Multiple repeated patterns of adaptive radiation were revealed in cyprinid fish inhabiting the compact geographic region of the ethiopian Highlands. We found four independently evolved radiations in the evolutionary hexaploid (2n = 150) Labeobarbus lineage based on matrilineal relationships of >800 individuals. Each radiation displayed similar patterns of mouth phenotype diversification, and included ecomorphs/species of the generalized, lipped, scraping (one or two), and large-mouthed (one to three) types. All radiations were detected in geographically isolated rivers, and originated from different ancestral populations. This is the first documented case in which numerous parallel radiations of fishes occurred-via different ways-in a riverine environment. Some radiations are very recent and monophyletic, while others are older and include ecomorphs that originated in separate mini flocks and later combined into one. The diversification bursts among Ethiopian Labeobarbus were detected in the mid-upper reaches of rivers (1050-1550 m above sea level), which likely offer ecological opportunities that include diverse habitats yet poor fauna (i.e. lower competition and relaxed selection). this promising example of parallel evolution of adaptive radiation warrants further investigation.In the pioneering work on South African cichlids and catfishes, Joyce et al. 21 and Day et al. 19 suggested that the riverine flocks are remnants of radiations that emerged in a paleolake. This suggestion is corroborated by the finding of the Lake Tanganyika endemics beyond the lake basin 33 . While some riverine radiations clearly have lacustrine origins, it is likely that other riverine radiations originate from sources other than lakes. Hence, we aimed to test whether the same environmental factors that trigger lacustrine radiation can also act in rivers.In general, the main prerequisites for adaptive radiation are: (1) environmental stability for evolutionarily significant periods (starting from thousands of years ago); and (2) physical isolation from the river drainages harboring diverse fish faunas 15,20,31 . The latter serves a dual purpose: first, it provides the ecological opportunities for niche divergence at the initial stages of radiation, and later it prevents the extinction of diverged forms caused by competition with highly specialized species from other systematic groups. These processes can operate in specific and rather rare parts of the riverine network. For example, the segment of the Genale River that harbours the radiating assemblage of distinct forms of the Labeobarbus is situated in the apparently old canyon, isolated by the Baratieri Falls from the lower reaches of the river system and characterized by the depauperate fish fauna 20 .If the fish radiations in rivers are similar to the evolutionary phenomena experienced in lakes, they should display similar evolutionary patterns. It is well known that adaptive radiations are often repeatable in different organisms as exemplified from spiders 34 , fish 35 , and liz...

Fish are recognized as the main source of physiologically important omega-3 long-chain polyunsaturated fatty acids, namely, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), for human nutrition. However, muscle tissue contents of these fatty acids in diverse fish species, i.e., their nutritive value for humans, varied within two orders of magnitude. We reviewed contents of EPA and DHA, measured by similar methods using an internal standard during chromatography as mg per g of wet mass in 172 fish species belonging to 16 orders, to evaluate probable variations in phylogenetic and ecological drivers. EPA+DHA content varied from 25.6 mg•g-1 of wet mass (Sardinops sagax) to 0.12 mg•g-1 (Gymnura spp.). Multidimensional redundancy analysis revealed that among phylogenetic, ecomorphological and abiotic environmental factors, the highest proportion of variation contribution belonged to the shared contribution of sets of phylogenetic and ecomorphological factors. Specifically, the highest values of EPA+DHA content were characteristic of fish belonging to the orders Clupeiformes or Salmoniformes, were pelagic fast swimmers, ate zooplankton and inhabited marine waters or migrated from fresh to marine waters (anadromous migrations). High EPA and DHA content in muscle tissues of the above species appeared to be a metabolic adaptation for fast continuous swimming. In contrast to common beliefs, our meta-analysis did not support the significant influence of higher trophic levels (piscivory) and cold environments (homeoviscous adaptation) on EPA and DHA content in fish. However, many causes of high and low levels of physiologically important fatty acids in certain fish species remained unexplained and require evaluation in future studies.

In several Russian northern lakes and rivers, Arctic cisco Coregonus autumnalis, least cisco C. sardinella, peled C. peled, tugun C. tugun, broad whitefish C. nasus, whitefish C. lavaretus and vendace C. albula were sampled in periods of officially permitted commercial fishery. Special attention was paid to contents (mg g of wet weight) of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in muscle tissues (filets), which are essential for human nutrition. The highest values of EPA + DHA content in semi-anadromous fish and freshwater fish were recorded for C. autumnalis from the Yenisei River, 17.60 mg g wet weight, and for C. lavaretus from the Sobachye Lake, 16.61 mg g wet weight, respectively. Intra-genus variations of EPA + DHA contents of Coregonus species were from 1.87 to 17.60 mg g wet weight. Since the congeneric species were genetically close to each other, the variations in EPA and DHA contents were thought to be caused primarily by ecological factors: migrational capability, type of feeding and trophic status of aquatic ecosystems. In general, the majority of studied species appeared to be of a high nutritive value for humans, although unfavorable environmental conditions could considerably diminish this value.

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