Isichthys henryi
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Isichthys henryi |
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| Isichthys henryi | ||||||||||||
| Gill, 1863 |
Isichthys henryi is an African freshwater fish from the Nilhechte family(Mormyridae). It occurs in two separate areas of distribution in West Africa. One includes rivers near the coast in Guinea , Sierra Leone and Liberia , the other lies in the Niger river basin and extends via Cameroon and Gabon to the Kouilou in the Republic of the Congo .
features
Isichthys henryi becomes a maximum of 28.7 cm long and has an eel-like elongated, laterally slightly flattened body. The trunk is monochrome in the color of dark chocolate , the head is yellow-brown, the fin rays are dark brown, the fin membrane is transparent. The body height corresponds to 5.9 to 11.9% of the standard length , the body width 70% of the body height. The dorsal and anal fin are long, the dorsal fin, which reaches 44 to 48% of the standard length, begins well in front of the anal fin. It is supported by 42 to 49 fin rays in the population from Niger and Lower Guinea, and 37 to 44 fin rays in the population from Upper Guinea. The anal fin reaches 39 to 41% of the standard length and has 40 to 48 or 36 to 44 fin rays. Isichthys henryi can be distinguished from the elongated Brienomyrus species - and some elongated Mormyrops species - by the long dorsal fin; in Brienomyrus and Mormyrops the anal fin is always the longest.
In Isichthys henryi, the pelvic fins are closer to the anal fin than to the pectoral fins. The tail fin stalk is short and only reaches 8% of the standard length. It is 1.7 to 3.3 times longer than it is high and is surrounded by 16 to 20 scales, which are sometimes irregular, making it difficult to determine the number of scales. Along the sidelines , the population from Niger and Lower Guinea has 120 to 130 scales, while the population from Upper Guinea has 135 to 145 scales.
The head is 1.75 to 2 times as long as it is high. The "snout" (region in front of the eyes) makes up 21 to 25% of the head length and ends in a rounded "bulbous organ". The mouth is below and has five to six teeth in the upper jaw and six two-pointed teeth in the lower jaw. There are electroreceptors on the outside of the lower jaw. The eyes are small, their diameter is half the length of the snout. Around the eyes there are four other large electroreceptors whose diameter corresponds to that of the nostrils.
Like all Nilhechte, Isichthys henryi is capable of electrical communication and electrical orientation. Electroreceptors are located on the head, back, and some parts of the abdomen. They are missing on the sides and on the tail fin stalk, where the electrical organ can be found. The electrical signal from Isichthys henryi is of low frequency and different between females and males.
Systematics
Isichthys henryi is the only species in the genus Isichthys . Although there are differences between the two populations in terms of fin rays and scale rows, they are considered insufficient to split the species into two species. Isichthys is the sister genus of Brienomyrus .
literature
- Melanie Stiassny, Guy Teugels & Carl D. Hopkins: The Fresh and Brackish Water Fishes of Lower Guinea, West-Central Africa, Volume 1. ISBN 9789074752206
Web links
- Isichthys henryi on Fishbase.org (English)
- Isichthys henryi Gill, 1863
- Isichthys henryi inthe IUCN Red List of Threatened Species 2013.2. Submitted by: Moelants, T. & Olaosebikan, BD, 2009. Retrieved January 12, 2014.