Fish fauna of Oyun Reservoir, Offa, Nigeria

Heavy metals pollution and it resultant accumulation to toxic levels in the Barekese Reservoir may threaten human health through the consumption of fish from the Reservoir. The presence and concentrations of arsenic and some other heavy metals (Hg, Pb, Ni, Cr, and Cd) were determined in muscle tissues of widely distributed and highly consumed fish species from the Barekese reservoir using Atomic Absorption Spectrophotometry. A total of 45 fish samples comprising three species (Oreochromis niloticus, Tilapia zilli and Heterotis niloticus) were analyzed for their metals levels. Heavy metals concentrations (mg/kg, w.w) recorded showed varying trends of detection among muscle tissues of selected fish species. However, Hg, Ni, Cr and Cd were detected in muscle tissues of all fish species examined in the study. Indices for non-carcinogenic and carcinogenic risks were estimated for children and adult upon their consumption of fish from the Reservoir. Results of the study indicated a significant levels of exposure to Hg, Ni, Cr and Cd through the consumption of fish species from the Reservoir. Health risk assessment also revealed that children are at a relatively higher non-carcinogenic risk through the consumption of metals in Heterotis niloticus whiles the consumption of Cr from all examined fish species from the Reservoir could pose cancer risk health effects to humans with adults being at a higher risk. The present study therefore concludes that anthropogenic activities along the Offin River and within the Reservoir’s catchments are deteriorating the quality of fish from the Reservoir and could pose a significant adverse health risk to consumers.

The fishing gears used in Barra Bonita and Bariri reservoirs, Middle Tietê River, were evaluated in order to provide objective information to assess the need for a revision of the legal framework governing this activity. Monitoring of the fishery production was carried out in the main fishing nuclei, collecting data about the catch composition (number and biomass), selectivity of fishing gear and the by-catch. Information about the predominant fishing arts, catch per effort unit and seasonality of fish production, as well as environmental information, were also obtained. Monthly field campaigns for sampling were done, when the researchers followed the fishing activity, making a detailed record of the catches and the employed fishing gears. It was found that gill net is the least selective among the four modalities practiced, but it is the only one which has legal support. Higher selective fishing gears, such as trawls, cast nets and fishing beat, act mainly on tilapia, a non-native species whose exploitation could be considered beneficial to the conservation of the native fish populations through the reduction of the interspecific competition for resources. Thus it is suggested the restriction of the use of less selective fishing equipment and the liberation of fishing gear that targets the non-native species of cichlids, aiming to reduce the fishing pressure on indigenous species.

Low-head dam impoundments modify local habitat and alter fish assemblages; however, to our knowledge, the pattern of how fish assemblages in the impoundments relate to local habitat, tributary position, and dam characteristics is still unclear. We used data collected in 62 impoundments created by low-head dams in headwater streams of the Qingyi River, China, to examine relationships between fish assemblages and local habitat, tributary position, and dam characteristics. We also assessed the relative importance of the three groups of factors in determining fish species richness and composition. Linear regression models showed that fish species richness was related to substrate heterogeneity, confluence link, and dam number upstream. Redundancy analysis showed that fish species compositions were influenced by substrate heterogeneity, confluence link, dam height, dam numbers upstream and downstream. Overall, dam characteristics were more important in affecting fish species richness but less important in determining fish species composition than local habitat (i.e., substrate heterogeneity) and tributary position. Our results suggest that low-head dam may affect fish species richness in impoundments by modifying local habitat and constraining fish movement, and the relative abundances of those fish species may depend more on species habitat presences and stream size than on impoundment size and number.

Parasites of landed fish from the Great Kwa River, Calabar, Cross River State, Nigeria were studied. Parasitological examination of 180 fish samples belonging to 9 taxa from the River showed 50% incidence for Chrysicthys nigrodigitatus, 16.67% for Heterotis noloticus, Clarias gariepinus and Tilapia galileaus respectively and 0% for Hepsetus odoe, Arius gigas, Momyrus rume, Ethmalosa fimbriata and Cynoglossus senegalensis. Parasite infestations were found in the stomach and intestine, and no parasites were found on the fins, skin and gills. Nematodes, cestodes and protozoan were found in decreasing order of abundance. Diphyllobothrium sp. was found in the intestine of C. nigrodigitatus; Camallanussp. was found in the intestine of H. niloticus and T. galileaus while protozoan cysts were found in the intestine of C. garipinus. Parasites were more prevalent in the fish of 30 to 39.9 cm total length size range. The study determined that in the Great Kwa River the preferred organs of parasites were the intestines and stomach. Key words: Parasites, landed fish, Great Kwa River.

The aim of this study was to determine fi sh capture and composition using gill nets in various of shortening nets, as well as to obtained a suitable size of shortening nets which better productive and sustainable. The study was conducted by fi shing using gill nets 4 sheets, using gill net with mesh size of 2-inch eye openings and various shortening nets, namely 40%, 50%, 60%, and 70%. The setting gill nets were done in the afternoon and hauling the following morning day. Gill net setting were done once a week in September-October 2013. All species of fi sh gilled were collected, then measured the length and weight, as well as on the abdomen was dissected to determine sex. Data on the number and weight of the catch were analyzed descriptively, analyzed using a completely randomized design were subjected to determine the best catches statistically. The results showed that the number of individuals fi sh and the mean weight of fi sh captured in shortening 40%, 50%, 60% and 70% were not signifi cantly different. The most number of fi sh captured was in the nets with shortening of 60%, ie 392.69 (g/ trip), then on shortening of 40%, ie 333.3 g / trip, next on the shortening of 50% as much as 285.9 g/trip and the least in shortening 70% as much as 263.6 g trip. Based on the fi sh species composition, the most dominant of fi sh captured was red devil (52.5%), then tilapia mossambique (27.1%), black tilapia (17.5%), managuin (1.3%), marbel gobby (0.8%), the remaining was consisted of snake head and javain carp (0.8%). Based on sex proportion, the proportion of male fi sh in tilapia mossambique was 63.8%, black tilapia was 53.7%, and red devil was 58.2%, while the remaining was balance between male and female.

The abundance and distribution of fish species in River Orogodo were studied. Sampling was conducted in three stations of the river, from January 2006 to December 2007. The river was demarcated in accordance with local hydrographic conditions as well as intensity of anthropogenic activities along the stretch. Thirty seven species of fish belonging to 20 families and 28 genera were recorded. Cichlidae, clariidae and bagridae dominated the catch by the species; Chromidotilapia guentheri, Hemichromis fasciatus,, Clarias gariepinus,, Auchenoglanis biscutatus and A. occidentalis. The species richness and general diversity were slightly depleted in the mid-stream station (station II) compared to the up- and downstream stations. This probably resulted from the high anthropogenic activities and the resultant effects on key physico-chemical parameters in stations II. The ichthyofauna of River Orogodo was compared with other rivers in the Niger delta and elsewhere in the West African sub-region. The need to reduce the effects of anthropogenic pressure on aquatic resources was recommended. Keywords : Fish, Communities, distribution, abundance, River Orogodo

The fish catches of three upland reservoirs, namely, Kotmale, Victoria and Randenigala reservoirs, were studied for periods of 8, 18 and 9 months, respectively. Tilapia species formed 60-70 % of the catch of all three Reservoirs. Three species of tilapia, namely, Oreochromis mossambicus, O. niloticus and Tilapia rendalli were present in Victoria and Randenigala reservoirs but the last species was not caught in Kotmale reservoir. The three species formed, respectively, 50.8 %. 49.2 % and 0 % of the tilapia catch of Kotmale reservoir, 71.5% 26.6% and 1.9% of that of Victoria reservoir and 96.2%, 2.6% and 1.2% of that of Randenigala ; reservoir . The relative abundance of the three species in the three reservoirs is discussed in relation to that of the three species in other reservoirs in Sri Lanka.

Fish assemblage structures of Badagry creek, Nigeria in relation to abiotic (physical and chemical) variables were studied for 2 years period (November, 2011 – September, 2013). Environmental parameters were monitored in sampling stations randomly selected in each of the three zones established in the creek (3 stations per zone). Fishermen catches were monitored in three major landing sites around the creek (one site per zone). The physico-chemical parameters investigated were within the tolerance limits for aquatic life. Conductance, Salinity and Water depth data showed significant differences (p 0.05) in physicochemical parameters measured seasonally. The survey of fish in the Badagry creek recorded more estuarine and near-shore marine species with a total of 4,045 fish individuals comprising 36 species from 22 families. Dominant fishes included Tilapia zillii (15.2%), Chrysichthys nigrodigitatus (11.3%) and Ethmalosa fimbriata (11.2%). Fish diversity indices in dry season were higher than wet season. Water depth was found to be the most important abiotic factor determining the abundance of species ecological categories. The other abiotic factors tested also showed some influence on the species (ecological categories) abundance, suggesting the importance of environmental parameters in determining fish distribution and abundance.

The kilishi of Heterotis niloticus was produced for determination ofappropriate slurry formulations for fish kilishi preparation. Thirty sixfreshly caught samples of H. niloticus with average weight of 306.20±18.33g,obtained from Kware Lake in Sokoto State were used. Kilishi of this species wasprepared with three different slurry formulations of high (F1), medium (F2) andlow (F3) proportions of groundnut dough to spice mixture in the ratio of1.3:1.0, 1.0:1.2 and 1.0:1.8, respectively. Results of proximate compositionindicated that kilishi of the H. niloticus prepared with formulation 3 (F3)recorded significantly higher (p<0.05) protein content (54.22 ± 0.01%) andlower lipid content (8.00 ± 0.00%), despite recording significantly higher(p<0.05) moisture content (9.93 ± 0.07%). Sensory score of kilishi of H.niloticus processed with F3 formulation rated significantly higher (p<0.05)for taste, flavour and general acceptability with mean scores of 5.94 ± 0.21,5.77 ± 0.20 and 5.50 ± 0.22, respectively. It could be concluded that kilishiof H. niloticus prepared with F3 formulation was the most acceptable hence,recommended for use in kilishi production

Habitat structure is known to influence the abundance of fishes on temperate reefs. Biotic interactions play a major role in determining the distribution and abundance of species. The significance of these forces in affecting the abundance of fishes may hinge on the presence of organisms that either create or alter habitat. On temperate reefs, for example, macroalgae are considered autogenic ecosystem engineers because they control resource availability to other species through their physical structure and provide much of the structure used by fish. On both coral and temperate reefs, small cryptic reef fishes may comprise up to half of the fish numbers and constitute a diverse community containing many specialized species. Small cryptic fishes (<100 mm total length) may be responsible for the passage of 57% of the energy flow and constitute ca. 35% of the overall reef fish biomass on coral reefs. These benthic fish exploit restricted habitats where food and shelter are obtained in, or in relation to, conditions of substrate complexity and/or restricted living space. A range of mechanisms has been proposed to account for the diversity and the abundance of small fishes: (1) lifehistory strategies that promote short generation times, (2) habitat associations and behaviour that reduce predation and (3) resource partitioning that allows small species to coexist with larger competitors. Despite their abundance and potential importance within reef systems, little is known of the community ecology of cryptic fishes. Specifically on habitat associations many theories suggested a not clear direction on this subject. My research contributes to the development of marine fish ecology by addressing the effects of habitat characteristics upon distribution of cryptobenthic fish assemblages. My focus was on the important shallow, coastal ecosystems that often serve as nursery habitat for many fish and where different type of habitat is likely to both play important roles in organism distribution and survival. My research included three related studies: (1) identification of structuring forces on cryptic fish assemblages, such as physical and biological forcing; (2) macroalgae as potential tools for cryptic fish and identification of different habitat feature that could explain cryptic fish assemblages distribution; (3) canopy formers loss: consequences on cryptic fish and relationship with benthos modifications. I found that: (1) cryptic fish assemblages differ between landward and seaward sides of coastal breakwaters in Adriatic Sea. These differences are explained by 50% of the habitat characteristics on two sides, mainly due to presence of the Codium fragile, sand and oyster assemblages. Microhabitat structure influence cryptic fish assemblages. (2) Different habitat support different cryptic fish assemblages. High heterogeneity on benthic assemblages reflect different fish assemblages. Biogenic components that explain different and diverse cryptic fish assemblages are: anemonia bed, mussel bed, macroalgal stands and Cystoseira barbata, as canopy formers. (3) Canopy forming loss is not relevant in structuring directly cryptic fish assemblages. A removal of canopy forming algae did not affect the structure of cryptic fish assemblages. Canopy formers algae on Conero cliff, does not seem to act as structuring force, probably due to its regressive status. In conclusion, cryptic fish have been shown to have species-specific associations with habitat features relating to the biological and non biological components afforded by fish. Canopy formers algae do not explain cryptic fish assemblages distribution and the results of this study and information from the literature (both from the Mediterranean Sea and elsewhere) show that there are no univocal responses of fish assemblages. Further exanimations on an non regressive status of Cystoseira canopy habitat are needed to define and evaluate the relationship between canopy formers and fish on Mediterranean sea.

A study on biodiversity, abundance and distribution was carried out in Onitsha Axis of River Niger in Onitsha North and South Local Government Area, Anambra State, Nigeria for a period of three months. The area was partitioned into Station I (Emejuru), Station II (Bridge Head) and Station III (Akpaka). Fish samples were collected weekly from July to September, 2019 with the aid of fisher folks using gill nets, cast nets, hook and lines and local traps. The results showed a total composition of 4,645 individuals belonging to 15 families and 31 species. Momyridae showed significance (p&lt;0.05) species diversity with seven (7), followed by Bagridae (5) spp. with the remaining 13 families having one and two spp. Station III Akpaka recorded the highest fish diversity of 37%, followed by Station I Emejuru 34% and Station II Bridge head 29%. In terms of species abundance, Bagrus bayad 13.9% &gt;bagrus docmak 8.8% &gt;Chryschythys Nigrodigitatus7.2% &gt;Bargus filamentous 4.5% &gt;Malapters electricus 4.4% &gt;Heterotis niloticus 4.0% &gt;Orochromis niloticus 3.8% &gt;Mormyrus macrophatalmus 3.3%) recorded the highest, followed by Heterobranchus bidorsalis, Mormyrus rume, Mormyrus tarpirus, Mormyrus senegalensis, Schibe mystus Synodontis clarias and Cithrinus citharus had 2.2%, 2.3%, 3.0%, 1.7%, 2.9%, 1.6% and 3.2% respectively, and Hypothermirus pissitacus the least with 0.4%. This research shows that the Onitsha axis of the River Niger is still rich in fish species diversity and abundance; hence concerted efforts should be made by the various government agencies to see that laws guiding the proper use of water bodies are enforced in the Onitsha axis of the River Niger, to enhance economics, conservation and sustainability.

Diving into the deep-end: investigating tropical deep-reef fish assemblages

In order to test the suitability of underwater visual census method in freshwater basins, it was applied and compared with standard sampling methods - gill nets, as well as questionnaires concerning the fish fauna's composition in Stoikovtsi dam (SW Bulgaria). The number of registered species per method was established as: questionnaires &gt; underwater counting &gt; gill nets. The reliability of questionnaires is uncontrolled, whereas underwater counting is nature friendly and permits the calculation of standard values as specimens per unit area, in addition to gill nets, where only CPUE can be estimated. Habitat preference and other specific features can be established, in addition to classical methods (gill nets). The major limitations of underwater counts in fresh waters are turbidity and the diver's experience.

Fluctuations in the abundance and species composition of fishes in the coastal waters of Geumo-do, Yeosu, Jeollanam-do, Korea were investigated from 2002 to 2005. A gill net with entrances on both sides was used to collect a total of 469 individuals (55,180 g) of 3 orders, 18 families, and 28 specie...

During two cruise legs with the RV Victor Hensen (December 1993, February 1994), the demersal fish assemblages of the Golfo de Nicoya (GN), Bahía Coronado-Sierpe Terraba (ST) and Golfo Dulce (GD) areas were assessed from nearshore (approximately 20 m) to shelf edge (approximately 200 m) waters. 44 Beam- and 29 otter trawl collections were made on an area of 2,119,405 m2, yielding a total of 242 species of fish. Despite the lower number of samples taken, more species were collected by the otter trawl (189 compared to 160), due to a wider area swept. As revealed by the species-area curve and a longnormal-curve constructed from the pooled (log) abundance data, the fish assemblage appeared as well sampled and a theoretical species richness (SR) of-306 was estimated for the whole area. Mean species number per collection and mean biomass per area were much lower in the GD-area (9.3 species, 0.36 g/m2) compared to the ST (15.4, 0.81 g/m2) and GN (17.3, 0.74 g/m2) areas, indicating a depauperate fish assemblage in the former. Lowest species numbers and biomass were found in the central deep part of GD with increasing values towards the sill area at the opening of the gulf and towards the shallow stations above the thermocline. Average biomass was an order of magnitude higher in the interior part of GN compared to the other areas with values up to 18.1 g/m2. Based on results of a multivariate analysis of the collections, the GN area can be divided into (1) an interior shallow area above the thermocline (< 50 m) characterized by scianids, sea carfishes, stingrays, flatfishes, sea robins, (2) an outer part (> 100 m) characterized by cods, scorpionfishes, gobies, cutlassfishes, serranids, anglerfishes and flatfishes and (3) a transition zone of the central and lateral parts with a mixed species assemblage with carangids, pufferfish, snappers, several flatfish species and the lizardfish as common elements. Characteristic for the deep basin of GD were small species of the genera Cynoscion and Porichthys. These occurred in low densities, suggesting a reduced carrying capacity of this deep basin for fish biomass in terms of food and oxygen. Species occurring at the shallow stations of GD are also found at a similar depth in the other areas, but many species are missing, namely ariids and many scianids found in the GN area. The species assemblage of the ST area resembles that of GN. Ariids, however, are missing here too. Biotic station parameters like species richness, biomass, abundance and production were not significantly correlated with abiotic parameters (temperature, oxygen, nutrients) suggesting that other habitat factors not evaluated in this study like habitat heterogeneity, distance to the open ocean, current regime and food availability probably are important factors for the structure of the fish assemblage.