International Journal of Aquaculture, 2015, Vol.5, No.4 1
-
5
2
concerns about fish diseases and parasitic infestation
have existed for years yet little scientific evidence is
available on the subject. Parasitic infections of fish
can
be a major setback in achieving maximum production
per unit area of culture. As the development of
aquaculture has advanced, one essentially unsolved
problem is the prevention of economic losses to
production in concrete ponds due to poor management
practices which resulted in disease infestation as a
result of high prevalence and intensity of parasite load.
While this problem remains unsolved, such diseases
documented evidence on the prevention and control
are apparently deficient.
The study aimed at investigating the presence of fish
parasites among
Oreochromis niloticus
cultured in
concrete ponds. Pathogenic effects of parasites on
hosts manifest themselves in various ways. According
to Huitric et al. (2002) economic effects of parasites on
fishes are mass mortality, rejection of infected fish by
the market when parasites and/or lesions are visible
and more importantly, retarded growth and weight
losses of the infected fish. Furthermore, some fish
parasites are potentially pathogenic for man when the
parasitized fish are consumed not well cooked, cold
smoked, marinated or just raw (Naylor et al 2000).
There are some objectives of the Millennium
Development Goals on poverty and hunger. The
information related to parasites affecting tilapia
fingerlings in concrete ponds would be very important
for the implementation of future projects in Tamale,
Ghana. Our objective in the present work is to
investigate the prevalence and mean intensities of
ecto-parasites of Nile tilapia (
Oreochromis niloticus
).
2 Results
2.1 Physico-chemical Characteristics of pond and
Fish Examined for parasites Infestation
The dissolved oxygen (DO) ranged from 4.10 mg/L to
5.12 mg/L with a mean of 4.32 mg/L ±0.39. The pH
ranged from 5.86 to 6.57 with a mean of 6.17±0.23
and temperature ranged from 27.10
℃
to 32.49
℃
with a mean of 28.48
℃
±2.31. Nitrate was 30.00 mg/L
to 32.23 mg/L with the mean of 30.63 mg/L ±1.03.
The total number of fish examined was 240 individual
fishes for the six month study. Out of the fish sampled
for examination, 35% were adult fish while fingerlings
were 65%. Out of 240 samples examined, 35 fishes
representing (15%) of the total fish examined were
parasitized. The number of fingerlings parasitized was
slightly higher (0.8%) than the number of adult fishes
found to be infected (Table 1). The gills of the fish
were observed to have more parasites as indicated in
(Table 2). The fish size with the highest (57%)
prevalence was 11-13cm. It was followed by fishes
with sizes from 14-16 cm, which had a prevalence
level of 28%. Low infestations of ecto-parasites were
observed at the size ranges of 8 -10 cm and 17-19 cm
with prevalence level of 9% and 6% respectively. In
terms of prevalence in relation to body weight, the
body weight class with the highest prevalence was
37% each for 11-30 g and 31-50 g fish. Body weight
class of 51-70 g followed with prevalence of 11% and
9% with the lowest (6%) in weight class of 91-110 g.
Table 1 Frequency of fingerlings and adult fish infection
Parameters / size
(cm)
Fingerlings
8 -11
Adults
12 - 18
Total
№ of fish
parasitized
23 (14.8%)
12 (14.1%)
35
№ of fish
non-parasitized
132 (85.2)
73 (85.9%)
205
Total № of fish
examined
155 (100%)
85 (100%)
240
T
able 2 Parasites encountered and their distributio
n
Parasite
Location
No of fish
parasitized
No of parasites
load
Trichodina
spp.
Gills
8
16
Ichthyophthirius
multifilis
Skin
Surface
& Gills
21
31
Monogeneans
Gills
6
9
Total
35
56
During the six month study, two protozoan and
metazoan ecto-parasites namely
Trichodina
spp.
(Ciliate),
monogeneans
and
Ichthyophthirius multifilis
(Ciliate) were found on the gills and the skin mucus of
O. niloticus.
Out of 240 fish that were examined, 21
were parasitized with
Ichthyophthirius multifilis
, 8
were found to be infected with
Trichodina
spp. and 6
were infected with Monogeneans.The peak of
infestation was observed to be high in the dry season
