Coral reefs are valuable and important ecosystems. They are among the most productive and diverse of all-natural ecosystems, and they are often called «the tropical rain forests of the sea» (Bourilere and Harmelin 1989). Coral reefs have many functions, amongst which is the provision of a variety of habitats for a wealth of organisms. Fishes are a dominant group of coral reef fauna, in terms of both their biomass and diversity. They are the most visible and important mobile component in the coral reefs (Letourneur et al. 1999). Reef ecosystems provide fishes with shelter, feeding, spawning and nursery grounds. Pollution, destructive fishing, over-fishing, coral bleaching, tourism development and other stresses and activities threaten these valuable ecosystems.

While the Red Sea fish fauna is taxonomically quite well known (Randall 1992, Goren and Dor 1994, Khalaf 2004) compared with other parts of the tropical Indo-Pacific Ocean, the community structure of shore fishes has been less well investigated (Khalaf and Kochzius 2002). Despite a long tradition of taxonomical work (e.g. Forsskal 1775, Klunzinger 1884), few studies have been published on the general community structure of the Red Sea shore fishes (Bouchon-Navaro 1980, Ben-Tuvia et al. 1983, Rilov and Benayahu 2000, Khalaf and Kochzius 2002, Alwany and Stachowitsch 2007) and these studies cover a small range of spatial distribution. Most species of near-shore fishes in the Red Sea associate with coral reefs, although some occur in sea grasses, sandy areas, and other near-shore habitats (UNEP 1997). The present study was carried out through the Sustainable Use and Management of Living Marine Resources component of the Strategic Action Programme for the Red Sea and Gulf of Aden (SAP) executed by The Regional Organization for the Conservation of the Environment of the Red Sea and Gulf of Aden (PERSGA) between 1999 and 2003. The study was conducted at coral reef sites to assemble comparative regional data on the distribution of fifty ornamental fish species at latitudinal (11–29°N) spatial scales. The main objectives of the study were to assess the community structure, and biogeographic affinities of Red Sea coral reef fishes that are collected for the aquarium trade.

Figures 4, 5 and 6 illustrate differences in the mean fish abundance per 500 m² transect, according to latitudinal distribution among the 50 ornamental fish species. These belong mainly to the following fish families: [Fig. 4. I. Acanthuridae (4 species), II. Balistidae (3 species), III. Chaetodontidae (14 species), IV. Pomacanthidae (4 species)[; [Fig. 5. V. Pomacentridae (5 species), VI. Pseudochromidae (3 species), VII. Cirrhitidae (one species), VIII. Serranidae (one species) IX. Labridae (11 species)]; and Fig. 6. X. Scorpaenidae (2 species), XI. Ostraciidae (one species), XII. Tetraodontidae [(one species)] that are utilized by the aquarium trade in the region.

Acanthuridae (Surgeonfishes)

Of the 12 species of surgeonfish’s reported from the Red Sea, only 4 speciesare important in the ornamental fish trade, therefore only Acanthurus sohal, Orangespine unicornfish Naso lituratus (Forster, 1801 in Bloch and Schneider 1801), Zebrasoma veliferum and Zebrasoma xanthurum were counted. Acanthurus sohal were abundant along Egyptian latitude 27° followed by Saudi Arabian latitude 22°. Naso lituratus were abundant along the Djiboutian reefs at latitude 11° (Fig 4). Zebrasoma veliferum were abundant along the Saudi Arabian reefs at latitudes 22 and 21°. Whereas, Zebrasoma xanthurum were most abundant along the Djiboutian reefs at latitudes 11 and 12°. Triggerfishes had the lowest number of individuals.

Balistidae (Triggerfishes)

This family had the lowest number of individuals of all fish families examined here. Out of the 10 triggerfishes reported from the Red Sea, only Ornage-lined triggerfish Balistapus undulatus (Park, 1797), Titan triggerfish Balistoides viridescens (Bloch & Schneider, 1801), and Picasso triggerfish Rhinecanthus assasi (Forsskål, 1775) were counted due to their importance in the aquarium trade. Geographical trends indicated that Balistoides undulates and Balistoides viridescens were more abundant along the Saudi Arabian reefs at Latiudes 22, 21 and 20° but Rhinecanthus assasi did not show any clear geographical trend (Fig. 4).

Chaetodontidae (Butterflyfishes)

Out of the 17 butterflyfishes known from the Red Sea, this study indicates the presence of 14 species. Geographical trends were observed in almost all butterflyfish species (Fig. 4). Chaetodon austiacus and Chaetodon paucifasciatus were most abundant along the reefs at latitudes 29 and 27°. These two species were not recorded in latitudes 15, 12 and 11°. On the other hand, Chaetodon auriga, Chaetodon fasciatus and Chaetodon lineolatus Cuvier, 1831 in Cuvier and Valenciennes were most abundant along the Egyptian and Saudi Arabia at latitudes 27, 22, and 21°. Chaetodon larvatus was most abundant along the Saudi Arabia and Yemen reefs at latitudes 20 and 15°. There were 3 butterflyfish species Chaetodon melapterus, Chaetodon vagabundus, and Pennant coralfish Heniochus acuminatus (Linnaeus, 1758) exist only at the Djiboutian reefs at latitudes 12 and 11°. The distributional pattern for all butterflyfish species is shown in Fig. 4.

Pomacanthidae (Angelfishes)

This family had the second lowest number of individuals of the fish families examined here. Out of the 7 species of angelfish recorded from the Red Sea, only 4 species (Pomacanthus asfur, Emperor angelfish, Pomacanthus imperator (Bloch, 1787), Pomacanthus maculosus, and Pygoplites diacanthus) that are used in the aquarium fish trade in the Red Sea were found. Latitude 15° exhibited the highest number of individuals for angelfish species, particularly for Pomacanthus asfur and Pomacanthus maculosus. Whereas, the reefs at the latitude 29° had the lowest number of individuals. Geographical trends were clear for some species like Pomacanthus asfur which is the most abundant angelfish at the latitudes 15° but did not reach the northern Red Sea at the reefs between latitudes 29 and 27°.The distributional pattern for angelfish species is shown in Fig. 4.

Psudochromidae (Dottybacks)

Out of the 12 dottybacks fishes known from the Red Sea, only 3 species of importance in ornamental fish trade were counted. The 3 of them were not reported along the Djiboutian reefs. Bluestriped dottyback Pseudochromis springeri Lubbock, 1975 preferred the north, and it was found only along the Jordanian and Egyptian reefs at latitudes 29 and 27°. Whereas, Orchid dottyback Pseudochromis fridmani Klausewitz, 1968 extended to reach reefs at latitude 15°. The distributional pattern for Dottybacks is shown in Fig. 4.

Pomacentridae (Damselfishes)

Damselfishes had the highest number of individuals at all studied sites. Out of 35 damselfishes known from the Red Sea, only 5 species that are mostly used in the aquarium trade in the region were counted. Chromis viridis was the most dominant species of the damselfish family on Red Sea reefs. Geographical distribution of the clownfish Amphiprion bicinctus revealed that it prefers the Jordanian and Egyptian reefs at latitude 29° and 27°. The distributional pattern for damselfishes is shown in Fig. 5.

Labridae (Wrasses)

Out of the 64 wrasses reported from the Red Sea, only 11 species that are used mostly in the aquarium fish trade were counted. Thalassoma rueppellii, Bodianus anthioides (Bennett, 1832), Coris aygula Lacepède, 1801 and Anampses twistii were most abundant along the reefs in latitudes 29 and 27°; they were rare or not recorded along the Yemeni and Djiboutian reefs at latitudes 15, 12 and 11°. However, Thalassoma rueppellii and Bodianus anthioides were restricted to the northern and central Red Sea. On the other hand, Thalassoma lunare was most abundant in the south at latitudes 15, 12 and 11°.The cleaner wrasse Labroides dimidiatus wasmost abundant along the reefs in latitudes 27, 22° and Larabicus qudrilineatus on the other side was most abundant along the reefs at latitudes 15, 12 and 11°. The distributional pattern for wrasses is presented in Fig. 5.

Serranidae (Groupers)

Only Pseudanthias squampinnis belonging to the subfamily Anthininae was counted during this study. The counts indicated that this species was most abundant along the reefs at latitudes 27 and 29° respectively and it was not reported from the Yemeni and Djiboutian reefs at latitudes 15, 12 and 11° (Fig. 5).

Cirrhitidae (Hawkfishes)

Paracirrhites forsteri did not show a geographical trend in its distribution, except that it was not recorded in reefs at latitudes 29°, 15, 12 and 11° (Fig. 5).

Ostracidae (Boxfishes)

The distributional patterns for the boxfish, OstraciOstracion cubicus Linnaeus, 1758, are shown in Fig. 6. It was abundant along the Jordanian reefs at latitude 29° and Saudi Arabia 22° reefs. It was either rare or not reported in other studied sites.

Tetraodontidae (Pufferfishes)

Arothron diadematus (Rüppell, 1829) is of importance in the fish aquarium trade in the region, and the number of individuals were very low. This species was not reported in the southern Red Sea and Gulf of Aden (Fig. 6).

Scorpaenidae (Scorpionfishes)

Two species Pterois miles (Bennett, 1828) and Pterois radiata Cuvier, 1829 in Cuvier and Valenciennes 1829 belonging to this family were counted; Pterois miles was reported only on Jordanian and Egyptian reefs. Whereas, Pterois radiata reached to Djiboutian waters, but both species were present in very low numbers. The distributional pattern for both species is shown in Fig. 6.

Cluster analysis revealed that two primary groups of sites can be distinguished from the data (Fig. 7): Group A is divided into two sub-groups gathering the sites from Djibouti and Yemen with about 58% similarity: sub-group (A1) incorporates sites in Djibouti latitudes 12 and 11° with about 70% similarity (A2) incorporates sites in the country of Yemen (latitude 15°) with about 63% similarity, and sub-group. Group (B) is divided into 3 sub-groups gathering the sites in Jordan, Egypt and Saudi Arabiawith 71% similarity: subgroup (B1) incorporates the sites in Jordan latitude (29°) with about 82% similarity, subgroup (B2) incorporates most of the sites in Egypt at latitudes 27 and some sites in Saudi Arabia at latitudes (20, and 21°) with about 82% similarity., and subgroup (B3) incorporates the sites is Saudi Arabia at latitudes (21 and 22°) with about 75% similarity. These two main groups (A and B) are connected together with about 52% similarity. The data clearly show that ornamental fish communities in the Red Sea and Gulf of Aden fall into two distinct biogeographical groups. One of the groups characterizes the northern and central Red Sea, whilst the other is in the southern Red Sea and Gulf of Aden.

A new and updated checklist of fishes of the Red Sea has recorded a total of 1078 species belonging to 154 families (Golani and Bogorodsky 2010). From this list, a total of 50 fish species used for aquarium trade were investigated during the present study. A database for aquarium fish stocks was established during this intensive survey, and is housed at PERSGA office Jeddah, Saudi Arabia.

This study revealed marked differences in the structure of ornamental fish assemblages with latitude. The presence-absence data for the fifty ornamental fish species used in the aquarium trade in the region support the presence of two main biogeographic gradients in the Red Sea and Gulf of Aden: a south Red Sea and Gulf of Aden latitudinal gradient, and a gradient along the north and central Red Sea. Latitudinal gradients in water quality (temperature, salinity, plankton production) may cause in part this north-south variation in fish community structure. There are marked changes in the structure of coral reef fish communities moving from north to the south within the Red Sea. Carter and Prince (1981) concluded that gradual changes in salinity and temperature could generate abrupt boundaries for species distributions. Differences in environmental tolerance among species could mean that some are better adapted to conditions prevailing in the south than those further north or vice-versa. Factors in the physical environment including irradiance, salinity, temperature, pressure, nutrients and wastes all influence the distribution of organisms in the sea. The ability of an organism to tolerate changes in these physical environmental factors plays a major role in determining the organism’s distribution in the marine environment (Karlenskint et al. 2008). There are strong gradients from north to south in surface water temperature (approx. 6-8 °C), salinity (5–7 ppt), nutrient concentration and turbidity in the Red Sea (Gordeyeva 1970, Morcos 1970, Morley 1975, Edwards and Head 1987, Weikert 1987).

The gradient observed during this study could also be due to different types of habitat available in the different sites, as well as their different amounts of coral cover, which could produce more or less favorable conditions for the development of juvenile fishes (availability of food, food supply, substrate complexity with different coral cover, etc.). This study identified major differences in the faunal composition and relative abundance in almost all of the fish families investigated. They included the studied species of triggerfishes (Balistidae), surgeonfishes (Acanthuridae), butterflyfishes (Chaetodontidae), angelfishes (Pomacanthidae), damselfishes (Pomacentridae), Wrasses (Labridae), dottybacks (Pseudochromidae) and Pseudanthias squamipinnis in the family grouperfishes (Serranidae). Similar results were obtained by (Ormond and Edwards 1987; Roberts and Ormond 1987; Roberts et al. 1992). Sheppard et al. (1992) indicated that there are marked differences among the different regions of the Red Sea in fish species richness, assemblage composition and species abundances. Brokovich et al. (2006) reported a strong correlation between fish assemblages and the different types of habitats at the northern tip of the Gulf of Aqaba. Similar results were also reported by Khalaf and Kochzius (2002).

The fish fauna of the Djiboutian coast is shared with the Indian Ocean and the Red Sea. However, in terms of species composition, the Red Sea influence dominates, especially in areas near to Bab el Mandeb (Barrat and Medeley, 1990). A biogeographic analysis of the Indian Ocean coral fauna based on presence/absence of species revealed a clear pattern of faunal relationships between the Red Sea, Southern Arabia and the Indian Ocean (Khalaf and Kochzius 2002). Habitat strongly influences which species are able to live in a particular place. There are considerable differences in reef structure and coral assemblages from north to south within the Red Sea. In the south, reef structures becomes shallow with macroalgal dominated frameworks (Yemen and Djibouti). In the far south there are few areas of hard substrata, and these are mainly coralline-algal reefs covered with dense growth of the brown algae Sargassum and Turbinaria (Khalaf, personal observation).

A review of the literature describing fish habitat correlations from various regions presents a convincing positive relationship between habitat structural complexity and reef fish diversity in the Caribbean (Risk 1972, Luckhurst and Luckhurst 1978) and in the Great Barrier Reef (McCormick 1994). The strength of this correlation however, may vary among reef types. Percent of live branching or massive coral, substratum diversity and complexity have several times been identified as important predictors of the diversity of reef fish assemblages (Talbot 1965, Talbot and Goldman 1972, Luckhurst and Luckhurst 1978, Bouchon-Navaro and Bouchon 1989). This study supports the above mentioned studies, and shows that a number of fish species occupy different latitudes. Species varied in their abundances from reef to reef, and adjacent reefs supported different groups of species. As a general conclusion, we suggest that differences among reefs and habitats were among important components of variability in the number of fishes and species of ornamental fishes along the Red Sea and Gulf of Aden.

The high numbers of the clownfish Amphiprion bicinctus along the Jordanian reefs at latitude 29° compared to other reefs in other latitudes is perhaps due the availability of the sea anemone hosts Entacmaea quadricolor and Heteractis crispa (Huebner et al. 2012). Chadwick and Arvedlund (2005) proposed that Heteractis crispa may serve as nursery habitats for Amphiprion bicinctus because they host more juvenile fish than does Entacmaea quadricolor, and Huebner et al. (2012) further documented this relationship using field experiments. The present study revealed that Amphiprion bicinctus, which is an endemic species to the Red Sea and Gulf of Aden, was a common and abundant species in the northern Red Sea, less common in the central Red Sea and rare or not present in the southern Red Sea and Gulf of Aden. These patterns may be due in part to the distributional and abundance patterns of the above host anemones, but detailed surveys of these anemones need to be conducted throughout the Red Sea to further test these ideas.

Two of the 3 species that belong to the family of dottybacks, Pseudochromidae i.e., Pseudochromis springeri and Pseudochromis fridmani were endemic to the Red Sea (Randall 1992), and both of them were not found along the Yemeni and Djiboutian reefs. The third species Pseudochromis flavivertex which is endemic to the Red Sea and Gulf of Aden (Randall 1992) was recorded in all latitudes except at latitudes 12 and 11° along the Djiboutian reefs during this investigation. A total of 14 butterflyfishes are reported from the Red Sea, of which seven are endemic or range no further than the Gulf of Aden (Randall, 1992). In the present study, 14 species of butterflyfishes have also been reported. Butterflyfish assemblages in the southern Red Sea differ from that in the north (Righton et al. 1996). Other differences occur among butterflyfish. For example, Chaetodon paucifasciatus is abundant in the Gulf of Aqaba and Gulf of Suez but absent or rare in the southern Red Sea. However, Chaetodon larvatus is a dominant species in the south but rare in the northern Red Sea and Gulf of Suez and absent entirely from the Gulf of Aqaba. On the other hand, there are some species such as Heniochus acuminatus, Chaetodon melapterus and Chaetodon vagabundus that are present along the Djiboutian reefs but are not reported in the Red Sea. The results presented in this study demonstrate that there are many differences between the reef fish fauna of the northern and central Red Sea, from that of the southern Red Sea and Gulf of Aden. For example, Pseudanthias squamipinnis dominated fish assemblages in the northern Red Sea along the Jordanian and Egyptian coasts, whereas Chromis viridis dominated fish assemblages in the central Red Sea, along the Saudi Arabia coast at both latitudes 20 and 21°, and in the Gulf of Aden.

During this survey, Chromis viridis was the most abundant species in the Red Sea and Gulf of Aden. This species dominated the reefs at latitudes 21, 20, 15, 12 and 11°. Similar results were reported at Nuweiba (Ben-Tuvia, 1983), at Djiboutian reefs (Barrat and Medley 1990), at Sanganeb atoll (Krupp et al. 1993), and in Eritrean reefs (Daw et al. 2001). Chromis viridis usually forms large aggregations and is found associated with large heads of Acropora corals that provide shelter from predators and a nocturnal retreat. Thus, these distributional patterns for this fish may indicate a higher abundance of large Acropora corals on southern than northern reefs in this region. The second most abundant species was Pseudanthias squamipinnis, which dominates the reefs at latitudes 29, 27 and 22°. Similar findings were recorded at the Japanese Garden reef site at Eilat (Rilov and Benayahu 2000), at Nuweiba (Ben-Tuvia et al. 1983), at Sanganeb Atoll (Krupp et al. 1993), and on Jordanian reefs (Khalaf and Kochzius 2002). This species occurs usually in small to very large aggregations around rock or coral heads. These two species feed on plankton above rich beds of live coral (Khalaf and Disi 1997). These patterns indicate the importance of live coral cover, reef rugosity, and availability of plankton in the distribution of these reef fishes.