Abstract:
Fungal diseases are prevalent in fish and have the potential of limiting productivity in
aquaculture. This study aimed to isolate and determine fungal infections in hatchery with
female Rufiji tilapia and their hybrids of male Rufiji tilapia and female Nile tilapia. An
experimental study design was conducted to determine the occurrence of fungal infections
and to characterize the isolates of Aspergillus flavus and Aspergillus niger. Fish samples
were randomly collected from the hatchery at the Institute of Marine Sciences Mariculture
centre in Pangani. In the sampled fish the gills, gastrointestinal tract and skin were
collected. The morphological and physiological tests were employed to isolate and
identify fungi using SDA. The lactophenol detached crystal cotton blue was used for
characterization of fungi. The Rufiji tilapia stocked at different salinities were infected by
A. niger and A. flavus at 72.4 % and 17.1% (n = 61) respectively. The prevalence of A.
niger and A. flavus in water of tilapia and hybrids was 37.4 % and 10.6% respectively.
Rufiji tilapia and hybrids were infected by A. niger and A. flavus at 37.9 % and 6.5 % (n =
62) respectively. For PCR based analysis, fragments of bp400 and 895 were detected for
A.flavus and bp290 for A.niger. Despite the percentage variations for fungal isolates in
some of the fish, overall, there was a significant (P0.05) reduction of prevalence of
fungal infections with increasing salinities. In the hybrids, an increase in salinity did not
influence the prevalence of Aspergillus species (P0.05). Increase in salinity has no
influence on the growth of A. flavus in fish organs of Rufiji tilapia. Conventional methods
are time-consuming and less sensitive; PCR methods provide more specification and high
sensitivity of the target organism. Different salinities of 15, 25 and 35 are potential for
mariculture since they cannot support the existence of A. niger unlike A. flavus, which
showed significant difference in fish organs.
