Population morphological variation of the Nile perch (Lates niloticus, L. 1758), of East African Lakes and their associated waters

In this study an attempt was made to determine whether there are morphological variations associated with the different geographical populations of the Nile perch of East Africa. Analyses of the levels of morphological differentiation based on morphological characterisation and variation were carried out. The study was based on 864 Nile perch sampled from 25 different locations from different Lakes in the region and 10 morphological characters. Also determined were the length – weight relationships and condition factor of sampled Nile perch. The log transformed data of all sampled Nile perch were subjected to multivariate analysis, using ‘PAST’ statistical software. Findings showed that peduncle form and size, of all the variables used in this study, contributed most to the variance. The analysis clustered the Nile perch into two groups, which were found to be as characterised by earlier morphological description of this species and most probably are representatives of two distinct taxa of Nile perch in the East African waters. The LWRs and condition factor conformed to the fish isometric growth formula W = aLb with the value for the pooled data being W = 0.6664L0.3264. The existence of 2 morphs agrees with earlier taxonomists (Harrison, 1991; Ribbink, 1987; Bwathondi, 1985; Holden, 1967) who proposed that Nile perch exists in two populations – a bigger shallow water dwelling morph and a smaller deep open water dwelling morph. This calls for identification and mapping of the 2 populations in the different waters of East Africa that may require application of different management regimes.Keywords: Nile perch, taxa, morphological variation, East Africa

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

From the 1950s onwards, programmes to promote aquaculture and improve capture fisheries in East Africa have relied heavily on the promise held by introduced species. In Tanzania these introductions have been poorly documented. Here we report the findings of surveys of inland water bodies across Tanzania between 2011 and 2017 that clarify distributions of tilapiine cichlids of the genus Oreochromis. We identified Oreochromis from 123 sampling locations, including 14 taxa restricted to their native range and three species that have established populations beyond their native range. Of these three species, the only exotic species found was blue-spotted tilapia (Oreochromis leucostictus), while Nile tilapia (Oreochromis niloticus) and Singida tilapia (Oreochromis esculentus), which are both naturally found within the country of Tanzania, have been translocated beyond their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, 2070) East African climate. These models indicated that presence of suitable habitat for these introduced species will persist and potentially expand across the region. The clarification of distributions provided here can help inform the monitoring and management of biodiversity, and inform policy related to the future role of introduced species in fisheries and aquaculture

Preliminary results of the analysis of the population structure of the Nile perch (Lates niloticus linnaeus, 1758) of Lake Victoria using microsatellite markers

Preliminary results are provided of a study instituted to analyze the genetic population structure of the Nile perch in Lake Victoria since 2002. 293 individuals from six geographically distinct locations withinthe lake were analyzed using two polymorphic microsatellite DNA markers. Tests for differentiation with an overall FST = 0.03 (P < 0.05) suggested that populations were genetically differentiated, with thecloset population pairs Nyaburu-Rubafu and Mirunda-Maboko as the most differentiated populations. There was an extensive gene flow between the populations (Nm = 20.77). The overall gene diversity(0.17) was low. All the results point to the fact that Nile perch was only recently introduced species in the lake based on a small founder population, which though slow in establishing later exploded tobecome the most dominant species in the lake. On the whole the two loci indicate some level of differentiation between locations; however, the levels of genetic differentiation shown by the two lociwere not enough to define the structure of Nile perch stocks, and assess the level of exchange between locations. Further work is underway using bigger number of microsatellite markers

Characterisation of fish oils of mukene (Rastrineobola argentae) of Nile basin waters – Lake Victoria, Lake Kyoga and the Victoria Nile River.

Mukene (Rastrineobola argentea) is a freshwater tiny cyprinid endemic to Lake Victoria, Lake Kyoga and the Victoria Nile River. It is the third most important commercial fishery of Uganda after Lates niloticus and Oreochromis niloticus. The study investigated the fatty acid content of the fishmeal of whole fish of R. argentea and for differences in the fatty acid profile of the samples from the different water bodies. Fatty acid composition of fishmeal obtained from samples collected from the two lakes and the Victoria Nile River was determined using chemometric method for five fish samples from each location and subjected to multivariate analysis. In each fish the fatty acids detected ranged from 14 to 24 carbons. Palmitic (16:00), stearic (18:00), oleic (18:1n9), arachidonic (20:4n6) and docosahexaenoic (22:6n3) were the principal fatty acids in all sampled fish. The fatty acid composition showed that R. argentea contain essential unsaturated fatty acids, Eicosapentanoic acid (EPA) and Docosahexaenoic acid (DHA). A 2-way ANOVA showed that there were no significant differences at 95% level between the three samples from the three connected water bodies, therefore fatty acid profiles are probably not suitable for use as a chemotaxonomic tool for differentiating mukene stocks. This probably due to lack of physical barriers between the three connected water bodies, that allows for unlimited genetic exchange among the populations of R. argentea in the three water bodies.Keywords: Mukene, fatty acids profiles, Nile basin waters, chemotaxonom

A profile of the introduced Oreochromis niloticus (Pisces: Teleostei) populations in Lake Victoria Region in relation to its putative origin of Lakes Edward and Albert (Uganda - E. Africa) based on random amplified polymorphic DNA analysis

Random amplified polymorphic DNA (RAPD) marker analyses were used to profile the ‘ecological explosion’ of the introduced Oreochromis niloticus in the basins of Lakes Victoria and Kyoga in comparison to its putative origin of Lakes Edward, George and Albert. O. niloticus is currently the dominant tilapiine in Lakes Victoria and Kyoga basins following its introductions from the Lakes Albert and Edward starting in the 1920s. The populations from the Lake Victoria basin were more similar to the putative source population of Lake Edward, while the populations from Lake Kyoga were more similar to the Lake Albert population. Lake Kyoga basin populations were less diverse than those of Lake Victoria basin, consistent with the hypothesis that introductions into Kyoga were more recent and/or that a more diverse set of introductions contributed to those of Victoria basin. Wider differencesbetween Lake George and Lake Edward populations relative to distant populations was attributed to the direct transplant of Albert strain into George by a fish processing establishment in the 1970s. RAPDsoffered a quick and inexpensive molecular tool to discern fish populations that could be adopted for management of the fisheries given the recent volatile species/populations changes and/or losses inLake Victoria Region