One hundred and twenty (120) fingerlings of Clarias gariepinus (mean weight: 0.96 ± 0.1g) were randomly exposed to 4 experimental treatments of petroleum, based on LC₅₀ values (6.4mg/L of crude oil, 8.7mg/L of petrol, 8.0mg/L of kerosene and 7.8mg/L of diesel oil) and replicated thrice, to determine polycyclic aromatic hydrocarbons (PAH) in exposed fish for 96 h. There was no significant difference (P > 0.05) in total (PAHs) between crude oil (97.1 ng/uL) and diesel (97.2 ng/uL) exposed fish and also between petrol (53.2 ng/uL) and kerosene (49.6 ng/uL) exposed fish, but there was a significant difference (P < 0.05) in PAH levels of the crude oil/diesel exposed -groups of fish compared to petrol/kerosene exposed -groups of fish (97.1/97.2 and 53.2/49.6 ng/uL). Naphthalene correlated positively to benzo a anthracene (r=0.672, (P < 0.05), benzo b fluoranthene (r=0.681, P < 0.05) and chrysene (r=0.615, P < 0.05) but did not correlate to fluorene. Benzo a anthracene correlated positively to benzo a pyrene (r=0.578, P < 0.05), phenathrene (r=0.685, P < 0.05) but did not correlate to acenaphthene. Fluorene correlated positively to benzo a pyrene (r=0.695, P < 0.05) but did not correlate to chrysene. Chrysene correlated positively to dibenzo a,h, pyrene (r=0.658, P < 0.05) to phenathrene and benzo b fluoranthene (r=0.659, P< 0.05). Indeno 123 cd- pyrene and fluranthene however did not correlate to other PAHs except naphthanene, acenaphthene and acenaphthylene. The level of PAH in fish may translate to the toxicity effect since crude oil and diesel with lower LC₅₀ (6.4 and 7.8 mg/L) deposited greater PAH than kerosene and petrol with higher LC₅₀ (8.7 and 8.0 mg/L) in fingerlings of C. gariepinus. High risk to cancer disorders may occur in exposed fish to petroleum with high incidence of fluorene , anthracene, pyrene and benz a anthracene which correlated positively to benzo a pyrene which provide some basis for predicting impact of oil spills on fingerling population.

The lack of quality formulated feeds as supplements or replacements for live feeds has negatively impacted the growth performance and survival rates in the larvae of many fish species, notably African catfish (C. gariepinus). Successful larval rearing relies on the availability of suitable diets that are readily consumed, easily digested, and provide the essential nutrients necessary for optimal growth and health of the fish. This study evaluated the growth performance and survival rates of C. gariepinus larvae when fed locally formulated diets. The experiment was conducted using 12 basins, each with a capacity of 20 liters. Each basin was stocked with 60 larvae in four replicates, averaging 0.03 g in weight. The experimental diets were formulated to contain three different levels of crude protein: 40%, 45%, and 50%. The larvae were fed these diets at a rate of 10-20% of their body weight over 70 days. Initially, the larvae were fed artemia at the onset of feeding in hatchling basins immediately after yolk sac absorption for the first seven days. This was followed by a blend of artemia and formulated feeds for 14 days. After 28 days, the larvae were transitioned to be exclusively fed the formulated dry feeds. The results indicated that the larvae fed on diets containing 45% and 50% crude protein exhibited significantly better overall growth performance compared to those fed on a 40% crude protein diet. Specifically, the larvae that received the 45% and 50% crude protein diets showed higher final mean weight, increased daily weight gain, and improved survival rates, which ranged from 80% to 81.5%. Notably, there was no significant difference in growth performance and survival rates between the larvae fed on 45% and 50% crude protein diets, suggesting that a 45% crude protein-formulated diet is sufficient to achieve the best growth performance and survival rates for C. gariepinus larvae. This study supports the recommendation of feeding C. gariepinus larvae with a dry diet containing 45% crude protein starting from 14 days post-hatching to enhance their growth and survival rates. However, further research is recommended to explore the effects of this feeding regimen across different agroecological zones and aquaculture systems to validate and potentially refine these findings.

: The ichthyofauna of Lake Tanganyika consists of 12 families of fish of which five belong to Siluriformes (catfishes). Studies on siluriforms and their parasites in this lake are very fragmentary. The present study was carried out to help fill the knowledge gap on the monogeneans parasitizing the siluriform fishes of Lake Tanganyika in general and more particularly Clarias gariepinus. The gills of a specimen of Clarias gariepinus (Clariidae) were examined for ectoparasites. We identified the monogenean Gyrodactylus transvaalensis (Gyrodactylidae). This is the first time this parasite was found infecting gills. We are the first to observe a large spine in the male copulatory organ of this species, and to provide measurements of its genital spines; this completes the description of the male copulatory organ which is important in standard monogenean identification. This is the first monogenean species reported on C. gariepinus at Lake Tanganyika and the third known species on a representative of Siluriformes of this lake. It brings the total number of species of Gyrodactylus recorded in Lake Tanganyika to four. Knowing that other locations where this species has been reported are geographically remote from Lake Tanganyika, we propose a “failure to diverge” phenomenon for G. transvaalensis.

Background: Aquaponics are food production systems advocated for food security and health. Their sustainability from a nutritional and plant health perspective is, however, a significant challenge. Recirculated aquaculture systems (RAS) form a major part of aquaponic systems, but knowledge about their potential to benefit plant growth and plant health is limited. The current study tested if the diversity and function of microbial communities in two commercial RAS were specific to the fish species used (Tilapia or Clarias) and sampling site (fish tanks and wastewaters), and whether they confer benefits to plants and have invitro antagonistic potential towards plant pathogens. Results: Microbial diversity and composition was found to be dependent on fish species and sample site. The Tilapia RAS hosted higher bacterial diversity than the Clarias RAS; but the latter hosted higher fungal diversity. Both Tilapia and Clarias RAS hosted bacterial and fungal communities that promoted plant growth, inhibited plant pathogens and encouraged biodegradation. The production of extracellular enzymes, related to nutrient availability and pathogen control, by bacterial strains isolated from the Tilapia and Clarias systems, makes them a promising tool in aquaponics and in their system design. Conclusions: This study explored the microbial potential of the commercial RAS with either Tilapia or Clarias as a tool to benefit the aquaponic system with respect to plant growth promotion and control of plant diseases.