Comparative Study of Length-Weight-Relationship (LWR) of the Fishes and Fishing Gears Use in Goronyo Reservoir and River Rima in Sokoto State, Nigeria

Introduction

Stock assessment is a fundamental and important tool needed for generating inputs necessary in developing strategies for efficient and proper management, development and enhancement of the fish species in any water body [1, 2]. The length-weight-relationship (LWR), length-length- relationship (LLR), weight-w eight-relationship (WWR) and Fulton’s condition factor (‘k’) are some examples of stock assessment tools use in fisheries management. These tools can be used to predict the health status, standing crop or biomass, growth pattern and yield of fish stock. Length-weight data of population are basic parameters for any monitoring study of fishes since it provides important information concerning the structure and function of populations [3]. In fish population studies, it is therefore imperative to study fish species diversity together with the fish stock assessments in order to have a clear understanding of the management strategies peculiar to the fish population in such a water body.

According to Ita [4], fishery management is water body specific. Fish growth is an addition in length and size as it ages with a growth pattern of either isometric or allometric [5]. The isometric growth pattern was when a fish shape did not change when growing up, while in an allometric pattern of growth, the fish either becomes slender as it grows or becomes deeper and bulkier.

Various scholarly works were published which reported and described different means values for LWR, LLR, CF et cetera, for many important freshwater fish species [2, 6, 7, 8, 9, 10, 11, 12]. There was a paucity of information regarding fish LWR and fishing gears used in the Goronyo reservoir and downstream River Rima [13]. Thus, this study was aimed at bridging the gap and therefore provide information on LWR of some important fish species and the fishing gears used by the artisanal fishermen in the two water bodies.

Discussion

The results showed most of the fish to be fairly exhibiting allometric growth patterns in both water bodies. For instance, the species Latesniloticus exhibited positive allometric growth pattern. This means as the fish were growing; they were adding weight and becoming bulkier and deeper. The same thing happened with other predators in both water bodies, such asBagrusdocmac, Bagrusbayadmacropterus, Auchenoglanisoccidentalis and Hydrocinusforskalii.

The results obtained were probably due to good/ favourableaquatic environments, slightly better in river Rima as reported by Malami and Magawata [13] and Abubakar, et al. [22]. While some of our results are in agreement with other regionaland international findings on biometrics of fish studied, others are contrary. Similar results were obtained in the studies conducted by Mansor, et al. [10] in Kerian river basin and Keru Lake all in Malaysia. Furthermore, the current study was in conformity with the positive allometric growthreported by Froese [9] among 1773 specimens of fish.

Several studies corroborate the negative allometric growthreported in our study. According to Reed, et al. [23], Bagrusfilamentosus, Auchenoglanisbiscutatus and Claroteslaticep were relatively insectivorous or carnivores in feeding habits. These species exhibited negative allometric growth patterns from both water bodies. This could be due to steep competition from other species of the same families who are favorably disposed in the Rima and the reservoir. Imaobong, et al. [24] also reported steep competition for food among species of same families in Qua Iboe River estuary, AkwaIbom State, southeastern Nigeria. This could probably be responsible for them exhibiting negative growth pattern in the two water bodies. Correspondingly, Waidi [25] reported negative allometric growth patterns (b = 2.114) for an African silver fish, Chrysichthysnigrodigitatus in Ogun State coastal estuary.

Synodontisclarias and others from Mochokidae family exhibited positive allometric growth patterns more than the Synodontisgobroni in the Rima which exhibited negative growth patterns. This finding was also reported by Beniditto- cecillio, et al. [6] in Itaipu reservoir, Parana, Brazil where the authors observed mean b values ranged from 2.34 to 3.35 for about 72 fish species. Clariasgariepinus exhibited positive allometric growth pattern in both Goronyo and River Rima more than Clariasanguillaris which might be related to their feeding habits and reproductive strategy [26]. Mormyrusrume which accounted for the highest individuals caught exhibited positive allometric growth pattern for most of the 134 specimens examined. However, Mormyropstapirus exhibited negative allometric growth pattern (b+ 2.3) and was only found in Rima. By adapting to bottom-feeding habit, this species successfully colonized the bottom strata as was reported by Reed, et al. [23] in the northern Nigerian water bodies. The fishermen successfully caught these species using Ndrutu and other traps and bottom gill nets in the two water bodies. Similar findings were reported by Reed, et al. [23] and Ita [4] in northern Nigeria.

Oreochromisniloticus exhibited a positive allometric growth pattern in both Goronyo and the Rima, indicating the adaptability of the species in the reservoir. But Hemichromisfasciatus was not found in the reservoir and had exhibited a negative growth pattern in the Rima. According to Reed, et al. [23], Hemichromisfasciatus is a predatory Cichlid and probably could not survive the steep competition for food with the other predators in the reservoir. Nehemiah, et al. [2] reported both positive and negative allometric growth patterns in Tilapia zilli and some Oreochromisniloticus species cultured in freshwater and seawater ponds in Tanzania. But Dan-kishiya [11] reported mean negative allometric growth patterns for 5 tropical fish species which included Tilapia zilli, Tilapia mariae and Oreochromisniloticus in a tropical reservoir in Abuja. Labeocoubie and Labeosenegalensis, a very important fish species exhibited positive growth pattern in River Rima and were completely absent in the reservoir. This indicated the species to be suitable in lotic rather than lacustrine aquatic environment of the reservoir. Ita [4] also reported the high number of this specie in river Niger prior to creating of Lake Kainji. Distichodusrostratus and Distichodusbiscutatus all exhibited negative (2.8 and 2.7) allometric growth patterns in the reservoir. The reservoir had scanty macrophytes and other vegetation probably was responsible for the absence of these species. Reed, et al. [23] reported that this species lived on grasses and therefore could not thrive well in open water devoid of vegetation cover.

The agreements and disagreements with other works could be attributed tothe condition of the species itself, its phenotype and its specificgeographic location and hence its environment as several researchers have observed [27]. Phenotypic factors can play a role in affectingthe allometric growth data. The bodyform and shape strongly affect the LWRs [28]. The variation in the obtainedbvalues might be correlated with many factors such as food availability, season and sex [29, 30].

Survey on the fishing gears and equipment has shown that gillnets, hook and lines, and Malian traps are the most important fishing gears in both Goronyo and river Rima. Similar findings were reported by Reed, et al. [23] in Northern Nigeria and Gusau, et al. [21] in the Bakolori reservoir. Most of the fishing gears are seasonal and selective and is based on the type of fish species to be catch.The types of fishing gears (gillnet, cast net, hook and line, and Malian trap) found in this area were also reported by Adeyemi, et al. [31] as the common fishing gears infish gear survey of Gbedikere Lake, Bassa, Kogi State, Nigeria.

Conclusion

This study revealed that most of the predatory fish species in both river Rima and Goronyo reservoir exhibited positive growth patterns, indicating the ability to adapt and colonize the different ecological niche in the water bodies. But few species with low resilience and ability to compete for food and space became slender as they were aging. The study recommended paying attention to Labeocoubie in the river Rima because of its ability to survive expected predation as they were growing. It’s also very important for the gears to be regulated in order to protect the fishes in the two water bodies from been overfished.

Acknowledgment

The authors wish to acknowledge the support and encouragement of the management of the Sokoto-Rima Basin Development Authority for making their facilities available to us. We also wish to thank the fishermen who took part in the fishing gears and equipment survey as well those whose fishes were made available to us for stock assessment.