SEASONAL VARIATIONS IN CONDITION FACTOR OF TWO FRESHWATER FISH SPECIES BELONGING TO THE GENUS SCHILBE OKEN, 1817 (SCHILBE MANDIBULARIS AND S. INTERMEDIUS) IN AN ESTUARINE ECOSYSTEM, AGHIEN LAGOON (CÔTE D’IVOIRE, WEST AFRICA)

Gustave N’guessan ALIKO, Charles Koffi BOUSSOU, Félix Koffi KONAN and Yves Kotchi BONY. Department of Environment, Jean Lorougnon Guédé University, Daloa City (Côte d‟Ivoire). ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

We studied changes in condition factor (CF) of two fish species belonging to the genus Schilbe: Schilbe mandibularis and S. intermedius in the estuarine system of Aghien Lagoon. Fish populations were sampled monthly during one year from July 2014 to June 2015. Samplings were performed by experimental fishing using gillnets. Means of condition factor were determined for the four climatic seasons that characterize the study site. Results indicated that the global condition factor including both climatic seasons was significantly higher in S. mandibularis than that obtained in S. intermedius (p˂0.05). Condition factor showed high variations (p˂0.05) between climatic seasons in S. mandibularis. The highest average (CF = 2.83) was recorded in the long dry season while the lowest (CF = 0.09) was obtained in the short dry season. Concerning S. intermedius, condition factor showed relatively low variations but differed significantly (p˂0.05) between climatic seasons. The highest average (CF = 0.80) occurred in the long wet season while the lowest (CF = 0.16) occurred in the long dry season. We concluded that the condition factor of these two species exhibited very different seasonal trends in the Aghien Lagoon.
In the Aghien Lagoon, the Schilbeidae family was represented by four species (Parailia pellucida, Parailia spiniserrata, Schilbe mandibularis and Schilbe intermedius) among which S. mandibularis and S. intermedius were the most abundant. In addition, these two species were among the fish most targeted by the artisanal fishing in this freshwater lagoon.
The condition factor which show the degree of well-being of the fish in their habitat is expressed by "coefficient of condition" also known as length-weight factor. This factor is a measure of various ecological and biological factors 1334 such as degree of fitness, gonad development and the suitability of the environment with regard to the feeding condition (Anene, 2005;Ndimele et al., 2010).
In fisheries sciences, the condition factor is used in order to compare the "condition", "fatness" or wellbeing of fish. It is based on the hypothesis that heavier fish of a particular length are in a better physiological condition (Bagenal et al., 1978). Condition factor is also a useful index for monitoring of feeding intensity, age, and growth rates in fish (Ndimele et al., 2010). The condition factor of fish can be affected by a number of factors such as stress, sex, season, availability of feeds, and other water quality parameters (Khallaf et al., 2003). It is strongly influenced by both biotic and a biotic environmental conditions and can be used as an index to assess the status of the aquatic ecosystem in which fish live (Anene, 2005). Condition factors of different tropical fish species were investigated and reported by several studies (Abowei and Davies, 2009; Alfred-Ockiya and Njoku, 1995). Indeed, condition factor has been used as an indicator of health in fishing biology studies since the beginning of the 20 th century, such as growth and feeding intensity (Froese, 2006).
This study aimed to describe the changes that occurred in the condition factor of Schilbe mandibularis and S. intermedius during the four climatic seasons that characterize the Aghien Lagoon.

Study site:-
The Aghien Lagoon is located in the Southeastern of Côte d'Ivoire between latitudes 5°22'N and 5°26'N and longitudes 3°49'W and 3°55'W ( Fig. 1). This lagoon is located to the north of the Ebrié Lagoon from which it is separated by the Potou Lagoon. The Aghien and Potou Lagoons communicate through a natural channel (Koffi et al., 2014). The Aghien Lagoon could reach 11 m deep (Guiral and Ferhi, 1989). This lagoon covers an area of 20 km² for a perimeter of 40.72 Km. It is supplied by two main tributaries, Djibi and Bété Rivers, and is almost exclusively continental all year long. This gives to the hydrosystem a fluvial character (Koffi et al., 2014). Located in an estuarine zone, the ichthyological diversity of this lagoon is strongly influenced by species of marine and continental origin. The result is a very diverse fish community with intense fishing activity (Bédia et al., 2009;Traoré et al., 2014). The Aghien Lagoon is subject to an equatorial climate characterized by four seasons (Durand and Chantraine, 1982). The monthly distribution of these seasons is shown in Table 1.
Data Sampling:-Fish populations were sampled monthly during one year from July 2014 to June 2015. Three sampling areas were chosen along the longitudinal axis of the lagoon (From the mainland at the mouth of the Djibi and Bété Rivers, to the Potou Lagoon). Thus, we had: the upstream sector (05°24.91"N -03°53.74"W and 05°25.66"N -03°54.23"W), the median sector (05°25.36"N -03°53.75"W and 05°24.95"N -03°52.50"W) and the downstream sector (05°24.18"N -03°50.91"W and 05°23.21"N -03°50.49"W). This choice of sampling sites was selected to cover a fair degree of habitat heterogeneity in Aghien Lagoon.
Data were collected through experimental fishing using gillnets of various mesh sizes (from 10 to 40 mm). The 3 sectors were sampled during each survey. Fishing was done overnight (17.00 to 7.00) and during the day (7.00 to 13.00). Where: W = the weight of fish in gram (g), SL = the standard length of fish in centimeter (cm), a = exponent describing the rate of change of weight with length (= the intercept of the regression line on the Y axis), b = the slope of the regression line also designed as allometric coefficient.
The condition factor (CF) was determined by using the following equation (Gomiero and Braga, 2005): CF = 100W/SL b b = the value obtained from the length-weight equation. The exponent "b" value, that is equal to 3, was not used to calculate the "CF" value. Bolger and Connolly (1989) claim that it is not a real representation of the length-weight relationship for greater majority of fish species. Therefore the "b" value used was obtained from the estimated length-weight relationship equation (W = a*SL b ) as suggested by Lima-Junior et al. (2002).
Seasonal variations of condition factor in Schilbe mandibularis and S. intermedius were compared among climatic seasons using all of data from samples obtained in both study stations. A mean value of the condition factor was calculated for each species at different season. And Seasons were compared using the parametric Anova test (Oneway analysis of variance) once the variances were shown to be homogeneous (Levene"s test). For two-by-two comparisons, the Tukey's pair wise test was used. The minimum significant level for the relevant test was set at p<0.05. The statistical analyzes were carried out using the PAST 3.14 software.   The global length-weight relationships performed for both seasons indicated that the regression equation varied significantly (p ˂ 0.05) between the two species (Tab. 4).
The seasonal length-weight relationships obtained for each species are presented in tables 5 and 6. Concerning S. mandibularis, the slope of the regression (b) ranged from 2.554 (LDS) to 3.865 (SDS). For S. intermedius, b ranged from 3.138 (LWS) to 3.672 (LDS).

Variations in condition factor:-
The annual average of the condition factor was higher (p ˂ 0.05) in S. mandibularis (CF = 0.84) than that recorded in S. intermedius (CF = 0.29). Overall comparison of seasonal condition factor between the two species is illustrated in figure 2.
In S. mandibularis population, condition factor showed a high decrease from LDS to SDS with mean values of 2.83 and 0.09 respectively. A low increase was recorded from SDS to SWS. For S. intermedius, seasonal variations of condition factor were relatively low. Condition factor increased from LDS to LWS and decreased in SDS. For this species, the averages of condition factor were less than 1 at both seasons. Condition factor values are presented in

Discussions:-
For both species, fish sizes varied significantly from one climatic season to another. This implies great variability in the proportions of the different stages of fish development during the year. The mean sizes were higher in LDS and lower in SDS for Schilbe mandibularis. Concerning S. intermedius, mean sizes were higher in LWS and lower in SDS. Moreover, the maximum sizes recorded in the Aghien Lagoon for the two species (204 and 174 mm SL respectively for Schilbe mandibularis and S. intermedius) were lower than those observed by De Vos (2003) in the continental African waters (300 and 500 mm SL respectively for Schilbe mandibularis and S. intermedius).
Overall, LWR differed significantly between the two species. Consequently, these two species belonging to the same genus showed a very different growth. Knowledge on length-weight relationships of fish helps in predicting potential yield and determination of size at capture for obtaining optimum yield, as these parameters are directly related to weight of the fish (Le Cren, 1951; Chonder, 1972). According to Martin (1949) the values of the exponent "b" usually remain between 2.5 and 4.0 and in majority of the cases the value was not equal to "3". Our results coincide with the interval of 2.5 -4.0 ("b" ranged from 2.554 to 3.865 for S. mandibularis and ranged from 3.138 to 3.672 for S. intermedius).
The condition factor varied significantly between climatic seasons for both species. This result would probably be a consequence of the large variation in fish sizes between climatic seasons. Indeed, condition factor is influenced by the stage of sexual maturity and this maturity depends on the stage of development of the fish. According to Bagenal and Tesch (1978), the range 2.9 -4.8 is the recommended condition factor as suitable for matured fresh water fish. Our results showed that fish condition factor ranged from 0.04 to 4.46 for S. mandibularis. For S. intermedius condition factor varied from 0.06 to 1.00. In the Taabo Lake (Bandama Basin, Côte d"Ivoire), Aliko et al. (2015) reported that condition factor in S. mandibularis ranged from 1. Seasonal condition factor was highest in LDS while it was lowest in SDS for S. mandibularis. According to Ouattara et al. (2008), S. mandibularis in the Bia River reproduced in the rainy season from April to June and from August to October. These authors added that maximum breeding activity of S. mandibularis occurred from April to June, corresponding to the peak of rainfall. The high condition factor values of LDS could be explained by a high proportion of gonad-maturing individuals for breeding in the following season, which corresponds to the long rainy season. Concerning S. intermedius, the highest seasonal condition factor was recorded in LWS while the lowest occurred in LDS. In the Pendjari River (Benin, West Africa), Montcho et al. (2011) indicated that spawning of S. intermedius lasted from June to November, coinciding with peaks in rainfall and flooding. The LWS period, which had high condition factor values, coincided partially with the spawning period of S. intermedius as reported by Montcho et al. (2011). We could conclude that the condition factor for these two species belonging to the same genus exhibited very different seasonal trends in the same lagoon.