In the present study we compared morphological characteristics of the endemic fish species Lamprichthys tanganicanus (Poeciliidae) from Lake Tanganyika to those of similar fish samples which have appeared in Lake Kivu since 2006 to assess: (1) the taxonomic status of fish samples from Lake Kivu fisheries; (2) the food habits and fecundity of this fish and (3) the way by which this fish may have been introduced into this lake. Fish samples from Lake Kivu were collected in the bay of Bukavu and in Lake Tanganyika at Uvira. Metrics and meristics of Lamprichthys tanganicanus samples collected from Tanganyika were similar to those of fish collected in Lake Kivu indicating that recent fish samples caught together with Limnothrissa miodon in this lake indeed belong to Lamprichthys tanganicanus, a non-cichlid fish well known to be endemic to Lake Tanganyika. Genetic studies carried out on samples of this fish from both lakes support those conclusions. Moreover, mixed schools of Lamprichthys tanganicanus and Limnothrissa miodon fry were collected in the littoral zone of Lake Tanganyika suggesting that fry of the former species may have been accidentally introduced in Lake Kivu together with that of Limnothrissa miodon fifty years ago. Late appearance of this Tanganyikan non-cichlid species thirty years after Limnothissa miodon is discussed in relation to the biological characteristics of these two species.
This study was focused on the description of fishing gears on Lake Kivu. Data were collected from March 2012 to February 2014 in Goma, Bukavu, and Kibuye fishing stations. The study findings indicate that gill nets, beach seine, lift net, trammel net composed of two panels of small and larger meshes (mosquito net attached to lift net parts), mosquito net, longline, single line, pots, and cast net were identified as fishing gears used on Lake Kivu. Longline was more selective (2 species) in terms of species selection. The lift net presented the best catch (19.4 ± 11 kg), while the trammel net showed the highest CPUE (7.9 ± 6.1 kg/h). The large dimensions of gears and the long netting duration characterized gillnets (1023.2 ± 620.1 m2 ) and longline (10.3 ± 4.6 hours) respectively. Cast-nets (20mm) showed the largest mesh size, while mosquito nets (1 ± 0.3 mm) were the smallest.
Background and aims – Massive algae growth resulting in a phytoplankton bloom is a very rare event in the meromictic and oligotrophic Lake Tanganyika. Such a bloom was observed in the north of the lake in September 2018. Phytoplankton species composition during this bloom is compared to a documented bloom in 1955, and to the composition in September 2011–2013. Meteorological observations suggest hydrodynamics could explain the occurrence of the 2018 bloom.Material and methods – Phytoplankton net samples were taken in the pelagic and littoral zone near Uvira during five consecutive days of the bloom in 2018. For the period 2011–2013, quantitative phytoplankton samples were obtained during a weekly sampling at the same sites. Samples were analysed with an inverted microscope and relative abundances of the algal species were compared. Key results – Dolichospermum flosaquae (Cyanobacteria) initially dominated the bloom followed by high relative abundance of Limnococcus limneticus (Cyanobacteria) on the third sampling day in September 2018. In the pelagic zone an increase of Nitzschia asterionelloides (Bacillariophyta), and Dictyosphaerium and Lobocystis (Chlorophyta) was observed while in the littoral zone increasing abundances of dinophytes were noted. Dolichospermum flosaquae was also responsible for the bloom reported in 1955, but was only sporadically observed in the 2011–2013 samples. Although Limnococcus limneticus was present in 2011–2013, it never reached relative abundances as high as during the 2018 bloom. Meteorological data indicate that 2018 experienced different conditions compared to previous years: strong south-east winds from May to September with a more eastern direction of the wind, and a well-marked drop in atmospheric pressure between August and September.Conclusion – After a very windy season, the combination of strong hydrodynamics, calmer lake conditions, and high solar radiation and air temperature in September 2018 was favourable for a massive Cyanobacteria bloom in the north of Lake Tanganyika.
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