Journal of Fisheries & Livestock Production
Open Access

Ichthyodiversity refers to variety of fish species depending on the context and scale; it could refer to alleles or genotypes within piscian class to the species [1]. Fishes are the important elements in the economy of many nations as they have been a stable item in the diet of many people. These fish resources, apart from being a major source of high quality animal protein for man, it also provides several socioeconomic values as source of job opportunities and raw material for some industrial activities as well as recreational purposes [2]. Inland waters biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms; and are estimated to cover at least 14 million hectares [3] which are being fished by artisanal fishermen. Their conservation and management are critical to the interests of all human, nations and governments.

According to Ehrlich and Willson [4] the study of these biodiversity is essential for stabilization of ecosystem, protection of overall environmental quality for understanding intrinsic worth of all species on the earth. Biodiversity is the quantity, variety and distribution across biological scales ranging through genetics and life forms of populations, species, communities and ecosystems [5]. It is often used as a measure of the health status of the biological system. The streams and rivers are facing number of environmental problems throughout the world largely associated with anthropogenic activities in their catchment areas [6]. Also, habitat loss and environmental degradation causes rapid decline in biological diversity which is a critical challenge for the modern era [7]. Freshwater biodiversity is now in a state of crisis, a consequence of decades of human exploiting rivers with over fishing, pollution and development activities and Lake Geriyo, Adamawa state is not exempted from this crisis.

Lake Geriyo is one the man-made lake in Adamawa state Nigeria, originally formed as a flood plain area as a result of yearly over-flooding from the Upper Benue River. This Lake is also used for FADAMA farm irrigation purpose during the dry season. River conservation and management activities in most countries suffer from an inadequate knowledge of its biota constituents, especially in large, poorly investigated tropical river systems in Asian and African [8,9], tropical Australian [10] and Amazon regions [11]. The diversity of many water bodies have been investigated by different researchers which include Adeyemi et al. [12] on Gbedikere lake, Bassa, Kogi state; Lawson and Olusanya [13] on three tributaries of River Ore, Southwest, Nigeria; Ipinmoroti [14] on Asejire Lake; Dan-Kishiya et al. [15] on lower Usuma reservoir in Bwari; Adaka et al. [16] on Oramiri-Ukwa river, Southeast Nigeria, Abuja; Ekudayo et al. [17]on lake Geriyo, Adamawa state among others.

As Conservation and management planning begins with a comprehensive assessment of biodiversity which entails life histories, species richness, endemism, rarity, range of morphological and genetic variability, and evolutionary histories but the necessary first step is identification of the organisms [18]. Lake Geriyo, been an important source of livelihood not only to the artisanal fishers but to the community at large. Therefore, there is need for regular assessment of fish diversity, distribution and population towards proper monitoring, management and conservations so as to maintain and sustain the fisheries of this Lake.

Study area: Lake Geriyo is a flood plain lake, located at the outskirt of Jimeta metropolis Adamawa state on the North-East Nigeria. It lies between longitude 12°25’E and latitude 9°8’N (Figure 1). It is a shallow water body with a mean depth of about 2 meters and the mean annual rainfall of is between 900 and 1100 mm with the rainy season ranging from 150 to 160 days, usually from May to October. Temperature ranges from 20°C in December to January and intense heat with temperatures of 30°C to 42°C in March to April. It experiences some influx of waters from flood during rainy season and overflows from river Benue which serves as a major water source to the lake. The study region area is about 1,548 km².

Figure 1: Map of lake Geriyo.

a) Collection of samples: Samples were collected once in a week from the landing site for the period of six (6) months, which extended from July to November, 2015. Fish species were caught with the assistance of local artisanal fishers using different types of nets namely: gill nets, cast nets, hook and line, local traps and bag nets of various sizes. The services of six (6) fishermen were explored during the collection periods. Collected fish samples were taking to the Department of Fisheries laboratory, Modibbo Adama University of Technology, Yola for proper identification. The fish samples were identified using the fish guide to freshwater fishes of Nigeria and field guide to Nigerian freshwater fishes.

Fish species diversity was subjected to diversity analysis using different indices like Shannon-Weiner index (H) [19]; Simpson Dominance index (D) and Simpson index of diversity (1–D) [9] (Figure 2).

Figure 2: Fish species abundant in lake Geriyo from June 2015 to Nov 2015.

b) Shannon-Weiner index: Species diversity was calculated following Shannon-Weiner index (H) which depends on both the number of species present and the abundance of each species

H =ΣPiLog2Pi

where, H=Shannon–Weiner index

Pi=ni/N

where

ni=Number of individuals of each species in the sample

N=Total number of individuals of all species in the sample

c) Simpson’s diversity indices: Simpson’s index (D) is a measure of diversity, which takes into account both species richness, and an evenness of abundance among the species present. In essence it measures the probability that two individuals randomly selected from an area will belong to the same species.

Where,

ni=Number of individuals of each species in the sample

N=Total number of individuals of all species in the sample

The value of D ranges from 0 to 1. With this index, 0 represents infinite diversity and, 1, no diversity. That is, the bigger the value the lower the diversity.

d) Simpson’s index of diversity (1–D). This is a reciprocal of the Simpson’s index of dominance and the value usually ranges between 0 and 1, which indicates that the greater the value, the greater the diversity of the sample area (Figure 3).

Figure 3: Fish abundant based on species in lake Geriyo from June 2015 to Nov 2015.

A total of four thousand, seven hundred and fifty two (4752) individual fish samples were sampled from June to November which belong to eighteen (18) species and fourteen (14) families (Table 1). The lowest samples of fish species was recorded in the month of June while the highest was recorded in the month of November (Table 1). Oreochromis niloticus was the most abundant species during the sampling period which accounted for 1217 individuals and 25.61% of the total sampled species. Sarotherodon galileaus and Clarias gariepinus were next to O. niloticus in abundant with 702 (14.77%) and 634 (13.34%) individuals respectively (Table 1). Gymnarchus niloticus was the least abundant during the sampling period with 58 individuals and this accounted for 1.22% of the total sampled species and this was followed by Lates niloticus, 75 (1.58%) and Hydrocynus forshkalii, 98 (2.06%). The family Cichlidea has the highest composition with the three (3) species (Sarotherodon galileaus, Coptodon zilli and Oreochromis niloticus), followed by the family Mochokidae (Synodontis clarias and Synodontis schall) and Mormyridae (Mormyrus rume and Gnathonemus abadii) with two (2) species each. Fish species abundant by family showed that the family Cichlidae has the highest by number and percentage (2154; 45.33%). This is followed by the family Clarridae (634; 13.34%), Mochokidae (310; 6.52%), Mormyridae (255; 5.45%), Citharinidae (242; 5.09%) and Protopteridae (198; 4.17%). The least fish species abundant by family was found in the family Gymnarchidae (58; 1.22%) and followed by the family Centropomidae (75; 1.58%) and Alestidae (98; 2.06%) (Figure 4).

Table 1: The composition, abundance and diversity of fish species sampled from lake Geriyo.

Figure 4: Fish species abundance by family in lake Geriyo from June 2015 to Nov 2015.

It was observed from the result that the month of June recorded the least number of fish sampled (763 fish individuals) while November had the highest with 835 fish individuals.

The diversity indices of the studied area showed a Shannon-Weiner (H) value of 2.483 while the Simpson’s Dominant (D) and Simpson’s index (1-D) were 0.1211 and 0.8789, respectively.

The Fish species composition of Lake Geriyo revealed a fair higher species diversity of eighteen (18) species from fourteen (14) families compared to eleven (11) species from the three tributaries of River Ore Southwest Nigeria [13], twelve species from Gbedikere lake, Bassa, Kogi State [12] and eleven (11) species from lower Usuma reservoir in Bwari, Abuja [15]. But not as rich in diversity as that Asejire lake, Southwest Nigeria with twenty-seven (27) species [14] and that of Oramiri-Ukwa river, Southeast Nigeria with twenty-five (25) species [16]. The eighteen (18) species recorded in this present study were higher than the 14 species observed by Ekundayo et al. [17] from the same water body. This could be as a result of frequent inflow of water from the Upper Benue River to the Lake which may have periodically introduced new fish species to the lake from time to time. Though, a particular species (Malapterurus electricus) was reported by Ekundayo et al. [17] which was not found in this present study and that could be attributed to the species not susceptible to the gears used as earlier documented by Ipinmoroti [14]. The most abundant species were from the family Cichlidae (O. niloticus and S. galileaus) which were higher in each of the sampling period months. This showed a typical dominance tendency of the tilapiine cichlids in every environment they inhabit. This also follows the trend of results observed by Olawusi- Peters [20] in Agboyin Creek, Lagos State and by Ipinmoroti [14] in Asejire Lake. This could be attributed to the prolific and spontaneous breeding habit of the species from this family. The species from this family are known for their easy widespread even in area where they are not native or historically an important component of the catch [1]. Clarias gariepinus was next in abundant after O. niloticus and S. galileaus which had 13.34% of the total compositions. This was similar to the findings of Adeyemi et al. [12] which recorded 13.16% of the total composition of fish observed in Gbedikere Lake, Bassa, Kogi State. The least composition of Gymnarchus niloticus (1.22%) and Lates niloticus (1.58) observed in this study may be an indication that these two species are threatened in this lake or overfished. Due to their ability to grow big and their high price values, fishers have been known to hunt for them and this could explain why their compositions have reduced over time as documented by Peter et al. [21]. The low quantities of fish recorded in the months of June, July and August could be as a result of high fishing efforts in the Lake during these months while the fishing efforts fairly reduced in the month of October and November as the lake usually exercise partially closed season between November and April [22].

The diversity index, Shannon-Weiner (2.483) indicated a fair fish species diversity in the study area. The diversity using Simpson’s index of Dominance (D) (0.1211), indicated high species diversity as the value usually ranges from 0 to 1 and 0 represent infinite diversity while 1 represent no diversity. That is the larger the value of D the lower the diversity [13].

Also, the Simpson’s index of diversity (0.8789) showed a very fair diversity in the studied area as it usually ranges from 0 to 1 with greater value indicating greater diversity. This index suggests the probability that every two individual fish samples that is randomly selected from the studied area will belong to different species.

This study could serve as awareness in assisting relevant bodies in the management and conservation of fisheries resources of this lake and the nation at large in the need for quick intervention to rescue these threatened fish species. Also, external factors that are known to affect the population of freshwater species which include habitat loss as a result of withdrawal of water for human usage and irrigations should be addressed. Enactment and enforcement of laws and orders by regulating agencies in the management and conservation of the resources of natural waters should be considered a top priority and the partially closed season that is been exercise in this lake should be made complete close season so as to allow the fish species to re-stock themselves.