International Journal of Aquaculture, 2015, Vol.5, No.4 1
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3
in February with a decline in the wet season in the
month of April (Figure 1).
Figure 1 The number of parasites recovered from the concrete
ponds of Water Research institute Tamale (Nov, 2013- April,
2014)
2.2 The prevalence of parasites
The prevalence of
Trichodina
sp. found on gill peaked
at 22%.
Monogeneans
also recovered from the gills
peaked at 17% and
Ichthyophthirius multifilis
recovered from the skin surface peaked
at 60%
(Figure 2).
Figure 2 The prevalence of
Trichodina
,
Monogeneans
and
Ichthyophthirius
parasites from concrete ponds at Water
Research Institute, Tamale (Nov, 2013- April, 2014)
2.3 The mean intensity of the parasites
Ichthyophthirius
had the highest mean intensity in
November and December 2013, and March 2014
whilst
Trichodina
spp. had the highest mean intensity
in January, February and April 2014. The highest
mean intensity of 2.5 was observed among the
Trichodina
spp.in January 2014. The mean intensity of
parasites ranged from 0-2.5.The details of the monthly
mean intensity of the three parasites are indicated in
(Table 3).
Table 3 The monthly mean intensity of the three identified
parasites
Trichodina sp., Monogeneans
and
Ichthyophthirius
Month
Trichodina
spp
.
Monogeneans
Ichthyophthirius
Nov-2013 0
1.0
1.7
Dec-2013 0
0
2.0
Jan-2014
2.5
0
1.5
Feb-2014 2.0
1.7
1.6
Mar-2014 0
2.0
3.0
Apr-2014 0.7
0
0
3 Discussion
The external parasites, viz., ecto-parasites:
Trichodina
sp
, Ichthyophthirius multifilis and Monogeneans were
found in relatively low occurrence during the study
period as water quality was moderately good except
for slightly acidic nature of the pond water. Fish filter
ability may be affected by water acidity, evidence in
gill susceptibility to ecto-parasite.
O. niloticus
from
the study area exhibited low prevalence and intensities
of the external parasites. The prevalence and intensity
of parasites recorded indicated that there was less
parasite occurrence on the
O. niloticus
being cultured
due to proper management practices. The few
occurrence of these ecto-parasites is likely as a result
of accidental consequences. The external parasites
could be as a result of infected hatcheries during fry
production using hapa-in-concrete pond systems. Poor
hatchery conditions provide excellent breeding
environments for ecto-parasites as intra population
transmission rates becomes high in such facilities
(Kearn 2004; Wiegertjes and Flik 2004). External
parasites from previous stocks which colonized a pond
may also be transmitted easily to new stocks which
can contribute to an increase in the infestation of
parasites when pond water are neither drained when
required nor dehydrated out. This may be a common
problem for the Institute when there is insufficient
water to be used for filling ponds.
In addition, fingerlings have under-developed immune
systems, which deliver the natural repellent ability of
the gill, fin and skin surface non-functional; and
results in increased susceptibility to ecto-parasites
which in many cases serve as mechanical vectors to
viral and bacterial infections. When such fingerlings
are used in stocking any recently established or
already existing pond, the parasites may be
