Ichthyology

Research

Scientific activities in the fish section focus on two areas:

  1. Taxonomy, systematics and zoogeography of marine fishes of the North-western Indian Ocean and freshwater fishes of South-west Asia (Research Area I Biodiversity, Systematics and Evolution);  
  2. Biodiversity and environmental research (Research Area II Biodiversity and Environment).

Littoral fishes of the Arabian Seas Region

The Arabian Seas Region, consisting of the Red Sea, the Gulf of Aden, the Arabian Sea, the Gulf of Oman and the Persian/Arabian Gulf (the Gulf), are a biogeographic subunit within the Indian Ocean. According to our present knowledge, some 2000 fish species occur in this region. Research activities in the fish section include an inventory and taxonomic revision of coastal fishes. A zoogeographic analysis is based on this revision. Research in taxonomy and systematics includes comparative morphology and molecular genetic methods.

The geographic focus of research activities and collections is the Western Indian Ocean. The two semi-enclosed northern extensions of the Indian Ocean, the Red Sea and the Gulf with their unique hydrographic conditions and palaeogeographic history, where genetic isolation of organisms increases gradually from south to north, are models for studies of marine biogeography and evolutionary biology.

Deep-sea fishes of the Red Sea and the Gulf of Aden

Hydrographic conditions in the Gulf of Aden are quite similar to those in other parts of the Indian Ocean and the deep-sea fish fauna is characterized by cold stenotherm species, while in the Red Sea hydrographic conditions combined with a high degree of isolation from the Indian Ocean result in a secondary deep-sea fish fauna, which is derived from shallow water species. Diversity is fairly low and the degree of endemism (species which occur only here and nowhere else) is very high. Against this background, the diversity of deep-sea fishes is described, patterns of vertical distribution assessed and ecological groups defined as the baseline for zoogeographical analyses. These studies, which were initiated by W. Klausewitz and his collaborators, are continued by Uwe Zajonz. They are based on a taxonomic revision of the deep-sea fishes of the area. A total of 157 species in 118 genera and 73 families were recorded from the Red Sea, while 340 species in 212 genera and 105 families are known from the Gulf of Aden.

The vertical distribution of each species is mapped and the fish diversity for each depth range assessed. Considering biological and ecological data, ecological groups are defined and the vertical zonation is described using explorative cluster analysis. In the Red Sea, fish population densities decrease with increasing depth. Species diversity is dominated by eel-like fishes (Anguilliformes) with a high number of endemics. According to our present knowledge, 44 species occur exclusively in the Red Sea, which corresponds to an endemism of 28 %.

Population dynamics of reef fishes

Besides taxonomic research, field studies of reef fishes are an important part of the fish section’s activities. Over extended periods of time reef fishes are counted by species along underwater transect lines and long-term dynamics of fish populations are documented and analysed. Thus far, these studies were undertaken in the Gulf of Aqaba, the Sudanese Red Sea, Socotra Archipelago and the Gulf.

Population studies of reef fishes undertaken in the Gulf since 1991 are of particular interest, because they reveal the effects of catastrophic events on fish assemblages. The Gulf War oil spill caused only temporary damage and fish populations recovered after about three years.  The effects of coral bleaching since 1996, attributed to increased sea surface temperatures and followed by a large-scale coral die-off, were much more dramatic. These events resulted in a decline in the number of species per surface unit and a shift in species composition: in some of the dead reefs, obligatory coral associated species disappeared.

With a delay of about two years following the first major coral bleaching event, a decline in reef fish assemblages was observed. Strictly coral associated species, like the Arabian butterflyfish (Chaetodon melapterus) were most severely affected, while population densities of the Arabian surgeonfish (Acanthurus sohal), a species which feeds on algae in shallow waters, increased.

Taxonomy and zoogeography of Middle Eastern freshwater fishes

Globally, the Middle East is the only transition zone between three major biogeographic units, the Palaearctic, the Afrotropical and the Oriental realms. Since the Miocene a faunal exchange took place in this region via ever changing river networks. With increasing aridity since the late Miocene, river courses were isolated from each other. Research activities focus on the reconstruction of pathways of migration, which fish populations used in a faunal exchange between Europe, Asia and Africa via the Middle Eastern land bridge and speciation processes in this transition and retraction zone as a result of increased fragmentation of river systems. At present taxonomic revisions, mapping of distribution patterns and zoogeographic analyses focus on the Arabian Peninsula.

Identification guides for fisheries purposes

With a horizontal and vertical extension of fishing grounds and a diversification in species compositions of catches and landings, the marine environment is increasingly threatened by unsustainable fisheries practices. Against this background there is an urgent need of taxonomic expertise for fisheries planning and management. Since many years the fish section cooperates with the biotaxonomic programme of the Food and Agriculture Organization (FAO) of the United Nations, making available the results of taxonomic baseline research for the requirements of fisheries management and marine environmental conservation. With the joint project “Species Identification Guide for Fishery Purposes, Eastern Central Pacific” FAO and Senckenberg replied to a request by the governments of Central American states, who urgently needed an identification guide for the planning and management of their fisheries. A guide book of three volumes and more than 1800 pages was produced, which for the first time provided illustrated identification keys and descriptions of all marine species of potential economic and/or environmental importance from macroalgae to marine mammals. Previously there had only been scattered, largely unpublished information of limited reliability. More than 60 taxonomists contributed original information to these books. The manuscripts were tested in the field in Central America for completeness and accuracy of the keys. These field exercises were combined with training of regional fisheries biologists in the use of identification keys and the collection of reliable fisheries data at the species level.

Subsequently, an identification guide to the marine flora and fauna of the Persian/Arabian Gulf was produced. For the first time all fish species known from the Gulf were briefly described and illustrated.