Biodiversity of Freshwater Shrimp of the Genus Macrobrachium (Decapoda Palaemonidae) in the Nyong Basin of Cameroon

The population of shrimps, especially the macrobrachium genus, has been affected with habitat pollution and overexploitation. Shrimps provide a major protein source to animals higher in the food chain. The importance of studying the ecology of shrimps in their different habitats helps in their preservation and provides possibilities of carcinoculture. This study examines diversity, ecology and reproduction parameters of fresh water shrimps of the genus macrobrachium in the basins of Lepmassoun and Ondoamedza rivers. Lepmassoun and Ondoamedza rivers form part of the larger Nyong river basin in Cameroon. In situ water physicochemical parameters were determined on site, preserved water samples used in mineral analysis and subsequent ecological health assessment. Shrimps were sampled using the scoop method with hand nets and analyzed. Sampling was done in 5 seasons distributed from January 2017 to February 2018. The results of physicochemical parameters indicate that water in the two rivers was slightly mineralized, sufficiently oxygenated and slightly turbid. It was generally a non-polluted ecological zone for shrimps. A total of 113 shrimps distributed among 14 species were collected. The shrimp population included Macrobrachium macrobrachion Macrobrachium idae, Macrobrachium rude, Macrobrachium niloticus , Macrobrachium dux Macrobrachium sp1, Macrobrachium sp2, Macrobrachium sp3,Macrobrachium sp4, Macrobrachium sp4, Macrobrachium sp5, Macrobrachium sp6, Macrobrachium sp7, Macrobrachium sp8 and Macrobrachium sp9.In the river Odoameza 11 species were collected among which Macrobrachium sp8 (26.02%) is abundant, though,in the river Lepmassoun we collected 10 species dominanced by Macrobrachium macrobrachion (22,5%). The species Macrobrachium macrobrachion is most ubiquiste throughout river Lepmassoun (%O = 83.33%) The river basin of Lepmassoun had a higher population of Macrobrachium macrobrachion with a percentage occurrence of 66.67%. then It is concluded that the water in the two river basins is of good ecological quality for shrimp survival with species Macrobrachium macrobrachion dominating in the river lepmassoun. In the river Ondoameza Macrobrachium sp8, Macrobrachium idea, Macrobrachium macrobrachion,Macrobrachium sp4 having all the percentage of occurrence (%O) of 66.67% are relatively represented. Only Macrobrachium dux have Ovigerous females in our study. This Ovigerous females ranged from 50.38 to 64.18 mm and egg size varied from 1.7 to 2 mm. The prawn attained a maximum total length and weight of 64,18 m and 2,96 g respectively. In our basins slope the Macrobrachium dux reproduces twice year during the big dry season and small dry season since production is early and the eggs are rather broad by consequence the larval development is shortened.


INTRODUCTION
The world production of shrimp exceeded 240 T in the year 2000, wh ich roughly corresponds to 20% of the total quantity produced (Sampaio, Silva et al. 2007).Africa's contribution to shrimp production remains very minimal with almost null part icipation in carcinoculture (FAO 2010). The ma in species of fresh water shrimp with commercial value belongs to the family paleamonidae (Nnana Noah, 2010). Within this co mmercially v iable family, the genus Paleamon, Leander, and Macrobrachium are do minant (Monod 1966). Furthermore, Macrobrachiu m (Bate, 1868) has been found in most of the biogeographic areas and more than 240 species have been recorded (De Grave and Fransen 2011).
Overfishing and pollution affects biodiversity of aquatic animals (Omwo ma 2012). Continuous aquatic system assessment for water quality and biodiversity helps in system management and product quality. Use of agricultural products such as pesticides and fertilizers including urbanizat ion are known to affect water quality and species diversity (Allan and Flecker 1993). The fact that production of shrimp in Africa has remained low leads scientists to determine possible reasons and mitigation measures over the same. This is particularly the case given that Africa is dominated with several fresh water bodies that are conducive for shrimp production.
Furthermore, shrimps are of great ecological, medical and socio-economic interest. They can be characterized by their life cycle (New and Singholka 1985) and they play a significant ro le in water t rophic networks. They are regarded as indicators of good water quality. In addition, the market of shrimps in the east is a gold basket and their price is higher than fish. Such good qualities of shrimps makes them an important subject of study especially their ability to provide high protein content in different diets (Doume doume, Toguyen et al. 2013).
In Cameroon, shrimps of the genus Macrobranchium (Herklots 1851) might be exp loited by art isanal fishermen that use bow nets. There is little data available on the ecology and the biology (reproduction) of shrimps in Cameroon (Dou me dou me, Toguyen et al. 2013), (Tchakonte , Ajeagah et al. 2014)and (Ajeagah, Yogback et al. 2017), (A jeagah, Yogback et al. 2018). As such we endeavor herein to characterize the ecology of shrimps river Lep massoun and the river Ondomedza . Lep massoun and Ondoamedza rivers form part of the larger Nyong river basin in Cameroon. The study considers biodiversity of shrimps and ecological quality parameters of the two river basins. Fig.1: Study areas that comprise of River Lepmassoun and River Ondoamedza along River Nyong in Cameroon.  are sampling points on Lepmassoun River while Ond 1-3 are sampling points along the Ondoamedza River. The study site, Nyong River Basin, co mprises of two tributary rivers namely Lep masoun and Ondoamedza (Fig.  1). These two river tributaries lie within an equatorial climate. Such a climate is characterized with four main seasons per year (two d ry seasons and two wet seasons ). The main dry season is experienced fro m December to February wh ile the main wet season is experienced fro m September to November. The rain fall distribution ranges fro m 3 000 mm per month to 1500 mm per month in the two basins resulting to the entire area being covered with forest (Olivry 1986). Six stations were identified as marked in Fig. 1 ' 18,166' ' N; 1132' 37,413'' E) fo r the river Ondoamedza (see Fig. 1).

Physicochemical parameters determination
Physicochemical parameters including Temperature, Dissolved Oxygen, pH, Electric Conductivity and TDS were determined insitu. Dissolved CO2, Alkalin ity (HCO3 -), Nitrates (NO3 -), Nitrites (NO2 -), Orthophosphate (PO4 3-), and A mmon iacal Nitrogen (NH3-N) were determined using standard procedures on unfiltered water samples. Shrimps were collected using a scoop method with a hand net and preserved with formalin in containers that had been washed with alcohol (95%). In the laboratory, the shrimps were identified by placing them in a petri dish, sorted accorded to their morphology and identified using a binocular magnifying g lass according to cited keys of identification features (Monod 1966), (Powell 1980); Won and Lawrence, 1988; Bruce and Thomas, 1991; (Day, Stewart et al. 2001)).

Determination of Shrimp biodiversity
The diversity index of (Shannon and Weaver 1948)
The index of Shannon and Weaver in the river Lep massoun is of 2.05 bit/indiv idual and that of Piélou is 0.57. These indices varied respectively in this river of 1.06 (Lma1) to 2.

Reproduction of Macrobrachium dux Determination of the sex-ratio and rate of femininity
All in all, the females are more numerous than the males. During the period of study 5 individuals of Macrobrachium dux were co llected either 3 individuals (4 females and 1 males) in the river Lep massoun giving a sex-ratio of 0.25. Fro m a campaign to another in the river Lep massoun the sex-rat io at this species varied from 0 (PSS) with 0.5 (GSS 2017) and the females are dominant except during the small dry season where the males are equal to the females. Genrally, the rate of feminity (TF) during all the period of study in the river Lep massoun is 57.14%, it varied fro m 66, 67% (GSS2017) to 100 % (PSS) ( Table V).

Fruitfulness and gonado-somatic ratio (RGS)
Three ovigerous females were collected during our study. An ovigerous female was obtained at the Lma3 station during the first countryside, it has a size (LT) of approximately 52 mm and it weighs (W) 1,79g and has an absolute fruitfulness of 39 eggs. The two other ovigerous females were recorded at the Lma3 station during the PSS (Table V).One has a size of appro ximately 50.38mm, it weighs 0.176g and carries 39 eggs, the other as for it weight of 0.312g, it has a size of 64.18mm and its absolute fruitfulness is of 100 eggs. Average absolute fruitfu lness at this species is of 59 eggs. Relative fruitfu lness as for it varied fro m 22 eggs/g for the female which measures 52 mm (Lma3-GSS 2017) to 34 eggs/G for the largest female wh ich measures 64.18 mm, giv ing an average of 28 eggs/g. The eggs carried by the females are of yello w co lor orange sharp. Concerning the report/ratio gonado-somatic (RGS), it varied fro m 4. 44% for the female collected in first countryside (GSS 2017) to 12.35% for the female collected during the third countryside with an average value is 9.11%. The GSI showed highest percentage of mature females (<50%) fro m January 2017 to February 2018. Maxima of GSI (10.52%) were recorded at PSS (Ju ly) and minim of GSI (1.73%) were recorded during the GSS 2017 (January). The GSI mean is 7.67% in PSS. This indicates that M. macrobrachion in Lep massoun River underwent a reproductive period during the dry season.

Relati onshi p between the number of eggs and morphological parameters at Macrobrachium dux
In our zone of study the coefficient of correlation (R2) are respectively 0.42;0.99 and 0.96 for the relat ion which exists between the number of egg and the length of the carapace (Lc) (Figure 2a), then the number of eggs and overall length (Lt ) (Figure 2b) and finally the nu mber of egg and weight (w) (Figure 2c).The greatest constant of regression (a = 42.59) is observed in the existing relat ion between number of egg and Pt, fo llo w-up of that putting forward the number of eggs and Lt (a = 4.64) and finally that connecting the number of eggs and Lc (a=0.0334). As regards the coefficient of regression (b), it is negative for the existing relat ion between a number of eggs and Pt (b = -28.05) and between the number of eggs and Lt (b=-198.55).This coefficient (b) is positive for the existing relation between the nu mber of eggs and Lc. We note that when the female is large it produces more eggs to its advantage.  (Ouhmidou and al., 2014).The range of the values obtained is located in the range of the temperature of bearable water by the fresh water shrimps which support some until 34 o C beyond which they are vulnerable (Griessinger and al., 1990).
The low values of conductivity (34.6 mg/l) obtained during our study in our rivers would be explained by nature slightly anthropized of our various areas catchment and with the nature of the grounds. These results approaches those obtained by Ajeagah and Al, 2017 in the river Matourou of the catchment area of Nyong (25,89 mg/l).The strong value recorded during the PSP means that there exists in this month a great concentration of dissolved electrolysable salts which is explained by the scarcity of the rains.The brutal fall of conductivity during the great season rain is due to arrival of the rains leading to the flood. These values of conductivity (< 35mg/l) respect the standards of quality of surface water (A E 1999). Light acidity with a tendency of neutrality recorded in the two rivers could be explained by the presence of the humuses resulting fro m the degradation of the sheets died in our rivers wh ich are under cover vegetal. Welcome (1985) affirms that the forest rivers, with water with hu mic characteristics rich person in substance, are slightly with strongly acid with a pH located between 4 and 7 UC. These forest rivers are favorable to the development of the watery organizations. According to (AE 1999), the pH ranging between 6.0 and 8.5 UC is favorable to the expression of the biological potentials of many groups.The low values of my study recorded in the two rivers approaches those recorded by Ajeagah and Al, 2017 in the same ecological area. These results could be explained by the fact that water of the river Lep massoun and Ondomedza is slightly charged. The values of turbidity (< 35, g/l) recorded are relatively low and testify to a good ecological quality accord ing to (MEDD and AE 2003). The differences between the campaigns mentioned by the test of U of Mann Withney could be explained by the fact that during the season of rains the particles are suspended thus affecting turbidity.The average values of color observed in our rivers could be explained by the presence of the colloidal particles of negative charge, these result approach work of (Ajeagah, Yogback et al. 2017) carried out in the catchment area of Nyong. Generally, the average values of dissolved oxygen recorded in our different river make it possible to qualify their water of passable with good (Villeneuve, Legare et al. 2006). These oxygen values which we obtained are inferiors with that obtained by Agadjihouede, 2006 in the lagoon of large-popo (9.76mg/l) but are acceptable for a good growth of the shrimps (Griessinger, Lacroix et al. 1991) for these authors, with the tops of 5 mg/l, the shrimp is under favorable conditions of breeding. With the lower parts of 2 mg/l, the shrimps cannot balance their needs anymore and die when this content persists. The orthophosphate contents recorded in the river Lep massoun are relatively weak and significantly varied fro m one season to another according to the test of Kruskal Wallis (p<0,05).The strong values recorded during the first countryside which corresponds to the great season dries 2017 could be due to the strong mineralizat ion of the organic matter. During this season the river has undergoes a very significant stress hydrous which caused the accumulat ion of the organic matter (sheets dead) as our rivers are under wood what supports a very thorough mineralisation of the organic matter. The NH4 + having increased station Lma1and the Lma3 station in the river Lep massoun is nevertheless below the standards recommended by the (SEQ-EA U, M EDD et al. 2013) ( Table V).Th is would be in relat ion to the bacterial deco mposition of the nitrogenized organic matter of made light reductions in the contents of O2 dissolved recorded in these periods. Their weak presence in the river Lep massoun and Ondoamedza could be explained by made that th e med iu m is sufficiently o xygenated. For this purpose (IBGE 2005) stress that it is in absence of o xygen that the anaerobic bacteria transform nitrates and produce ammon ia (NH3) or ammoniu m (NH4 +) .The strong values of nitrate recorded in the river Ondoamedza during the small season of rain could be exp lained by the scru bbing of the agricultural grounds in the catchment area. Liechti, 2010 underline on this subject which if the contents nitrates exceed 1.5 mg/ L, there probably was arab le land scrubbing.

Biological variables
During this study the inventory of shrimps of the genus Macrobrachium ma de it possible to put forward 14 shrimp species. This specific richness is higher than that obtained by (Tchakonte , Ajeagah et al. 2014) in the river Nsapè in zone périurban of Douala and no species of Macrobrachium is common for us. Our specific richness is also high than that obtain by Makoumbou and al., 2015 in the rivers Lokoundje, Kienke and Lobe Rivers of South Region, Cameroon where we have two species (Macrobrachiu m macrobrachiu m and Macrobrachiu m dux).This d ifference could be explained by the fact Nsapè , Lokoundje, Kien ke and Lobe river are a coastal river and cuts the throat of the coastal species and the land species. Of share the position péri urban, the court of water Nsapé could start to be subject to the influence of the urban activities contrary to our rivers which are located in rural zone where the anthropic activity is quasi null. It is also necessary to note that specific richness of each one of our rivers is higher than that of (Ajeagah, Yogback et al. 2017)in the river Matourou where only one species of Macrobrachium was obtained. This difference would be explained since our rivers are rich in microhabitats contrary to river Matourou. Our specific richness is higher than the specific richness of the genus Macrobrachium (6 species) obtained by (Konan 2009) in seven rivers in Ivory Coast, it is also higher than that obtained in Ivory Coast in the Boubo river (N'zi, B.G. et al. 2008) where nine shrimp species identified and also higher than that is obtained by (Djiriéoulou Kémo madjèh i, Bamba et al.

2017.) in the Forest of the Tanoé-Ehy Marshes in Ivory
Coast. This specific d ifference is exp lained by the methods of fishing used, the types of sampled habitats and the periods of sampling. Seasonal of the specific richness showed that greater specific richness was recorded for the period of rising. These data show that the liv ing conditions are more favorable for the watery organizations during this period (Djiriéoulou Kémo madjèh i, Bamba et al. 2017.).In our site of study, Macrobrachium macrobrachion (10,61%) is not dominating as in work of (Agadjihouede 2006) in the lagoon of large-popo with a percentage higher than our (51%), but this p redominance is not observed by (N'zi this fruitfu lness is also less than that found by Kouton (2004) in the valley of Ouémé, by Goore Bi (1998) in the basin of Bia in Côte.d'ivoire and by Agadjihouede, 2006 in the lagoon of Large the popo for the species Macrobrachium macrobrachion. The weak production of eggs by our females compared to the others species could due to the fact that our rivers are less favorable to the develop ment of this species (low depth, raised color, temperature, average oxygenation) co mpared to the other rivers referred to above. The differences observed could also be allotted to the differences in egg dimension (Beacham and Murray, 1993), the techniques of sampling and the overall length of the female (Deeka and aowei, 2010). In addition, the variations found for fruit fulness can also be due to the differences of environmental conditions, the provisioning food, the seasons and the physiological parameters of environ ment (Bagenal, 1978)  . It was explained that in the genus Macrobrachium, fruit fulness is associated extremely with the female age, and that it can increase while the female becomes ripe (Graziani and Al, 1993) and the size of eggs. The high average value of RGS (11.44) obtained to the PSS could be exp lained by the fact that for this period the ovaries of the individuals females reached a state of more thorough advance compared to the female collected during the GSS 2017 having a smaller index RGS (4.44). Kingdom and Erondu (2013) underline for this purpose that when index RGS lies between 10.55 and 15.57, the fresh water shrimps enter an intense phase of activity of reproduction. This is corroboration by the presence of the ovigerous females with the PSS, corresponding to the period of laying which takes place fro m July to December (Villé, 1972). It should be noted that the presence of the ovigerous females during the GSS 2017 which corresponds to the period of low water level could be explained by a new period of reproduction thus knowing that the reproduction of the genus Macrobrachium is not continuous throughout the year. In our basins slope the Macrobrachium dux reproduces twice a year since production is early and the eggs are rather broad by consequence the larval develop ment is shortened. In this connection Gangbe and al., 2016 stress that reduced fruitfulness is compensated by early fecundation.

V.
CONCLUSION In relation to our work, the diversity and the fertility of shrimps of the genus Macrobrachium in the catchment area of Nyong, we conclude that our various rivers water are of good ecological quality which are slightly acid, fairly o xygenated, slightly mineral-bearing, slightly turbide but with a rather significant color. and Macrobrachium sp9. Macrobrachium macrobrachion is dominate in the river Lep massoun but Macrobrachium sp8 dominates in river Ondoamedza. We note as a whole an equal distribution of the species in the river Lep massoun. They are diversified enough according to the index o f d iversity of Shannon. The équi-partit ion of the species in the river Ondoa medza is higher than river Lep massoun.
Macrobrachium macrobrachion significantly and positively correlated with Macrobrachium sp7. However this species negatively correlated with the the color. The species Macrobrachium sp5 positively correlated with the percntage of saturation out of O2 . As regards Macrobrachium sp7, it has significantly and positively correlated with M ES and alkalinity and finally Macrobrachium sp8 positively correlated with magnesic hardness.
The species Macrobrachium dux, had 3females ovigerous whose settlement is do minated by the females.
The river Lep massoun, the species Macrobrachium macrobrachion enters in intense phase of activity of reproduction during the small dry season but another period of reproduction was observed during the great dry season. In our basins slope the Macrobrachium dux reproduces twice a year since production is early and the eggs are rather broad by consequence the larval development is shortened. The species Macrobrachium macrobrachion is a ubiquist in our t wo rivers, it is it more in the river Lep massoun compared to the other species and average in the river Ondoamedza. For a better knowledge of the reproduction of Macrobrachuim in the forest belt in Cameroon it would be interesting to traverse other aquatic environments.