International Journal of Aquaculture, 2018, Vol.8, No.5, 29-37
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3 Discussion
The study indicated that seasonal variations had an effect on parasitism. Although the sample size was limited, the
total number of parasites, prevalence rate and mean intensity varied across the three seasons of the study. The
results observed in the study indicated that the cold season registered the lowest number of parasites while the dry
season registered the highest number of parasites. The observations agreed with the findings of Ali et al. (2010)
and Ahmad and Ahmad (2013). They reported similar results of higher prevalence rate in summer and lowest in
winter. Ahmad and Ahmad (2013) reported highest infection levels in summer months and least infection levels in
winter months for helminths parasites in
Schizothorax
species (
S. plagiostomus
,
S. labiatus
,
S. ecosinus
,
S.
curvifrons
) in Shallabugh Wetland. Khurshid and Ahmad (2012) also observed higher prevalence rate of fish
parasites in summer and least in winter in some species of
Schizothorax
from River Sindh in their study. Koyun
(2012) supported the trend that some species of helminths parasites had highest prevalence during different
seasons of the year. Fish are hosts to different parasites whose diversity, strategy and abundance depends on
several factors including seasonality (Violente-Gonzalez et al. 2008; Neves et al. 2013) while parasites also
respond to the seasonal changes of the environment (Yufa and Tingbao, 2011). In contrast, Khanum et al. (2011)
reported that parasites were more abundant during the rainy season and lowest during the winter season. Sinare et
al. (2016), observed a higher prevalence rate in rainy season as compared to the dry season. According to Poulin
(2004) biotic factors such as body size of the host, population density, social behaviours, lifespan, biogeography
and diet, and abiotic factors such as temperature, size and geographical range are responsible for the changes in
the prevalence and mean intensity of the parasites. Iyaji et al. (2009) observed that as much as the chemical and
the physical factors affect the cycles of the organisms, the biotic factors were the ones that mainly affected the
prevalence and the abundance of the parasites. According to Khanum et al. (2011), the lower rate of parasite
infection during the cold season could be due to reduced feeding tendency of the host fish. On the other hand, Ali
et al. (2010) observed that during summer and autumn, the higher incidence could be due to the rise in the
temperature that resulted in favouring the development of the larvae in the secondary host. This suggests that the
seasonal fluctuations of the parasites may be due to temperature changes, availability of the intermediate host and
the host feeding behaviours. In the winter, the low prevalence rates were due to low availability consumption of
the intermediate hosts (Ali et al., 2010). Additionally, Dash (2015) highlighted that most parasites had seasonal
cycles that were definite and were influenced by the seasonal changes that affected the environment and the
physiology of the host fish. Observations by Ibiwoye et al. (2004) revealed that during the dry season evaporation
led to reduced water volume, which in turn, resulted in the contraction of the habitat thereby increasing the
densities of the host and the parasites. Consequently it resulted in more contact between the host and the parasite.
Therefore this could result in the higher infection during the dry season. The increase of the parasites during the
rainy season was attributed to rainfall, flood and reduced immunity of the hosts and prevalence of the insects that
had an impact on the water bodies (Nhiwatiwa et al., 2009; Khanum et al., 2011). Similarly, the exchange of
materials between the terrestrial and the aquatic ecosystems affect the quantities of substances and physical
chemical aspects of the water bodies (Affonso et al., 2011). Sumuduni et al. (2015) suggested that slow moving
fish were more susceptible to parasites than the fast moving fish while Munoz and Cribb (2005) reported that
larger hosts had higher parasites load than the smaller hosts. Therefore by taking in more food and having more
space, chances of infection were also high.
Koiri and Roy (2016) reported significant differences in the helminths (cestodes, nematodes and trematodes) loads
during different seasons of their study. They observed the highest number of cestodes, followed by nematodes and
lastly the trematodes. Bhure et al (2016) also observed highest number in cestodes in
Channa punctatus
species.
On the contrary, Khurshid and Ahmad (2012) recorded the highest number of trematodes followed by cestodes
with no nematodes. This suggests that different attributes could favour different parasite species proliferation.
Maguza-Tembo and Mfitilodze (2008) observed the highest number of cestodes in the buccal cavity and coelomic
cavity of
Clarias gariepinus
than in the other species of fish under study. This suggests that some species of fish
could be vulnerable to some specific species of parasites. Dash et al. (2015) suggest that this could be due to host
specificity nature of the species of parasites while Koiri and Roy (2017) maintain that seasons interfere with the
physiology and ecology of the fish and in turn it has influence over the rate of parasitic infections.
