a common habitat and diet with the native herbivorous fish Sarpa salpa, the salema. The salema has characteristic horizontal yellow lines on its body, yellow circles round its eyes, and a black dot at the base of the pectoral fins.

Siganus luridus Similar Species (0010) EN — **Siganus rivulatus**

Similar Species

Scientific Name: Siganus rivulatus

Common Name: Marbled spinefoot

Taxonomic Group: Fishes

History and Route of Introduction

The dusky spinefoot is a species usually found in the western Indian Ocean and Red Sea. It was first recorded in the Mediterranean in 1956 along the Israeli coast and progressively continued its geographical expansion through the eastern Mediterranean. In 2008, two specimens were caught along the French Mediterranean coast at a depth of about 5-10 m in a site mostly characterized by rocky bottoms mixed with Posidonia oceanica beds. In 2010, it was also recorded in two different localities in the Adriatic Sea (Gulf of Trieste and southern Adriatic Sea, island of Mljet). Several specimens were also observed and photographed in France close to the Italian border between November 2011 and July 2012.

Ecological Impacts

The two species belonging to the Siganidae family, Siganus luridus and S. rivulatus, have become very common in most parts of the eastern Mediterranean and strongly interact with native herbivorous fish species through competition for food resources and habitat. The spread of these two herbivorous species can result in a drastic decrease in seaweed formations. Some of these, such as Cystoseira spp. forests, are ecologically very important as nurseries for a number of littoral fish species. These Cystoseira forests are currently considered to be a threatened habitat in several regions of the Western Mediterranean. It will therefore be crucial to monitor the establishment of rabbitfish assemblages in the Western Mediterranean in the future.

Economic Impacts

Due to its great abundance in the Eastern Mediterranean, the dusky spinefoot is regularly caught by small-scale professional and non-professional fishers. However, it is of low commercial value.

Management Options

Suggested control measures are a) early eradication of new populations by MPA technicians through spear fishing, and b) maintenance of healthy and abundant predator assemblages to encourage natural control through predation.