'Cand. Actinochlamydia clariae' gen. nov., sp. nov., a Unique Intracellular Bacterium Causing Epitheliocystis in Catfish (Clarias gariepinus) in Uganda

Background and Objectives: Epitheliocystis, caused by bacteria infecting gill epithelial cells in fish, is common among a large range of fish species in both fresh-and seawater. The aquaculture industry considers epitheliocystis an important problem. It affects the welfare of the fish and the resulting gill disease may lead to mortalities. In a culture facility in Kampala, Uganda, juveniles of the African sharptooth catfish (Clarias gariepinus) was observed swimming in the surface, sometimes belly up, showing signs of respiratory problems. Histological examination of gill tissues from this fish revealed large amounts of epitheliocysts, and also presence of a few Ichthyobodo sp. and Trichodina sp. Methods and Results: Sequencing of the epitheliocystis bacterium 16S rRNA gene shows 86.3% similarity with Candidatus Piscichlamydia salmonis causing epitheliocystis in Atlantic salmon (Salmo salar). Transmission electron microscopy showed that the morphology of the developmental stages of the bacterium is similar to that of members of the family Chlamydiaceae. The similarity of the bacterium rRNA gene sequences compared with other chlamydia-like bacteria ranged between 80.5% and 86.3%. Inclusions containing this new bacterium have tubules/channels (termed actinae) that are radiating from the inclusion membrane and opening on the cell surface or in neighbouring cells. Conclusions: Radiation of tubules/channels (actinae) from the inclusion membrane has never been described in any of the other members of Chlamydiales. It seems to be a completely new character and an apomorphy. We propose the name Candidatus Actinochlamydia clariae gen. nov., sp. nov. (Actinochlamydiaceae fam. nov., order Chlamydiales, phylum Chlamydiae) for this new agent causing epitheliocystis in African sharptooth catfish

Dietary inclusion of pine pollen alters sex ratio and promotes growth of Nile tilapia (Oreochromis niloticus, L. 1758)

The potential of pine pollen (PP) to masculinize sexually undifferentiated Nile tilapia was evaluated by feeding graded levels of PP (0.08–3.20 g kg-1 basal diet) to triplicate groups of three-day-old Nile tilapia for 28 days. Masculinization and associated differences in growth were compared to fish individuals fed the same basal diet with no PP (CT; negative control) and with 0.06 g 17α-methyltestosterone (MT) kg-1 basal diet (positive control). Both PP and MT treatments significantly skewed the expected 50:50 (male: female) ratio towards more male individuals. Notably, MT and 1.28 g PP kg-1 of diet produced a significantly high proportion of males (89.2 ± 2.2% and 80.0 ± 2.9% respectively), compared to 50.8 ± 2.2% in the CT treatment (P < 0.001). Except for 0.08 g PP kg-1 of diet, the final body weight and specific growth rate of individuals fed PP and MT-supplemented feeds were significantly higher than fish from the CT group. Although 1.28 g PP kg-1 diet produced the highest masculinization, the fish fed 3.20 g PP kg-1 diet had the highest final weight (14.73 ± 0.54 g), suggesting the presence of growth enhancers in PP. Similarly, a superior feed conversion ratio was recorded in both PP and MT-treated groups compared to the CT treatment (P = 0.024). However, the condition factor and survival rate of fish in all groups did not differ significantly. Overall, 1.28 g PP kg-1 diet was potent in sex inversion and promoted the growth of Nile tilapia, making PP a promising alternative to MT in the production of all-male stock

Effectiveness of Surfaces used for Sun-drying Rastrineobola argentea along Lake Victoria shoreline, Uganda

Mukene (Rastrineobola argentea) makes up 60% of the total fish catch in Lake Victoria and it is preserved by open sun-drying on various surfaces. This study evaluated drying time and the quality of mukene dried on bare-ground, concrete, net-on-grass, shade-net rack and wire-mesh rack. The drying time on all surfaces ranged from 7 hours on shade-net to 8hours on wire-mesh except on the net-on-grass which took 9.4 hours. The total bacterial load ranged from 1.0 x 105cfu g-1to 2.3 x 108cfu g-1 while total volatile base nitrogen (TVB-N) varied from 17.2 mgN100g-1 to 23.8 mgN100g-1 in fish dried on shade-net and bare-ground respectively. It was concluded that the type of surface significantly affected drying time, contamination by bacteria, animal and plant detritus and pebbles, as well as concentration of total volatile base nitrates (TVB-N) in mukene during drying.Keywords: Contamination, Faecal coliforms, Peroxide value, Spoilage, Sun-drying, Total bacterial load, Total volatile base nitrates

Molecular genetic diversity and differentiation of Nile tilapia (Oreochromis niloticus, L. 1758) in East African natural and stocked populations

Abstract Background The need for enhancing the productivity of fisheries in Africa triggered the introduction of non-native fish, causing dramatic changes to local species. In East Africa, the extensive translocation of Nile tilapia (Oreochromis niloticus) is one of the major factors in this respect. Using 40 microsatellite loci with SSR-GBS techniques, we amplified a total of 664 individuals to investigate the genetic structure of O. niloticus from East Africa in comparison to Ethiopian and Burkina Faso populations. Results All three African regions were characterized by independent gene-pools, however, the Ethiopian population from Lake Tana was genetically more divergent (Fst = 2.1) than expected suggesting that it might be a different sub-species. In East Africa, the genetic structure was congruent with both geographical location and anthropogenic activities (Isolation By Distance for East Africa, R2 = 0.67 and Uganda, R2 = 0.24). O. niloticus from Lake Turkana (Kenya) was isolated, while in Uganda, despite populations being rather similar to each other, two main natural catchments were able to be defined. We show that these two groups contributed to the gene-pool of different non-native populations. Moreover, admixture and possible hybridization with other tilapiine species may have contributed to the genetic divergence found in some populations such as Lake Victoria. We detected other factors that might be affecting Nile tilapia genetic variation. For example, most of the populations have gone through a reduction in genetic diversity, which can be a consequence of bottleneck (G-W, < 0.5) caused by overfishing, genetic erosion due to fragmentation or founder effect resulting from stocking activities. Conclusions The anthropogenic activities particularly in the East African O. niloticus translocations, promoted artificial admixture among Nile Tilapia populations. Translocations may also have triggered hybridization with the native congenerics, which needs to be further studied. These events may contribute to outbreeding depression and hence compromising the sustainability of the species in the region

Growth and Nutrient Removal Efficiency of Sweet Wormwood (<i>Artemisia annua</i>) in a Recirculating Aquaculture System for Nile Tilapia (<i>Oreochromis niloticus</i>)

The maintenance of optimal water quality for fish production is one of the major challenges in aquaculture. Aquaponic systems can improve the quality of water for fish by removing the undesirable wastes and in turn produce a second marketable crop. However, there is no information on the growth and nutrient removal capability of Artemisia annua in aquaponic systems. This study evaluated the effect of plant density on water quality, the growth of A. annua and Oreochromis niloticus in a small scale aquaponic system in Kenya. The aquaponic system consisted of three treatments representing different plant densities (D1: 48 plants/m2, D2: 24 plants/m2 and D3:0 plants/m2). The high plant density system contributed significantly (p &lt; 0.05) to the removal of all nutrients. The removal efficiency of ammonia was significantly higher in D1 (64.1 &#177; 14.7%) than in D2 (44.5 &#177; 6.8%) and D3 (38.0 &#177; 12.1%). Nitrates and nitrites were inconsistent, whereas phosphorus increased gradually in all treatments. The productivity of plants was higher in D1 than D2. Fish growth rates were significantly higher in D1 (0.35 &#177; 0.03 g/d) and D2 (0.32 &#177; 0.02 g/d) than in D3 (0.22 &#177; 0.04 g/d). The results show that A. annua can be cultivated in aquaponic systems due to its nitrogen removal capabilities

Effects of aerated and non-aerated biofilters on effluent water treatment from a small-scale recirculating aquaculture system for Nile tilapia (Oreochromis niloticus L.)

Most recirculation aquaculture systems (RAS) use aerated biofilters to maintain suitable water quality for fish production. However, application of non-aerated biofilters may provide opportunities to lower aeration costs, water usage and concentration of all nitrogenous wastes in the effluent water. Our study aimed at comparing the biofiltration performance characteristics of two biofilters: a conventional aerated biofilter and a non-aerated biofilter receiving the same effluent water from a small-scale RAS. The two biofilters were evaluated in triplicate and tested concurrently for seven months. Water quality parameters were monitored at the biofilter inlets and outlets and in the fish tanks. At the beginning of the experiment, the concentration of ammonia at the two biofilter outlets were not significantly different. However, the concentrations decreased with time reaching mean values of 1.33 ± 0.02 mg L−1 and 1.23 ± 0.21 mg L−1 N-NH4 in the aerated and non-aerated biofilters, respectively. Whereas phosphorus and nitrate levels were significantly high in the aerated biofilter. There was no significant difference in the growth of fish between the aerated and non-aerated biofilters. The results suggest that non-aerated biofilters can be as effective as aerated biofilters in maintaining suitable water quality for O. niloticus production

Paraffin sections from gill tissues.

<p>The sections of gill tissue from <i>Clarias gariepinus</i> have been processed for <i>in situ</i> hybridization or stained with HES. A) Primary filament showing dark-blue stained <i>Candidatus</i> Actinochlamydia clariae inclusions, stained with antisense DIG-labelled RNA-probe against <i>Ca.</i> A. clariae 16S rRNA. Cells with inclusions are particularly frequent at the filament tip. Bar = 100.0 µm. B) Same primary filament stained with a sense probe, demonstrating absence of staining in the inclusions (examples indicated by arrows). Bar = 100.0 µm. C) HES stained section of the same filament tip. Bar = 100.0 µm. D) Magnification of an IHC stained inclusion, where the actiniae are discernible (arrowhead). Bar 10.0 = µm.</p

Semi-thin sections of infected primary lamellas from African sharptooth catfish.

<p>Pictures of semi-thin sections of the primary gill lamellas from African sharptooth catfish infected with <i>Candidatus</i> Actinochlamydia clariae. Arrows point to cysts of variable sizes. The majority of the cysts are located towards the apical part of the primary lamellas. A) Bar = 60.0 µm. B) Bar = 30.0 µm.</p

Section through inclusion with IBs.

<p>Sections through inclusions containing mainly IBs. The IBs have condensed nucleoids, but the rest of the content of the bacteria is not condensed. A) Bar = 5.0 µm. B) Bar = 0.5 µm. C) Bar = 0.5 µm.</p