Copepoda parasites in economically important fish , Mugilidae ( Mugil cephalus and Liza falcipinnis from Lac Nokoue Lagoon in Republic of Benin , West Africa

Fish parasitology is an indispensable tool in aquatic health studies and a basic understanding of richness of a community parasitism in many localities is essential for instituting control. Many copepod parasites are ecto-parasites which negatively affect the appearance and reduced production of species of economically important fish, both from the wild and fish farms, thus making them difficult to market. In this study, copepod parasitic investigation was carried out in gills of 856 fish mugilidae (Mugil cephalus and Liza falcipinnis) in three stations (Ganvie, Djdje and Zogbo) of Lac Nokoue lagoon. In the three stations, three species of parasitic copepod were found: Nipergasilus bora, Ergasilus latus and Ergasilus lizae. The highest total percentage copepod prevalence was found in Ganvie (86.23%) and the least in Djdje (63.14%). There is significant difference (P<0.05) in the rate of infestation of L. falcipinnis at Djdje than the other two stations, where as M. cephalus shows no significant difference in the rate of infestation in the three stations. The research reveals higher number of parasite copepods during the rainy season.


INTRODUCTION
Even though spawning can be induced on an environmental basis, mullet farming still depends on fry or fingerlings stocked from natural water.This fact combined with behaviour of mullets, promotes disease including parasite infestation (Paperna and Overstreet, 1981).This results in constant dissemination of disease-causing agent between cultured and natural population of mullet.Transmission can occur through water and intermediate host.Thus there is need for comprehensive study of parasites from natural stocks.
Lake Nokoue is the largest coastal lagoons and the most productive brackish water body in Republic of Benin (Laleye and Moreau, 2004).Lake Nokoue was formally a lake until 1185 when it was artificially linked with the ocean through a channel (Lang and Paradis, 1977).Majority of fish production (fish mugilidae inclusive) come *Corresponding author.E-mail: adenike63@yahoo.com.from the lagoon (Laleye et al., 2003;Niyonkuru et al., 2010).
The Ganvie area is located near the floating village of Ganvie, where the water is characterised by a high level of organic pollution (Niyonkuru et al., 2003).The fishing technique used by the fishermen from whom samples were obtained included gill nets, cast nets and acadjas (a traditional fish harvesting system using nets to encircle man-made brush packs of branches placed in the lagoon (Gnohossou et al., 2009).
Fish mugilidae are economically important and are important food fishes.The euryhalinity, eurythermality and their simple diet as well as their rapid growth, have made them the object of aquaculture in many parts of the world (Oren, 1981).In Republic of Benin, these (Mugil cephalus and Liza falcipinnis) constitute important proportion of catches by artisanal or subsistence fishermen (Laleye et al., 2003;Gnohossou, 2009).They are of economic importance to the country.
Parasites have recently been highlighted as serious pathogenic problems in cultured mullet fish in marine and brackish water.Among the parasites, copepode family is commonly found on fishes cultured in brackish water (Noor El-Deen et al., 2012), and therefore a threat to the developing industry of finfish mariculture (Ru¨ckert et al., 2008).
Copepods are aquatic crustaceans which are diverse and are the most numerous metazoans in the water community with habitats ranging from fresh water to hypersaline conditions.Some copepods parasites of fishes all over the world may cause lesions that negatively affect the fisheries and aquaculture economies (Barreiro and Francnete, 2003).
Some studies have been carried out to discover the richness of community parasitic in many localities (Poulen and Rode, 1997;Sures and Street, 2001;Kimpela et al., 2006;Boualleg et al., 2011) In Republic of Benin, many researchers have worked on parasites of fish (Doussou, 1985;Sakiti et al., 1991;Sakiti, 1997;Gbankoto et al., 2003) but no work has been carried out on parasites of mugilidae fish in Repulic of Benin.
The objective of this study is to determine copepod parasites in economically important fish Mugil cephalus and Liza falcipinnis in some major fishing areas of the largest fishing lagoon in Republic of Benin.
In determining the copepods parasite species of this world economically important fish with high commercial and environmental attributes will provide better culture condition for them, especially in mariculture.This will also help to solve some of the problems of fish diseases that can perturb their health and productivity, both in the wild and fish culture.

MATERIALS AND METHODS
The study site, Lake Nokoue (Figure 1) is the largest lagoon (Moreau, 2004), is a shallow, sub-tropical coastal lagoon (6°25N, 2°36E) (Table 8) with surface of 150 km and stretches 20 km in its east-west direction by 11 km in the north-south direction (Laleye et al., 2003).Lake Nokoue opens directly into the Atlantic Ocean through channel at cotonou which is about 24.5 km long.
For the purpose of this study, three stations were considered as sampling areas within the lagoon: Ganvie, Djdje and Zogbo (Figure 1).The Ganvie area is located at the northern part of the lake Nokoue lagoon, near the floating village of Ganvie where the water is characterised by a high level of organic pollution (Laleye et al., 2003).The Djdje and Zogbo areas are located at the southern part of the lake and are partly influenced by Atlantic Ocean waters.Sampling was carried out at each station both in the dry (December-March, 2011) and the rainy season (April-July, 2012).

Collection and analysis of water samples
Water samples were collected with 1 dm 3 water samplers and stored in 1 L water bottles and analysed in the laboratory for pH, conductivity, salinity and turbidity using a multi-meter water checker (Horiba U-12).Water sample was collected in 250 ml dissolved oxygen bottle and fixed with Winkler solution at each station.This was followed by dissolved oxygen estimation using Iodometric Winkler's method.Water temperature was measured in situ using mercury-in-glass thermometers.

Sampling of the fish specimen and parasitological examination
M. cephalus and L. falcipinnis from the three stations were obtained by the assistance of fishermen.A total number of 856 fish specimen, M. cephalus and L. falcipinnis were examined for copepods parasites.In Station 1 (Ganvie) number of fish examined was (MC -115, L.F -132), in Station 2 (Djdje) it was (MC -181, LF -226) and station 3 (Zogbo) it was (MC -96 and LF -106).The collected fish were transported in ice boxes to the laboratory and examined for parasites.The weight of the fish were taken using digital weighing balance and recorded.The standard length (SL), the total length (TL) and the fork length (FL.) were measured with the aid of meter rule.
After dissection, stereo-microscopic observation was made on gills, for the presence of copepod parasites.Checking of prepared slides for parasites for better observation was carried out using light microscope.The standard length (SL), the total length (TL) and the fork length (FL) were measured with the aid of meter rule.The host species was identified using Fisher et al. (1987).The standard length (SL), the total length (TL) and the fork length (FL) were measured with the aid of meter rule.The host species was identified using Fisher et al. (1987).Collected copepods were fixed and preserved in ethanol (70%).Copepods on gills were studied using stereo and light microscopy.Parasites species identification was based on morphological features according to Yamaguti (1963), Vassiliades, (1975), Kabata (1979) (Skryabin et al., 1982), Ben-Hasseine (1983), Kabré (1997), Kabre et al. (1997), Ho and Kim (2004) and Moravec (2007).

Data analysis
The parasitological terms follow Bush et al. (1997): prevalence (P) is the number of fish infected with one or more individuals of a particular parasite species (or taxonomic group) divided by the number of hosts examined (expressed as a percentage): Intensity (of infection, I) is the number of individuals of a particular parasite species in a single infected host (expressed as a numerical range); mean intensity (of infection, mI) is the average intensity, or the total number of parasites of a particular species found in a sample divided by the number of infected hosts: ANOVA test, using statistical software (SPSS) was also done on MC and LF to know the significant difference of copepod parasites infestation in each station.

Physicochemical parameters of the study area
The physicochemical parameters recorded at the three stations during rainy and dry seasons are presented in Table 1.Both in the rainy and dry season, the salinity levels were lowest in station 1 (Ganvie) with 0 and 11.4 parts per thousand, but highest in station 2 (Djdje) with 0.8 and 29.5 parts per thousand salinity levels respecttively.The highest salinity recorded at Djdje is because of its proximity to the sea.The lowest salinity value obtained   can be explained by the proximity of the So River to the station (Laleye et al., 2003).Generally low conductivity levels were recorded from all stations during rainy season, whereas relatively high levels which ranged from 19.5 mScm -1 in station 1 to 46.5 mScm -1 at station 2 were obtained in the dry season (Table 1).On the other hand, every station had higher turbidity, pH and DO levels during rainy than dry season (Table 1).
Figures 2 to 7 shows graphs of parasitic copepod species (E.latus, N. bora and E. lizae) found in both LF and MC in all the stations.

DISCUSSION
Generally low conductivity levels were recorded from all stations during rainy season, whereas relatively high levels which ranged from 19.5 mScm -1 in station 1 to 46.5 mScm -1 in station 2 were obtained in the dry season (Table 1).On the other hand, every station had higher turbidity, pH and DO levels during rainy season than dry season (Table 1).This report coincides with that of Yakub et al. (2011).
Copepod parasites are common on fish hosts in        (2003), who worked on parasite copepod from fishes of Santa Cruz Channel and Suape area of Pernathatmbico, Brazil.He discovered that, 66% family mugilidae were infested with copepod parasite The highest total percentage copepod parasites recorded in Ganvie might have been caused by organic pollution resulting from the human settlement.Aladetohun et al. (2013, awating publication), in a similar work on copepod parasites of these species of mugilidae fish from Lagos lagoon, Nigeria also shows that ,Liza falcipinnis had more copepod parasites than Mugil cephalus.
In this work, genuss Nipergasilus bora copepods had the highest frequency of occurrence and relative abundance than genus ergasilus.This agrees with Morella and Garippa (2001) in his work on parasites of grey mullets from Mistras lagoon, Western meditarranean, also reported Caligus apolus and Nipergasilus bora to be the most prevalent crustaceans.Ben-Hassin (1983) in his work on copepod parasites of mugilidae from the meditarrranean of France and Tunisia, reported Nipergasilus bora.Although Ergasilus lizae and Ergasilus latus were also found in all the three stations.Perperna and Lahav (1971), also discovered copepod parasite (Ergasilus lizae) in grey mullets in Israel.
Tores and Bareiro (2003) in his work also revealed higher no of copepod parasites during rainy season which also agrees with the result of this present work Yashouv, 1972, reported reduction in the number of harvested fish was about 50% of those stocked, rather than the expected 90% as a result of this infestation.Even though M. capito, Tilapia aurea and carp accompanied M cephalus, only M cephalus was involved in mortalities.Individual M. capito had about nine copepods compared with 100 to 120 on the emaciated M. cephalus.
In conclusion, high level of copepod parasites infestation of mugilidae fish (Mugil cephalus and Liza falcipinnis) in Lac Nokoue can cause serious health problems, fish mortalities and consequent production loss.

Figure 1 .
Figure 1.Location of Lake Nokoue showing fish sampling stations.

Table 1 .
Spatial and seasonal distributions of the physico-chemical parameters in some parts of Lake Nokoue.

Table 2 .
Copepods for eight months in Benin.

Table 3 .
Percentage fish infested and percentage parasite prevalence in Benin.

Table 4 .
Prevalence rate of copepod during dry and rainy season.

Table 5 .
Prevalence rate of copepod species of Ganvie.

Table 6 .
Prevalence rate of copepods species of Djdje.

Table 7 .
Prevalence rate of copepods species of Zogbo.

Table 8 .
Geographical coordinate of sampling stations and eventually result in the death of fish and significant economic loss.In his work he also reported maximum copepoda parasite infestation was noticed in M. cephalus and Lates calcarifer (P.Vinnobaba 2007).The result of this work agrees with that of Barreiro and Fancinete,