Comparative Study of the Effect of Biological Factors on Helminthes Occurrence in Oreochromis niloticus and Tilapia zilli from Lake Manzala, Port Said, Egypt

Egyptian Academic Journal of Biological Sciences is the official English language journal of the Egyptian Society of Biological Sciences, Department of Entomology, Faculty of Sciences Ain Shams University. The Journal publishes original research papers and reviews from any zoological discipline or from directly allied fields in ecology, behavioral biology, physiology, biochemistry, www.eajbs.eg.net Provided for non-commercial research and education use.


INTRODUCTION
Oreochromis niloticus and Tilapia zilli are important sources of protein food for the Egyptians.It provides about 70% of the total fish production in Egypt (EI-Zarka, 1961).Digenetic trematodes and their metacercariae take a great interest as they were one of the most widely distributed parasites infecting fish causing low weight gain, high mortality and some of them may have zoonotic importance (Hernandez et al., 1998).
Biotic factors as parasite life cycles and fish age/size and abiotic factors such as water temperature, current and/or depth also affect the distribution of parasites which may be aggregated or over dispersed in the host (Iyaji and Amana, 2015).Ramadan (1991) reported that the host species affect the rate of infection.He recorded the rate of infection in T. nilotca, T .zilliand T. galilaea fish in Lake Manzala.The highest rate of infection was found in T. zilli while, the lowest rate of infection was found in T. nilotica.
The aim of this work is to study the effect of host biological factors on the different parasitic helminthes in Oreochromis niloticus and Tilapia zilli from Lake Manzala.The sex, weight and length of fish were determined.The examination of fish revealed the presence of seven distinct defined metacercariae in addition to undifferentiated metacercariae and nematode larvae.The recovered metacercariae were Centrocestus sp., Haplorchis sp., heterophyes sp., Stictodora sp., Pygidiopsis sp., Echinostoma sp. and Phagicola sp.Results showed that O. niloticus was more susceptible to parasitic infection than T. zilli.The high est prevalence of infection was found in larger fish (weight and length) and in males (Sex) in the case of O. niloticus, while the highest prevalence of infection was found in smaller fish (weight and length) and in females (sex) in T. zilli.The occurrence of each of the helminthes gives a different response to these factors as discussed in this work.Reimchen and Nosil (2001) reported that fish males and females can differ in the levels of the infection and such differences may be mediated by the costs of sexual selection or by ecological differences between the different genders.Overall parasite prevalence was greater in males than in females.However, this excess did not occur for each species of the parasite.Hassan et al. (2012) reported that the prevalence, intensity and abundance of each metacercaria in T. zilli species showed different responses to the different factors including sex, weight and length of the host.
The aim of this work is to study the effect of host biological factors on the helminthes infecting O. niloticus and T. zilli from Lake Manzala "Port said market".

MATERIALS AND METHODS
30 specimens of O. niloticus and 30 specimens of T. zilli were collected from Lake Manzala in Port Said Governorate in ice boxes and transported to the laboratory for parasitological examination.The total length of fish were determined by measuring the distance from the tip of the longest jaw or the end of stout to the longest caudal lobe or end pushed together (Miller and Lea, 1982).O.niloticus species were divided into two length classes; as follows: Class 1 (<16cm) and Class 2 (>16cm).T. zilli species were divided into two length classes; as follows: Class 1 (<10cm) and Class 2 (>10cm).
Fish sex was determined according to Guerrero and Shelton (1974).Body cavity was opened to determine the sex, and the gonads were isolated.Small pieces of the gonads were placed on a glass slide, then pressed (squashed) with a glass cover slip and observed under dissecting microscope.
The muscles and the internal viscera including liver, kidney, gonads and digestive tract t were examined for the possible presence of trematode metacercariae (MC).These organs were kept in saline solution for few minutes for possible recover of any parasites.Tissues were screened for the presence of MC by compression method in which 0.1 gm were taken from muscles and visceral organs.Each piece was compressed between two microscopic glass slides and examined for the presence of MC (Sayasone et al., 2007;and Elsheikha and Elshazly, 2008).
Metacercariae were separately sorted out according the general features and were tentatively identified to genus level based on different morphological details; the shape of the cysts, site of infection and shape, position and contents of the execratory bladder under a light microscope (Amer, 1996;Saad, 2007;Elsheikha and El-shazly, 2008;Sohan et al., 2009;Taher, 2009;Pinto andDe Melo, 2012 andMotarjemi et al., 2013).
The prevalence, mean intensity and abundance of recovered helminthes according to each factor considered were calculated according Margolis et al. (1982).To satisfy the assumption of the statistical analysis used, all the data were normalized by log (x+1) transformation to achieve linearity.For studying the significant differences between groups, analysis of variance was used.All data were analyzed with the software packages Microsoft SPSS version 15.0, for statistical evaluation.Values of P < 0.05, P< 0.01and 0.001 reflected levels of significance.

RESULTS AND DISCUSSION
The examination of fish revealed the presence of seven distinct defined metacercariae in addition to undifferentiated metacercariae and nematode larvae.The recovered metacercariae were Centrocestus sp., Haplorchis sp., heterophyes sp., Stictodora sp., Pygidiopsis sp., Echinostoma sp. and Phagicola sp.Nematode larvae and Phagicola sp. were specific for T. zilli while, heterophyes sp. was specific for O. niloticus.
The highest total prevalence was recorded in O. niloticus 86.7% higher than in T. zilli 83.7%.Regarding prevalence of different species of helminthes, the highest prevalence was recorded in both species for undifferentiated metacercariae followed by Centrocestus sp.The total abundance was higher in O. niloticus1527.3±461.1 than in T. zilli 674.8±214.7, the highest abundance was recorded in both species for undifferentiated metacercariae followed by Centrocestus sp. in O. niloticus and Echinostoma sp. in T. zilli.The total intensity was higher in O. niloticus1762.3±517.6 than in T. zilli 788.8±241.9, the highest intensity was recorded in both species for undifferentiated metacercariae followed by Centrocestus sp. in O. niloticus and Haplorchis sp. in T. zilli.Regarding prevalence, abundance and intensity with different species of helminthes are shown in Table (1).In our study O. niloticus was more susceptible to parasitic infection than T. zilli and this agrees with (Taher, 2009) who recorded that the rate of prevalence in O. niloticus and T. zilli collected from Assiut Governorate was 84.75%, and 78.25%, respectively.Ramadan, 1991 recorded that the highest percentage of infection was found in T. zilli 67.6% and the lowest in O. niloticus 47.4% this variation may be due to a multiple reasons such as host species, different habits, food type, the presence and absence of snails and birds which plays an important role in the life cycle of many helminths and also the differences in the seasons in which the samples were collected.
The effect of fish length on the prevalence, abundance and intensity of different helminthes infecting O. niloticus and of T. zilli is shown in Table (2).
In O. niloticus, the results showed that prevalence was the highest (84.2%) in fish within length class 2 (>16) and lowest (81.8%) in fish within length class 1 (<16), while, in the case of T. zilli the prevalence was the highest (90%) in fish within length class 1 (<10) and the lowest (70%) in fish within length class 2 (>10).Mobedi (2001) stated that the decrease in the prevalence of infection in the larger fish could be a result of the increase in resistance to diseases of the host with the increase in length and differ of feeding habit of the host.Similar view is confirmed by Grutter et al. (2002).In O. niloticus, the highest total mean abundance of infection (2203.7±675.7)was recorded in fish within length class 2 (>16) and the lowest (359.1±215.3) in fish within length class 1 (<16) (P<0.001) and in T. zilli the highest total mean abundance of infection (882±527.3)was recorded in fish within length class 2 (>10) and the lowest (545±177) in fish within length class 1 (<10).In this work there was a direct relationship between abundance and the host length and this agrees with Blackburn and Gatson (1997) who recorded relationship between parasite abundance and body total size, this in turn may be attributed to the more specialized immunity of these fish with size and age.
In O. niloticus, the highest total mean intensity (2616±760.6)was recorded in fish within length class 2 (>16) and the lowest (395±234.7) in fish within length class1 (<16) (P<0.001) and the same in T. zilli as the highest total mean intensity of infection (1461.7±816.2) was recorded in fish within length class 2 (>10) and the lowest (794±307.7) in fish within length class1 (<10) (P˂0.05).This disagrees with Hassan (2012) who found that the total mean intensity of infection is inversely proportional to T. zilli and O. niloticus length.
The effect of fish weight on the prevalence, abundance and intensity of different helminthes infecting O. niloticus and of T. zilli is shown in Table (3).
In O. niloticus, the results showed that prevalence was the highest (100%) in fish within weight class 2 (>32) and the lowest (83.3%) in fish within weight class 1 (<32) and reversibly in T. zilli as the prevalence was the highest (95.8%) in fish within weight class 1 (<16) and lowest (55.6%) in fish within weight class 2 (>16) and this may be due to the immune response as discussed previously.
In O. niloticus, the highest total mean abundance of infection (5241.7±1285.83) was recorded in fish within weight class 2 (>32) and the lowest (598.8±240.2) in fish within weight class 1 (<32) (P<0.001) and this also repeated in T. zilli as the highest total mean abundance of infection (688.9±585.2) was recorded in fish within weight class 2 (>16) and the lowest (643.8±176.03) in fish within weight class 1 (<16).In O. niloticus, the highest total mean intensity of infection (2616.9±760.6)was recorded in fish within weight class 2 (>32) and the lowest (718.5±281.6) in fish within length class1 (<32) (P< 0.001) this agrees with Bell and Burt (1991), Machado et al. (1994), Takemoto and Pavanelli (1994), Poulin (1995), Fiorillo and Font (1996) and luque et al. (1996 a&b) who found that increased size and age of fish result in significant increase in the levels of parasitism.This also occurred in T. zillias the highest total mean intensity of infection (1537.5±1273.9) was recorded in fish within weight class 2 (>16) and the lowest (880±266.95) in fish within length class1 (<16).
The effect of fish sex on the prevalence, abundance and intensity of each of the different helminthes infecting O. niloticus and of T. zilli is shown in Table (4).N = number of examined fish, n = number of infected fish.
In O. niloticus, Results showed that the prevalence with metacercariae was higher in male specimens (91.7%) than in female ones (83.3%) and reversibly in T. zilli as the prevalence was the highest in female specimens (100%) than in male ones (64.3%).Comparing abundance values showed that the total mean abundance of infection was higher in males (1845.8±708.1)than females (1315±617.6) in O. niloticus while, infection was higher in females (955.6±359.4)than males (316.4±141.4) in T. zilli.Finally the intensity values showed that the total mean intensity of infection was higher in males (2013.6±753.5)than females (1578±725.4)(P˂0.001) in O. niloticus and reversibly in T. zilli as the intensity was the highest in female specimens (1315.5±489.5)than in male ones (448±248.5).Emere (2000) revealed differences in infestation between males and females to differences in feeding which could be in terms of quality and quantity.It could also be attributed to differences in the degree of resistance to infestation.Males are usually more sensitive to the parasites than females partially due to testosterone synthesis, which might cause decreasing immune competency (Gbankoto et al., 2001).
In conclusion, O. niloticus was more susceptible to parasitic infection than T. zilli and the incidence of parasitic infections recorded in the present study was markedly high and showed different responses to the biological factors that varied according to parasite species and fish host.
niloticus and T. zilli of Lake Manzala according to host species.n = number of infected fish.
Malek and

Table 2 :
Prevalence, mean abundance (±SE) and mean intensity (±SE) of helminthes infecting O. niloticus and T. zilli of Lake Manzala according to host length.
N = number of examined fish, n = number of infected fish.

Table 3 :
Prevalence, mean abundance (±SE) and mean intensity (±SE) of helminthes infecting O. niloticus and T. zilli of Lake Manzala according to host weight.

Table 4 :
Prevalence, mean abundance (±SE) and mean intensity (±SE) of helminthes infecting O. niloticus and T. zilli of Lake Manzala according to host sex.