Fishes of the Month

Found in brooks, swamps, pools and streams in humid forested and highland savannah and rainforests of Cameroon and Nigeria. The species has evolved a semi-annual spawning strategy to adapt to the unpredictable nature of the freshwater ecosystems within which it is found. This means that the eggs can survive a period of drying as well as being viable when permanently submerged. It is a bottom spawner and has a one-month incubation period. The species is assessed as Least Concern ( https://www.iucnredlist.org/species/182030/134759395) by IUCN Red List of Threatened Species™ although there are a number of threats that may be significant declines across its range including shifting agriculture, logging and urban development.

The Mangarahara cichlid or joba mena, Ptychochromis insolitus, is endemic to the Sofia River catchment of Madagascar.  The species is assessed as Critically Endangered by IUCN Red List of Threatened Species™ due to its small range, declining population, and threats from loss of habitat and loss of water caused by upstream dams.  The species received global attention in 2013 when London Zoo launched a global search for a girlfriend for their two male fishes in a bid to start a conservation breeding programme. Captive populations have since significantly increased, and captive bred individuals can now be found in 23 institutions globally. This is particularly important as the situation in the wild has further declined. In 2013, a survey of the Amboaboa river near Marotandrano found a small population of the Mangarahara cichlid, however, a survey of the same river in 2024 found no evidence of the species.

The Acıgöl killifish, Anatolichthys transgrediens is endemic to Lake Acıgöl, Southwest Turkey. The lake is approximately 35m² and is known as the ‘bitter’ lake due to the high sulphate springs that feed into it. The killifish is currently classified as Critically Endangered by the IUCN Red List of Threated Species ™ due to its limited range. Invasive species such as the Mosquitofish, Gambusia holbrooki, salt mining, pollution, and agricultural practices have been the main pressures on this species and its habitat. In June 2024, the Acıgöl killifish was given an IUCN Green Status of Critically Depleted with a Species Recovery Score of 15%. The Turkish Ministry of Agriculture and Forestry, Hacettepe University and Istanbul Aquarium relocated a population from Lake Acıgöl to Istanbul Aquarium in Sept 2024 to safeguard this species in an ex-situ capacity. This killifish is a priority within the EAZA Cyprinodontidae and Aphaniidae European Endangered Programme (EEP) and is currently cared for in several zoos and aquariums in Europe. Collaborations between Turkish institutions and European Zoos and Aquariums are crucial to protect these insurance populations as their wild counterparts could be lost forever.

Nominated by FFSG Member Alex Cliffe

The Zeravshan dace, Leuciscus lehmanni, is a native freshwater fish species endemic to the Zeravshan and Amu Darya drainages, part of the Aral Sea Basin in Central Asia including Uzbekistan, Tajikistan and Turkmenistan. Morphologically, it is characterized by dorsal fin rays numbering III 7-8, anal fin rays III 8-10, and lateral line scales ranging from 42 to 48. The species exhibits a maximum recorded size of 22 cm in length and 160 g in weight. Its distribution, biology, and ecology remain poorly studied, but it is known to inhabit lowland and foothill regions of the Zeravshan River, typically in areas with slow-flowing water and substrates dominated by mid-sized rocks. It coexists with other native fish species, including Capoeta heratensis, Schizothorax fedtschenkoi, and Triplophysa uranoscopus. The Zeravshan dace is primarily algivorous, feeding on algae, but also consumes insect larvae.

The species faces significant threats from anthropogenic activities, including damming, habitat alteration, and the introduction of invasive fish species. Additionally, extensive soil excavation in the Zeravshan River basin has led to the degradation and destruction of its suitable habitats. Due to limited research and ecological data, the conservation status and population trends of the Zeravshan dace remain uncertain, necessitating further studies to inform effective management and protection strategies.

Nominated by FFSG Member Akbarjon Rozimov, Uzbekistan

Image © Yuri Borba

The Barred Tail Pearlfish, Notholebias minimus, a threatened species of South American Killifish (Rivulidae), inhabits temporary wetlands in the Atlantic Forest biome, in the coastal plains of the southeastern region of Brazil, in the State of Rio de Janeiro. Its distribution is limited to areas west of Guanabara Bay, ranging from the Jacarepaguá Lagoon System to the Guarda River basin, in the municipalities of Rio de Janeiro, Seropédica, and Itaguaí. The species, like most annual Killifish, has a restricted geographic distribution, low dispersal capacity, small body size, rapid growth, pronounced sexual dimorphism, and a life cycle synchronized with the rainy season. During the dry season, the eggs in the substrate remain in embryonic diapause, awaiting the next rainy season to initiate the life cycle at the onset of the rains. The species is assessed as Endangered by the IUCN Red List of Threatened Species™. Agricultural expansion and unplanned urban sprawl are the primary causes of significant population declines across the species’ distribution, due to habitat fragmentation, landfilling, cattle grazing, pesticide use, and draining of wetlands. However, countermeasures are being taken to conserve this species. It is included in the Brazilian National Action Plan for the protection and development of strategies for the conservation of endangered species of the Rivulidae family, known as the “PAN Rivulídeos” of the Chico Mendes Institute for Biodiversity Conservation (ICMBio), linked to the Ministry of the Environment.

Nominated by FFSG Members Carlos H. P. Luz, and Paulo A. Buckup, Brazil

Images © Paul Loiselle

In honour of our Late Chair Dr Paul V. Loiselle, FFSG’s Species of the Month for June is the entire superflock of Lake Victoria’s endemic Haplochromine cichlids. These closely related small multi-coloured cichlids, generally known as Haplochromine cichlids or Fulu, provide an astounding example of adaptive radiation – morphologically, ecologically, and behaviourally. They were once the most speciose fishes in Lake Victoria with around 500 species. Unfortunately, many have yet to be described or studied by scientists, and many are now rarely seen and feared extinct. A combination of factors are believed to be the cause, including the introduction of the non-native invasive and piscivorous Nile perch, Lates niloticus, overfishing. Significant changes to the lake system from agriculture, including tea and cotton plantations, has resulted in pollutants and sediments being released into the lake. An increase in water turbidity from sediment pollution is believed to have impacted upon the reproductive success of these primarily visually orientated fishes.

Delve into the world of Lake Victoria’s Haplochromines here

Images © Jeremy Shelton

The Clanwilliam sandfish, Labeo seeberi, is South Africa’s most threatened migratory freshwater fish. Once widespread throughout the Olifants-Doring River system, today they are threatened by dams which prevent upstream migration to their spawning grounds, and predation by non-native species. There are now only two known tributaries where sandfish still spawn: the Oorlogskloof and Biedouw rivers.  To prevent the extinction of the Clanwilliam sandfish, the Freshwater Research Centre and partners launched the Saving Sandfish project in 2020. This led to the largest freshwater fish rescue on record, with teams of scientists, farmers and members of the local community all involved.  Together, they relocated fish above reservoir walls, which were cleared of non-native fish to create sandfish sanctuaries. Once juveniles have reached 15 cm they are considered ‘bass-proof’ (i.e. too large to be eaten by bass) and are released back into the wild with tiny PIT tags which allow scientists to track their movements and survival. To date nearly 3,000 bass-proof sandfish have been released, and results to date show a 16.4% return rate, and a more than doubling of the size of the Biedouw spawning population.

To find out more about this species and the work to save it please read the FFSG supported report Africa’s Forgotten Fishes and watch the Saving Sandfish films which takes you on an amazing journey into the hidden world of this Endangered fish and what is being done to help it. 

Images © Kathy Hughes

This little flattened thumb-size fish with its attractive colouring and blinking eyes is found in the mountains of central Vietnam, in fast-flowing, highly oxygenated waters where flow rates are so high that competitors would be washed away. To cope with these extreme flow rates, hillstream loaches have evolved adaptations to stick to the bottom, equivalent to the downforce generating wings and skirts of F1 racing cars, and scale architecture reminiscent of the drag-reducing riblets of mako sharks; research sees potential applications of its adaptations for engineering designs that need to be dynamically attached to surfaces in flow, e.g. tags to fish, temporary medical units in bodily vessels, and inspection devices on ships or aeroplane hulls https://doi.org/10.1101/851592 .

These little fish have also lately become popular in the aquarium trade, but need very specialised conditions; most fish will not receive these and live short unhealthy lives.  https://www.biology.ox.ac.uk/article/extreme-flow-for-hillstream-loaches

Images © Institute REVIVO

The Danube salmon or huchen (Hucho hucho) is one of the largest members of the salmonid family (Salmonidae). The Danube salmon is an endemic and flagship species of the Danube River basin. As a result of significant population declines, the species is listed as Vulnerable (VU) according to IUCN criteria (IUCN Red List, 2024).

Its charisma is not based solely on appearance or specific behavior, it primarily stems from its size and strength. Adults can grow up to 140 cm in length and weigh up to 30 kg, with a lifespan that can exceed 15 years. It is a predatory fish: adults primarily feed on other fish, while juveniles feed on aquatic invertebrates and fish larvae.

Danube salmon spawn in pairs in small tributaries, where females dig spawning pits in gravel beds to deposit their eggs. Juveniles initially remain in these smaller streams but later migrate to larger rivers. The species is territorial and inhabits large pre-Alpine and lowland rivers of the Balkan Peninsula. It is considered a medium-range migratory species.

Over 1,800 kilometers of rivers with self-sustaining populations have been identified in the Balkans, representing 65% of the species’ total distribution range. Key rivers include the Drina, Kolpa, Lim, Sava, Tara and Una.

The greatest threat to the Danube salmon is habitat loss, resulting from both river fragmentation caused by hydropower development and river regulation. In some areas, poaching remains a significant issue, as the species is highly prized in sport fishing. In the past, polluted waters also severely impacted its populations.

Despite various conservation programs, planned and ongoing hydropower projects, all over the Balkan peninsula, represent a serious threat. Some dams are already under construction, while many more are proposed. Their implementation would further isolate populations and destroy its habitat and could bring this species to extinction.

Institute REVIVO, an NGO from Slovenia, is involved in the international project Danube LifeLines, striving to improve conditions for the conservation of migratory fish species

Nominated by Žiga Tertinek, Institute REVIVO