Impact of Climate on Parasite Infestation in Wallago Attu (Bloch-Schneider, 1801) and Rita Rita (Hamilton-Buchanan,1822) Volume 59- Issue 4

Shahela Alam¹, Hamida Khanum²* and Nusrat Jahan²

• ¹Dhaka Commerce College, Bangladesh
• ²Parasitology Branch, Department of Zoology, University of Dhaka, Bangladesh

Received: November 09, 2024; Published: December 04, 2024

*Corresponding author: Hamida Khanum, Parasitology Branch, Department of Zoology, University of Dhaka, Dhaka -1000, Bangladesh

DOI: 10.26717/BJSTR.2024.59.009350

Abstract PDF

In the present investigation, a total of 250 W. attu and 350 R. rita were examined for the investigations on parasite infestation. A total of 11 species of parasites collected and identified from W. attu, one ecto-parasite (Argulus foliaceus) and 10 endo-parasites of which three were trematodes (Isoparorchis hypselobagri, Macrolecithus gotoi, Magnacetabulum trachuri); two nematodes (Contracaecum L3 larva, Cosmoxynemoids aguirrei); one cestode (Polyoncobothrium polypteri) and four acanthocephalas (Echinorhynchus kushiroense, Pallisentis ophiocephali, Acanthocephalus aculeatus, Pallisentis umbellatus). From R. rita, a total of 9 species of parasites recovered and identified, among them, one ecto-parasite (Lernaea cyprinacea) and 8 endo-parasites of which four trematodes (Notoporus leiognathi, Saccacoelium obesum, Sterrhurus musculus, Clinostomum piscidium); one nematode (Ascaroid larva) and three acanthocephalas (Cavisoma magnum, Corynosoma alaskense, Corynosoma strumosum). The prevalence of infestation of ecto-parasite was 23.6% in W. attu (59 specimens) and mean intensity of parasite was 3.11 ± 1.47 per infested fish while in R. rita, 24.8% were infected (87 specimens) with a mean intensity of parasites was 3.34 ± 1.62. The prevalence of infestation in W. attu was observed higher during winter season while in R. rita, the prevalence of infestation was higher in rainy season. The maximum intensity of parasites of W. attu was recorded in winter and in R. rita, that was found in summer. The effects of modifying factors such as sex, season, length, climatic factors and diet of the hosts on the abundance of parasites were also studied.

About 56 freshwater fish species critically or somewhat endangered in Bangladesh. A variety of factors such as food, space, temperature, salinity, physical activity influence the growth of fish (Weatherley, et al. [1,2]) and the fish body elements may change due to these factors (Kamal, et al. [3]). There has been changed in the environmental condition in Bangladesh since 1970s. Therefore it may change the parasite fauna of R. rita due to excessive use of inorganic fertilizers and pesticides in cultivated lands, discharge of industrial effluent, inadequate waste disposal etc. which indirectly cause changes in the aqua-environment. In Bangladesh rain falls in almost all the seasons of the year. The ponds, rivers, haors, bills and other water bodies then get filled with water. The rainy season is favorable for helminth infestation. At this time parasite infects aquatic animals (fish) frequently. One of the most immediate and obvious effects of global warming is the increase in temperatures around the world (Bondarenko, et al. [4]). Climate change has both direct and indirect impacts on fish stocks that are exploited commercially (Peña-Quistial, et al. [5]). Direct effects act on physiology and behavior and alter growth, development, reproductive capacity, mortality, and distribution. Indirect effects alter the productivity, structure, and composition of the ecosystems on which fish depend for food and shelter.

Brander, et. al. [6] recorded that the effects of increasing temperature on marine and freshwater ecosystems (Arctic Council 2005). Some of the changes are expected to have positive consequences for fish production (Brander, et al. [6]), and stocks become vulnerable to levels of fishing that had previously been sustainable (Friedland, et. al. [7]). Local extinctions are occurring at the edges of current ranges, particularly in freshwater and diadromous species such as salmon and sturgeon (Reynolds, et. al. [8]). The rainfall intensity of greater than 100mm is more frequent than rainfall intensity of greater than 125 mm. Although the rainfall intensity of greater than 150mm occurs infrequently but data from Bangladesh Meteorological Department (BMD) of last five years shows that the severity of this type of rainfalls increases. The trend of predicted rainfall is found increasing at a rate of 0.014mm per year whereas the observed rainfall also shows an increasing trend of 0.0103mm per year. Bangladesh’s unique geographic location, with the Indian Ocean to the south, the Himalayas to the North and the prevailing monsoons, has made it one of the wettest countries of the world. The mean annual rainfall is about 2320mm, but there are places with a mean annual rainfall of 6000mm or more (Hossain, et al. [9]).

A long duration of heavy rainfall associated with “norwester” thunderstorms is very common in Bangladesh (Hossain, et al. [9,10]). In September 2004, 341mm rainfall occurred in 8 hours in Dhaka which led to severe urban flooding (Ahmed [2]). Serious drainage congestion took place in Dhaka city due to 333mm rainfall on 28th July, 2009 (Uddin, et al. [11,12]). It is also found that climate change has a profound impact on rainfall intensity and variability (Wasimi [13]). Global Climate Models showed that global warming will increase the intensity of extreme precipitation events (Allan, et al. [14]). Regional climate models predict a large increase in annual precipitation although the more recent PRECIS run showed that the dry season is becoming drier and water deficit is increasing due to population growth (Linarce, et al. [4,15]).

Sunlight also affects temperature, and humidity is dependent on temperature. Temperature and humidity greatly influence the lives of organisms. When living things get too hot or too cold, their bodies do not function properly. Processes such as digestion, respiration, excretion and reproduction take place at an optimum (most favorable or best) temperature range. That is why many desert creatures sleep during the extremely hot days and emerge in the cool of the night to feed and engage in courtship. Second, water vapor is the most abundant of all greenhouse gases. Water vapor, like a green lens that allows green light to pass through it but absorbs red light, is a “selective absorber”. This selective absorption causes the greenhouse effect (Williams [16]). The environmental factors including climate, season and rainfall play an important role in the development of helminth parasites. Rising concentrations of greenhouse gases in the atmosphere are causing global climate change. In the coming decades, global average temperatures will increase, rainfall patterns will change, extreme weather events will become more severe, sea levels will rise and numerous other environmental changes will occur (IPCC [12]). Climate change may directly affect fishery production along many pathways. Fish reproduction, growth and migration patterns areall affected by temperature, rainfall and hydrology (Ficke, et al. [17]).

Changes in these parameters will therefore shift patterns of species abundance and availability. Saltwater intrusion caused by rising sea levels may threaten freshwater fisheries while, at the same time, creating opportunities for catching an cultivating high-value brackish or marine species (World Fish Center [18]). Changes in precipitation will affect seasonal flooding patterns that drive inland fish production. While greater wet season flooding may boost production in some inland fisheries, drier dry seasons may threaten stocks of both wild and cultured fish. In the context of long-term and climate change scenarios, rising sea-level and water temperatures may have direct effects on the fish parasite composition within a respective habitat. Anthropogenic changes have greatly altered the fish species composition, especially of large predators at high trophic levels (Hutchings, et al. [19,20]). This has measurable effects even on life history traits, substantially changing age and size at maturation (Sharpe, et al. [21]). Consequently, fish parasite numbers that are related to their changing host numbers may also change with a shift in environmental conditions. A conclusive description of the circumstances under which parasites can be used as indicators of environmental impact, however, still remains difficult (Vidal-Martınez, et. al. [22]).

The aquatic environment can be studied either directly by a regular monitoring of water quality parameters or indirectly by using bioindicators (Palm, et al. [23]), such asfish parasites (Galli, et al. [24]). These organisms react on specific environmental conditions or change, leading to a wide range of applications (MacKenzie et al. [25-27]; Yeomans, et al. 1997). Vidal-Martınez, et al. [22] generally distinguished between accumulation or effect bioindicators, where organisms efficiently take up substances in the former or are used to detect environmental impact in the latter. This is done while recording a definite change in their physiology, chemical composition, behaviour, or number. The presence of parasites within the environment often becomes evident after a massive infestation causing clinical signs or leading to mortality of the infected hosts. Such a situation can be combined with biotic or abiotic changes in the environment (Moller [28]), in the application of fish parasites as environmental indicators. Knowledge of the biology of the parasite and its host, the host– parasite relationship and the environment can help to detect environmental change (Vankara, et al. [29,30]).

Temperature

Parasitic worms that infect fish, and have a devastating effect on fish reproduction, grow four times faster at higher temperatures -- providing some of the first evidence that global warming affects the interactions between parasites and their hosts. Scientists found that parasitic worms infecting stickleback fish grew four times faster in experimentally infected sticklebacks raised at 20°C than when raised at 15°C. In contrast, the fish grew more slowly at the higher temperature, suggesting that fish parasites cope with higher temperatures much better than the fish they infect. The first evidence that increasing environmental temperatures can lead to a shift in the delicate balance that exists between co-evolved hosts and parasites, increasing the speed with which parasites complete their life cycles that could lead to an increase in the overall level of parasitism in natural animal populations (Macnab, et al. [31,32]).

Rainfall

Being one of the most vulnerable countries of climate change induced disasters; Bangladeshis facing some basic and major changes in its climatic behavior and weather pattern. Now a day, erratic rainfall becomes very common in Bangladesh. Climate change has induced erratic extreme rainfalls in many parts of the world. This rate is increasing abruptly. Long term unmitigated climate change will “likely” exceed the capacity of people and the natural world to adapt (IPCC [12]).Some authors conclude that a high abundance of parasites is maintained in tropical environments throughout the year (Coley, et al.[33,34]), while others suggest that these parasites could show major temporal shifts due to changes in rainfall (Steinauer, et al. [35]). Recent studies on fish infections caused by (Jiménez-García, et al. [36,37]) indicate the importance of seasonality in infection parameters of parasites in tropical ecosystems, suggesting a link between seasonal factors such as rainfall or temperature, the presence of new host cohorts and maximum variability of the infection parameters (Jawale [38]).

Humidity

Humidity is the amount of water vapor in the air. Water vapor is the gaseous state of water and is invisible. Humidity is one of the fundamental abiotic factors that defines any habitat, and is a determinant of which animals and plants can thrive in a given environment. The human body dissipates heat through perspiration and its evaporation. Heat convection to the surrounding air, and thermal radiation are the primary modes of heat transport from the body. Under conditions of high humidity, the rate of evaporation of sweat from the skin decreases. With so much blood going to the external surface of the body, less goes to the active muscles, the brain, and other internal organs (Williams [16]). Alertness and mental capacity also may be affected, resulting in heat stroke or hyperthermia (Hogan [39]). Humidity depends on water vaporization and condensation, which, in turn, mainly depends on temperature. Therefore, when applying more pressure to a gas saturated with water, all components will initially decrease in volume approximately according to the ideal gas law.

A total of 250 Wallago attu and 350 Rita rita were autopsied and examined during January 2016 to December 2017, from Swarighat under Dhaka district of Bangladesh. After collecting, the fishes were kept in an ice box with ice and carried to the Parasitology laboratory, Department of Zoology under University of Dhaka for the present observation. The information about climatic factors i.e. temperatures, rainfall and humidity were collected from “Bangladesh Meteorological Department (BMD)”, Meteorological Complex, Agargaon, Dhaka- 1207.

The environmental factors including climate, season and rainfall play an important role in the development of helminth parasites. Rising concentrations of greenhouse gases in the atmosphere are causing global climate change (IPCC [12]). Climate change may directly affect fishery production along many pathways. Fish reproduction, growth and migration patterns are all affected by temperature, rainfall and hydrology (Ficke, et al. [17]). Changes in these parameters will therefore shift patterns of species abundance and availability. Saltwater intrusion caused by rising sea levels may threaten freshwater fisheries while, at the same time, creating opportunities for catching and cultivating high-value brackish or marine species (World Fish Center [18]). Anthropogenic changes have greatly altered the fish species composition, especially of large predators at high trophic levels (Hutchings, et al. [19,20]). This has measurable effects even on life history traits, substantially changing age and size at maturation (Sharpe, et al. [21]). A conclusive description of the circumstances under which parasites can be used as indicators of environmental impact, however, still remains difficult (Vidal-Martınez, et al. [22,40]).

The aquatic environment can be studied either directly by a regular monitoring of water quality parameters or indirectly by using bioindicators (Palm, et al. [23]), such as fish parasites (Galli, et al. [41]). These organisms react on specific environmental conditions or change, leading to a wide range of applications (MacKenzie et al. [25-27]; Yeomans, et al. 1997). Vidal-Martınez, et al. [22] generally distinguished between accumulation or effect bioindicators, where organisms efficiently take up substances in the former or are used to detect environmental impact in the latter. This is done while recording a definite change in their physiology, chemical composition, behavior, or number. Also other parasite metrics such as diversity indices or species richness can be a source of information (Reuckert, et al. 2009), demonstrating a possible effect of specific environmental conditions on the fish parasite community. The presence of parasites within the environment often becomes evident after a massive infestation causing clinical signs or leading to mortality of the infected hosts. Such a situation can be combined with biotic or abiotic changes in the environment (Moller [28]), in the application of fish parasites as environmental indicators.

Temperature

Parasitic worms that infect fish, and have a devastating effect on fish reproduction, grow four times faster at higher temperatures providing some of the first evidence that global warming affects the interactions between parasites and their hosts. The study from the University of Leicester revealed that global warming had the potential to change the balance between parasite and host with potentially serious implications for fish populations. The researchers from the University of Leicester’s Department of Biology also observed behavioral change in infected fish suggesting parasites may manipulate host behavior to make them seek out warmer temperatures. And they discovered that whilst parasites grew faster in higher temperatures. In Wallago attu, in the year 2016, the observed values of temperature, humidity, rainfall, prevalence and intensity were 25.8 °C, 70%, 148 mm, 41.13% and 1.84 respectively. On the other hand, in 2017, the recorded values were temperature -26.1°C, humidity - 70%, rainfall - 110 mm, prevalence - 27.77% and intensity - 1.4 (Figure 1). In Rita rita, in the year of 2016, the observed values of temperature, humidity, rainfall, prevalence and intensity were 25.8 °C, 70%, 148 mm, 86.32% and 2.33 respectively. On the other hand, in 2017, the recorded values were temperature - 26.1 °C, humidity-70%, rainfall-110 mm, prevalence - 35.33% and intensity -4.08 (Figure 2).

Figure 1

Figure 2

In Rita rita, in 2016, the highest maximum temperature (36.2°C) were observed in the month of Sep’16 and lowest maximum temperature was 27.8 ◦C in Jan’16 while the highest prevalence (100%) were observed in the month of July’16 and lowest prevalence was 73.68% in Jan’16. In 2017, the highest maximum temperature (37.3 °C) was found in Mar’17 and lowest (28.5 °C) observed in Dec’17 and Jan’17 while the highest prevalence (57.14%) recorded in July’17 and lowest was 16.66% in May’17 (Figure 3). In 2016, the highest minimum temperature (24.5 °C) was recorded in Aug’16 while the lowest minimum was 8.2 °C in Jan’16. The highest prevalence (100%) was found in July’16 while the lowest prevalence (73.68%) was observed in Jan’16. In 2017, the highest minimum temperature (25.2 °C) and highest prevalence (57.14%) was observed in July’17 while the lowest minimum temperature (9.6 °C) was in Dec’17 and lowest prevalence (16.66%) was in May’17 (Figure 4). The highest average temperature (28.72 °C and 28.8°C) and highest prevalence (95.4% and 42.31%) were recorded during rainy season in 2016 and 2017 both. The lowest average temperature (20.75 ◦C and 20.72 °C) was recorded during winter in 2016 and 2017 while the lowest prevalence (80.62% and 29.16%) was observed during summer in 2016 and 2017 (Figure 5). In Wallago attu, in 2016, the highest maximum temperature (36.2 °C) were observed in the month of Sep’16 and lowest maximum temperature was 27.8 °C in Jan’16 while the highest prevalence (72.72%) were observed in the month of Dec’16 and the lowest prevalence was 30% in Feb’16, May’16 and Aug’16. In 2017, the highest maximum temperature (37.3 °C) was found in Mar’17and lowest (28.5 °C) observed in Dec’17 and Jan’17 while the highest prevalence (44.44%) recorded in Feb’17 and the lowest was 18.18% in Sep’17 and Nov’17 (Figure 6).

Figure 3

Figure 4

Figure 5

Figure 6

In case of W. attu, in 2016, the highest minimum temperature (24.5 °C) was recorded in Aug’16 while the lowest minimum was 8.2 °C in Jan’16. The highest prevalence (72.72%) was found in Dec’16 while the lowest prevalence (30%) was observed during Feb’16, May’16 and Aug’11. In 2017, the highest minimum temperature (25.2 °C) was observed in July’17 and highest prevalence (44.44%) was observed in Feb’17 while the lowest minimum temperature (9.6 °C) was in Dec’17 and lowest prevalence (18.18%) was in Sep’17 and Nov’17 (Figure 7). In 2016 and 2017, the highest average temperature (28.72 °C and 28.8 °C) were recorded during rainy season and the highest prevalence (44.77% and 30.8%) were found during winter. The lowest average temperature (20.75 ◦C and 20.72 °C) was recorded during winter in 2016 and 2017 while the lowest prevalence (37.95%) was observed during summer in 2016 and 24.54% during rainy season in 2017 (Figure 8).

Figure 7

Figure 8

Rainfall

Climate change has induced erratic extreme rainfalls in many parts of the world. This rate is increasing abruptly. Long term unmitigated climate change will “likely” exceed the capacity of people and the natural world to adapt (IPCC [12]). Seasonality of rainfall can exert a strong influence on animal condition and on host-parasite interactions. Some authors conclude that a high abundance of parasites is maintained in tropical environments throughout the year (Martin, et al. [34]), while others suggest that these parasites could show major temporal shifts due to changes in rainfall (Steinauer, et al. 2003). Recent studies on fish infections caused by digenean parasites (Jiménez- García, et al. [36]) indicate the importance of seasonality in infection parameters of parasites in tropical ecosystems, suggesting a link between seasonal factors such as rainfall or temperature, the presence of new host cohorts and maximum variability of the infection parameters (Soofi, et al. [42]).

In Rita rita, in 2016, the highest maximum rainfall (94 mm) were observed in the month of Aug’16 and lowest maximum rainfall was 14 mm in Mar’16 while the highest prevalence (100%) were observed in the month of July’16 and lowest prevalence was 73.68% in Jan’16. In 2017, the highest maximum rainfall (62 mm)was found in April’17and lowest (1) observed in Feb’17 while the highest prevalence (57.14%) recorded in July’17 and lowest was 16.66% in May’17 (Figure 9). In 2016, the highest minimum rainfall (1 mm) and the highest prevalence (100%) was found in July’16 while the lowest prevalence (73.68%) was observed in Jan’16. In 2017, the highest minimum rainfall (8 mm) was recorded in April’17 and highest prevalence (57.14%) was observed in July’17 while the lowest minimum rainfall (1 mm) and lowest prevalence (16.66%) was observed in May’17 (Figure 10). The highest total rainfall (271 mm and 156.75 mm) and highest prevalence (95.4% and 42.31%) were recorded during rainy season in 2016 and 2017 both. The lowest total rainfall (0 mm and 21 mm) was recorded during winter in 2016 and 2017 while the lowest prevalence (80.62% and 29.16%) was observed during summer in 2016 and 2017 (Figure 11).

Figure 9

Figure 10

Figure 11

In Wallago attu, in 2016, the highest maximum rainfall (94 mm) were observed in the month of Aug’16 and lowest maximum rainfall was 14 mm in Mar’16 while the highest prevalence (72.72%) were observed in the month of Dec’16 and the lowest prevalence was 30% in Feb’16, May’16 and Aug’16. In 2017, the highest maximum rainfall (62 mm) was found in April’17and lowest (1 mm) observed in Feb’17 while the highest prevalence (44.44%) recorded in Feb’17 and the lowest was 18.18% in Sep’17 and Nov’17 (Figure 12). In 2016, the highest minimum rainfall (1 mm) was recorded in Aug’16 and the highest prevalence (72.72%) was found in Dec’16 while the lowest prevalence (30%) was observed during Feb’16, May’16 and Aug’116. In 2017, the highest minimum rainfall (8 mm) was observed in April’17 and highest prevalence (44.44%) was observed in Feb’17 while the lowest minimum rainfall (1 mm) was in Feb’17 and lowest prevalence (18.18%) was in 2017 and Nov’17 (Figure 13). In 2016 and 2017, the highest total rainfall (271 mm and 156.75 mm) were recorded during rainy season and the highest prevalence (44.77% and 30.8%) were found during winter. The lowest total rainfall (0 mm and 21 mm) was recorded during winter in 2016 and 2017 while the lowest prevalence (37.95%) was observed during summer in 2016 and 24.54% during rainy season in 2017 (Figure 14).

Figure 12

Figure 13

Figure 14

Humidity

In Rita rita, in 2016, the highest maximum humidity (99%) were observed in the month of Jan’16 and lowest maximum humidity was 93% in Feb’16, Mar’16 and April’16 while the highest prevalence (100%) were observed in the month of July’16 and lowest prevalence was 73.68% in Jan’16. In 2017, the highest maximum humidity (100%)was found in July’17and lowest (92%) observed in Feb’17 while the highest prevalence (57.14%) recorded in July’17 and lowest was 16.66% in May’17 (Figure 15).In 2016, the highest minimum humidity (57%) was observed in Aug’16 and in R. rita the highest prevalence (100%) was found in July’16 while the lowest minimum humidity (13%) and the lowest prevalence (73.68%) was observed in Jan’16. In 2017, the highest minimum humidity (55%) was recorded in July’17 and Aug’17 and the highest prevalence (57.14%) was observed in July’17 while the lowest minimum humidity (10) was found in Feb’17 and lowest prevalence (16.66%) was observed in May’17 (Figures 16 & 17).In Wallago attu, in 2016, the highest maximum humidity (99%) were observed in the month of Jan’16 and lowest maximum humidity was 93% found in Feb’16, Mar’16 and April’16 while the highest prevalence (72.72%) were observed in the month of Dec’16 and the lowest prevalence was 30% in Feb’16, May’16 and Aug’16. In 2017, the highest maximum humidity (100%) was found in July’17and lowest (92%) observed in Feb’17 while the highest prevalence (44.44%) recorded in Feb’17 and the lowest was 18.18% in Sep’17 and Nov’17 (Figure 17).

Figure 15

Figure 16

Figure 17

In 2016, the highest minimum humidity (57%) was recorded in Aug’16 and the highest prevalence (72.72%) was found in Dec’16 while the lowest minimum humidity was 13% found in Jan’16 and the lowest prevalence (30%) was observed in Feb’16, May’16 and Aug’16. In 2017 the highest minimum humidity (55%) was observed in July’17 and Aug’17 and the highest prevalence (44.44%) was observed in Feb’17 while the lowest minimum humidity (10%) was in Feb’17 and lowest prevalence (18.18%) was in Sep’17 and Nov’17 (Figure 18). The majority of the studies on seasonal patterns of infestation of helminthes of freshwater fishes have been in the temperate climate zone of the world, with very little information available on the tropical rainy climatic zones. There has been considerable speculation on the observed temperate zone seasonal patterns, with the most significant factors being thought to be water temperature variation (Aho, etal.1982; Camp, et al. 1982; Esch, 1983; Kennedy, 1977; Granath, et al. [43]), host behavior(both dietary and social, Anderson, 1976; Kennedy, 1977; Smith, 1973)and parasite population density (Granath, et al. [5,43]; Holmes 1977).

Figure 18

The parasite which was dominant in a particular fish host, may or may not maintain its dominance in another host. Amin (1975) supports the view that the presence of a parasite species in significant number in a fish host, results in a lower density of the other species of parasites. Dogiel [44] discussed the dependence of the parasite fauna on the environment. He stated that the parasite fauna of all fishes depends on the geographical location, season, the characteristic of the water (temperature and chemical composition), type of the bottom and other biotic and abiotic factors. In W. attu, it was evident that during winter months (remarkably in December and February) maximum number of parasites were found. In R. rita, seasonal abundances of total parasite showed a distinct peak period of abundance (100%) during wet season (rainy months). This may be due to:

a) Heavy rainfall,

b) Flood,

c) Various kinds of pollutants such as, industrial pollutants, pesticides, insecticides, domestic sewage etc.

d) Decreased immunity of hosts.

This coincides with the findings of Zaman [45], Khanum and Begum [46]; where they agreed that, the seasonal abundance of the helminth parasites are significantly correlated with the seasonal rainfall (Vankara [29]). In conclusion, controlling measures should be taken to interrupt the steps of parasitic transmission from one host to another. Emphasis should be given to control the parasites with a view to increase the protein production to get her with the rapid growth of fishes. These two fishes are overburdened by huge number of helminth species because the rivers and other water bodies’ of the country are not protected. Very frequently these are polluted by flood, climatic disaster, industrial wastes, pesticides etc. Due to these environmental degradation and continuous contamination, parasitic adaptation to the hosts are increasing day by day and gaining more diversity. The present study was conducted on Wallago attu and Rita rita, collected from Swarighat, Dhaka during January 2016 to December 2017, to observe their parasite infestation of the infected and non-infected fishes with climatic factors.

In Rita rita, the highest temperature (28.72 °C and 28.8 °C) and highest prevalence (95.4% and 42.6%) were recorded during rainy season in 2016 and 2017 both. The lowest average temperature (20.75 °C and 20.72 °C) was recorded during winter in 2016 and 2017while the lowest prevalence (80.6% and 28.9%) was observed during summer in 2016 and 2017. The prevalence was found negatively correlated with temperatures (r=-0.53). In W. attu, in 2016 and 2017, the highest temperatures (28.72 °C and 28.8 °C) were recorded during rainy season and the highest prevalence (45.2% and 30.2%) were found during winter. The lowest temperature (20.75 °C and 20.72 °C) was recorded during winter in 2016 and 2017 while the lowest prevalence (38.1%) was observed during summer in 2016 and 24.4% during rainy season in 2017. The prevalence was negatively correlated with temperatures (r = - 0.49). In W. attu, in 2016 and 2017, the highest total rainfall (271mm and 156.75 mm) was recorded during rainy season and the highest prevalence (45.2% and 30.2%) were found during winter. The lowest total rainfall (0 mm and 21mm) was recorded during winter in 2016 and 2017 while the lowest prevalence (38.1%) was observed during summer in 2016 and 24.4% during rainy season in 2017.

In Rita rita, the highest rainfall (271 mm and 156.75 mm) and highest prevalence (95.4% and 42.6%) were recorded during rainy season in 2016 and 2017 both. The lowest rainfall (0 mm and 21 mm) was recorded during winter in 2016 and 2017 while the lowest prevalence (80.6% and 28.9%) was observed during summer in 2016 and 2017.In Wallago attu, in 2016, the highest humidity (99%) were observed in the month of Jan’16and lowest humidity was 93% found in Feb’16, Mar’16 and April’16 while the highest prevalence (72.72%) were observed in the month of Dec’16 and the lowest prevalence was 30% in Feb’16, May’16 and Aug’16. In 2017, the highest humidity (100%) was found in July’17 and lowest (92%) observed in Feb’17 while the highest prevalence (44.44%) recorded in Feb’17 and the lowest was 18.18% in Sep’17 and Nov’17 (Vankara, et al. [30]). The prevalence was positively correlated with humidity (r = 0.46) in different months. In Rita rita, in 2016, the highest humidity (99%) were observed in the month of Jan’16 and lowest humidity was 93% in Feb’16, Mar’16 and April’16 while the highest prevalence (100%) were observed in the month of July’16 and lowest prevalence was 73.68% in Jan’16. In 2017, the highest humidity (100%) was found in July’17 and lowest (92%) observed in Feb’17 while the highest prevalence (57.14%) recorded in July’17 and lowest was 16.66% in May’17. The prevalence was positively correlated with humidity (r = 0.51) in different months [47-52].

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