The state and known impacts of fish species transferred to or within continental Africa

Fish introductions have been made from small fish ponds to the largest lakes in Africa. The primary intent of these introductions has been to sustain or increase fish production, although some introductions have been made to develop sport fisheries and to control unwanted organisms. Some of these introductions have fulfilled their objective in the short term, but several of these "successful" introductions have created uncertainties about their long term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into lakes Victoria and Kyoga in 1950s and early 1960s. By the 1980s O. niloticus and O. niloticus dominated the fisheries of these lakes, virtually eliminating a number of endemic fish species. The loss of genetic diversity of the fish in the worlds second largest lake has also been accompanied by a loss of trophic diversity. The transformation of the fish community has, in Lake Victoria coincided with a profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. In contrast, the introduction of a planktivore, Limnothrissa miodon into Lake Kivu and the Kariba reservoir has established highly successful fisheries with little documented effect on the pre-existing fish community or trophic ecology of the lakes. The highly endemised species-rich African Great lakes may be particularly sensitive to species introductions and require special consideration and caution when introductions are contemplated because species extinctions, introgressive hybridization and ecosystem alterations may occur following fish introductions.

The changing fisheries of Lake Victoria, Uganda

Lake Victoria had a complex multi-species fishery dominated until the late 1970s by the tilapiine and haplochromine cichlids but with important subsidiary fisheries of more than 20 genera of non-cichlid fishes. Since the 1980s, however, the fishery has been dominated by the Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus eduardianus) both introduced into the lake during the late 1950s and early 1960s and Rastrineobola argentea, a pelagic cyprinid. Although the actual landed commercial catch figures from the Uganda sector of the lake point to the increased landings since 1984, the catch rates in the experimental trawl fishery and mean weight of fish in both experimental trawl and commercial fishery have been on the decline.

The impact of exploitation, competition, and predation on the changing stocks of Lake Victoria

The dramatic decline in fish species diversity in Lake Victoria has been attributed to predation by Nile perch, Lates niloticus Linne, without sufficient justification. Exploitation, interspecific competition and hybridization had profound impact on the decline of the indigenous commercial fish species. The roles of exploitation, competition and hybridization, and of predation by the Nile perch on changes in species diversity have been discussed. Lates was largely responsible only for the decline of the haplochromine stocks.

Cast-net fishery on northern portion of Lake Victoria and upper Victoria Nile

This project survey on cost-net was conducted at the Northern portion of Lake Victoria and Upper Victoria Nile. The selected fish -Landing sites, where sampling exercises were carried out include: Loco, Jinja pier (covering Lake Victoria) and Railway bridge, New bridge and Kalange (covering upper Victoria Nile). Research was focused on the cast-net design, target commercial fish stocks, impact of cast-net on the fish stocks, mesh-size and techniques ofcast-netting. The research results show that cast-net fishery destroys fish breeding and nursery grounds and other fish ecosystem. The gear targets Oreochromis niloticus and Occassional by catches e.g. Lates niloticus, Mormyrus Kannume Bagrus docmak and Clarias gariepinus. The multi-panel cast-net of mesh-sizes ranging from i (5lmm) to 6' (152mm) were adaptable by fishermen but they mostly caught immature fish. Nevertheless, this gear showed highest efficiency compared to other gears used at the project area. These research results will be useful to researchers, extension workers and Fishenes, students under taking special research or study on this gear.

Determinação da toxicidade aguda e caracterização de risco ambiental do herbicida Roundup (glifosato) sobre três espécies de peixes

Considering their commercial importance, as these are the species of freshwater fish more commercialized in Brazil, their occurence in different kinds of aquatic environments (lakes, rivers and dams) and for being tolerant to a wide range of variation of various physical parameters and chemical water, the fish species Oreochromis niloticus, Cyprinus carpio and Colossoma macropomum were chosen for this study, furthermore, to test the toxicity we used the herbicide Roundup. The fingerlings of tilapia (Oreochromis niloticus), commun carp (Cyprinus carpio) and tambaqui (Colossoma macropomum) were submitted to the herbicide roundup in the following concentrations: 0.0 (control); 18,06; 19,10; 20,14; 21,18 and 22,22 mg.L-1, 0.0 (control); 13,89; 14,86; 15,83; 16,81 and 17,78 mg.L-1, and 0.0 (control); 18,06; 19,10; 20,14; 21,18 and 22,22 mg.L-1, respectively, three for 96 hours. The LC50 - 96h for O. niloticus, C. carpio and C. macropomum was 21,63, 15,33 and 20,06 mg.L-1 of the herbicide roundup, respectively. The results show that this herbicide is classified as slightly toxic to the three species. The values of dissolved oxygen, pH and temperature recorded in the aquarium control and aquarium experimental of the three fish species have remained without significant variations during the tests, which reduces the possibility of death caused by sudden variations of these parameters during the 96 hours the experiment. The values of LC50 between different species of fish were observed, noting that the species O.niloticus, C. carpio and C. macropomum showed no expressive differences. The values of environmental risk of Roundup were calculated to obtain more stringent parameters in assessing the dangerousness of those on nontargets. The risk of environmental contamination by Roundup for the Nile tilapia, common carp, and tambaqui are low for the lowest application rate (1 L.ha-1) and depths (1.5 and 2.0 m). The dilution of 100%, the highest recommended dose (5 L.ha-1) and depths (1.5 and 2.0 m) the risk is moderate for the three species. The values of the Risk Ratio (QR) were greater than 0,1, indicating that the values of the CAE and LC50 are above acceptable levels and there is a need, this study, a refinement in ecotoxicological tests

An examination of the usefulness of single-species biomass models for the management of Lake Victoria fisheries

Nile perch (Lates niloticus), tilapia (Oreochromis spp), dagaa (Rastrineobola argentea, silver cyprinid), and haplochromines (Tribe Haplochromini) form the backbone of the commercial fishery on Lake Victoria. These fish stocks account for about 70% of the total catch in the three riparian states Uganda, Kenya, and Tanzania. The lake fisheries have been poorly managed, in part due to inadequate scientific analysis and management advice. The overall objective of this project was to model the stocks of the commercial fisheries of Lake Victoria with the view of determining reference points and current stock status. The Schaefer biomass model was fitted to available data for each stock (starting in the 1960s or later) in the form of landings, catch per unit effort, acoustic survey indices, and trawl survey indices. In most cases, the Schaefer model did not fit all data components very well, but attempts were made to find the best model for each stock. When the model was fitted to the Nile perch data starting from 1996, the estimated current biomass is 654 kt (95% CI 466–763); below the optimum of 692 kt and current harvest rate is 38% (33–73%), close to the optimum of 35%. At best, these can be used as tentative guidelines for the management of these fisheries. The results indicate that there have been strong multispecies interactions in the lake ecosystem. The findings from our study can be used as a baseline reference for future studies using more complex models, which could take these multispecies interactions into account.

Diversidade Ictiofaunística e Ecologia reprodutiva de uma espécie nativa de peixe da Bacia Piranhas-Assu, RN

The Caatinga biome is rich in endemic fish species fauna. The present study the results of fish faunal surveys conducted in the hydrographic basin of Piranhas-Assu of the Brazilian Caatinga biome. The fish samples collected were distributed in four orders (Characiformes, Perciformes, Siluriformes and Synbranchiformes), 11 families (Characidae, Curimatidae, Auchenipteridae, Anostomidae, Prochilodontidae, Erythrinidae, Cichlidae, Sciaenidae, Heptapteridae, Loricariidae, Synbranchidae) and 22 species, of which 17 are endemic and five have been introduced from other basins. The order Characiformes was the most representative in number of species (46,35% ) followed by Perciformes (35,38%), Siluriformes (17,44%) and Synbranchiformes (0,5%). The Nile tilapia, Oreochomis niloticus, the only exotic species, was most expressive in number of individuals (24.92%) followed by the native species piau preto, Leporinus piau (18,77 %). Considering the relative frequency of occurrence of the 22 species, 13 were constant, five were accessory and four were occasional. This study investigated the reproductive ecology of an endemic fish black piau, Leporinus piau from the Marechal Dutra reservoir, Acari, Rio Grande do Norte. Samplings were done on a monthly basis from January to December 2009, and a total of 211 specimens were captured. The environmental parameters such as rainfall, temperature, pH, electrical conductivity and dissolved oxygen of water were recorded. The sampled population showed a slight predominance of males (55%), however females were larger and heavier. Both sexes of L. piau showed positive allometric growth, indicating a higher increase of weight than length. The first sexual maturation of males occurred at smaller size, with 16.5 cm in total length than females (20.5 cm). During the reproductive period, the condition factor and gonadosomatic index (GSI) of L. piau were negatively correlated. This species has large oocytes with a high mean fecundity of 54.966 with synchronous oocyte development and total spawning

Mushroom growing as a livelihood option to fishing among Lake Edward fisher communities

Fisheries activities are the main source of livelihood for the communities that live at Lake Edward fish landing sites. The landing sites include: Kazinga, Katwe, Kayanja, Kishenyi Rwenshama and Katunguru and are located within Queen Elizabeth Conservation Area (QECA). In spite of being the main source of livelihood, 74% of the respondents in a 2013 survey reported that catches for the main targeted fish species namely: Bagrus docmak (Semutundu), Oreochromis niloticus (Tilapia) and Protopterus aethiopicus (Mamba) were declining due to overfishing and catching of immature fish by the rapidly increasing population. Lake Edward Frame surveys had shown that the number of fishing crafts increased from 302 in 2008 to 330 in 2011, while the number of fishers increased from 355 to 600 during the same period. Between 2008 and 2010, catch per boat, for Bagrus docmak (Semutundu) declined from 5.25 kg to 4.04 kg and for Protopterus aethiopicus (Mamba) from 2.63 kg to 1.03kg. It has been suggested that reducing pressure on the lake should be handled using different approaches, one of which is introduction of programs for enhancing livelihood options which do not conflict with conservation of Queen Elizabeth Conservation Area (QECA). The main goal of this study was therefore to identify, prioritize and pilot livelihood options at selected landing sites of Lakes Edward and George.

Población anidante e impacto en la pesca artesanal del cormorán neotropical Phalacrocorax brasilianus (Suliformes:Phalacrocoracidae), en el sitio Ramsar Cerrón Grande, El Salvador.

El cormorán neotropical (Phalacrocorax brasilianus) es una especie de ave acuática abundante en los humedales de El Salvador. La depredación de peces que realiza en los ecosistemas acuáticos, está generando un conflicto con los pescadores que asocian la disminución de la pesca con la conducta depredadora del ave. Entre abril de 2010 a febrero de 2011, se realizó una investigación tendiente a conocer el estado de la población de P. brasilianus en el Sitio Ramsar Embalse Cerrón Grande, El Salvador. El estudio se desarrolló por medio de cinco censos y recolecta de ejemplares, estos últimos se utilizaron para analizar el contenido estomacal. El máximo de ejemplares contabilizados fue de 28,063 individuos y 3,000 parejas reproductoras. Se recolectaron 266 ejemplares, de los cuales, 207 contenían peces en sus estómagos,cuyo peso individual varío de 2 a 307 g ±52 g.Se encontró un total de 1,078 ejemplares de peces correspondiente a diez especies, cuatro de ellas obtuvieron los mayores valores de abundancia: bagre (Cathorops steindachneri)con 29%, seguido por guapote (Parachromis managuensis) con 25%, tilapia (Oreochromis niloticus) con 22% y plateada (Astianax aeneus, Roeboides bouchellei) con 21%. ABSTRACT: The neotropical cormorant (Phalacrocorax brasilianus) is a species of waterfowl abundant in the wetlands of El Salvador. Fish predation on aquatic ecosystems is generating a conflict with fishermen that associating declining fishing with predatory behavior of this bird. From April 2010 to February 2011, an investigation was conducted aimed at knowing the state of the population of P. brasilianus in the Ramsar wetland Cerron Grande, El Salvador. The study was conducted through counting and collecting of birds, to analyze the stomachic contents. The maximum recorded was 28.063 individuals and 3,000 breeding pairs. 266 birds were collected, on 207 it found fish in their stomachs, whose individual weight ranged from 2-307 g ± 52 g. A total of 1,078 fish specimens was found, from ten species, four of them obtained the highest values of abundance: bagre (Cathorops steindachneri) with 29%, followed by guapote (Parachromis managuensis) with 25%,tilapia (Oreochromis niloticus) with 22% and plateada (Astyanax aeneus, Roeboides bouchellei) with 31%.

Estratégia alimentar com ciclos de restrição e realimentação no desempenho produtivo de juvenis de tilápia do Nilo da linhagem GIFT

O objetivo deste estudo foi avaliar a ocorrência de resposta compensatória no desempenho produtivo de juvenis de tilápia do Nilo Oreochromis niloticus, linhagem GIFT, submetidos a diferentes estratégias alimentares. Foram utilizados 135 juvenis de tilápia, distribuídos em nove tanques de polietileno de 100L cada. As estratégias testadas foram: grupo controle (alimentado todo dia), grupo alimentado por cinco dias seguidos de dois dias de restrição de alimento (5A/2R) e grupo alimentado por quatro dias seguidos de três dias de restrição de alimento (4A/3R). Foram avaliados parâmetros físico-químicos da água e de desempenho produtivo. Os resultados foram submetidos à análise de variância, e as médias foram comparadas pelo teste Tukey, a 5% de probabilidade. A qualidade de água, o fator de condição e a conversão alimentar não foram influenciados pela estratégia alimentar. O grupo alimentado com a estratégia 5A/2R apresentou peso final, ganho de peso e taxa de crescimento específico semelhantes ao grupo continuamente alimentado (7,8 e 9,2g; 6,4 e 7,8g e 2,7 e 3,0% dia-1, para peso final, ganho de peso e taxa de crescimento especifico, respectivamente). A estratégia 4A/3R apresentou os piores resultados de desempenho produtivo, e a estratégia 5A/2R pode ser usada na alimentação de juvenis de tilápia do Nilo sem prejuízo ao desempenho produtivo, possibilitando inclusive redução de até 22,5% na quantidade de alimento ofertada.

Desenvolvimento de bioblendas poliméricas a partir de gelatina bovina e de tilápia com amido de milho

The natural raw materials acquired special importance beside the mineral raw materials with the need for using alternative sources to oil, because they can be used to produce biopolymers. Gelatin, produced from the denaturation of collagen, and starch, an abundant polysaccharide in various plants, are examples of biopolymers which have several technological applications, especially in films. The objective of this work is to produce polymeric bioblends with gelatin and corn starch using two types of gelatin: commercial bovine gelatin and gelatin produced from mechanically separated flesh of tilapia (Oreochromis niloticus). For the extraction of tilapia gelatin 3 distinct pretreatments, followed by extraction in distilled water under heating were performed. The properties of gelatin extracted were similar to bovine gelatin, and the differences can be explained by the difference in extraction processes and sources. Blends of commercial gelatin and starch were produced in an internal mixer from a Haake torque rheometer, to study the behavior of the gelatin mixture with starch, thus, the same compositions were processed by twin screw extrusion, to define the mixing parameters. Subsequently, the extrusion of blends of tilapia gelatin and corn starch was carried out in the same twin screw extruder. The physico-chemical, rheological and morphological properties of the blends with thermoplastic starch and gelatin were studied. It was found that various properties vary linearly with increasing concentration of the components. The blends produced are immiscible, and among the two gelatins, tilapia gelatin showed a better interfacial adhesion with the corn starch. Regarding the morphology, gelatins formed the dispersed phase in all compositions studied, even in compositions rich in starch. Can be concluded that the procedure for tilapia gelatin extraction is feasible and advantageous, and the increasing in its scale to a reactor of 30 liters is possible, with a satisfactory yield. The bioblends of bovine gelatin/corn starch and tilapia gelatin/corn starch were successfully produced, and the processing conditions were appropriate

Eugenol em juvenis de tilápia do nilo: concentrações e administrações sucessivas

Several anesthetics are used in aquaculture to reduce the stress caused by management. In the field, the most common anesthetic is benzocaine, but several authors are researching about eugenol. The objective of this study were to compare the action of these drugs on the anesthetics stages and measure the effects of successive administration of eugenol on the anesthetics stages in Oreochromis niloticus. In the first test, fish (47.73 +/- 8.73 g and 14.23 +/- 0.81 cm) were subjected to five concentrations of eugenol (40, 60, 80, 100 and 120 mg L-1) and one of benzocaine (100 mg L-1). All the anesthetic concentrations tested were able to induce fish to all stages of anesthesia, and revealed an inverse relationship between the induction times and increased concentrations. The minimum concentration of eugenol to induce anesthesia was 100 mg L-1. In the second test, the juveniles (38.07 +/- 5.00 g and 12.70 +/- 0.54 cm) were exposed to concentrations of 60, 80, 100 mg L-1 of eugenol, as determined in the first test. Evaluating the differences between successive days, there was no significant difference (P > 0.05) between anesthetics stages in the concentrations of eugenol tested, suggesting that the residue of eugenol was removed from the fish in less than 24 hours.

Sex group composition, social interaction, and metabolism in the fish Nile tilapia

O objetivo deste trabalho foi testar se grupos monossexuais de machos gastam mais energia e exibem perfil agonístico diferente de grupos formados por um macho e uma fêmea na tilápia-do-Nilo (Oreochromis niloticus). Tais diferenças são esperadas, pois machos e fêmeas competem por diferentes recursos reprodutivos. Foram utilizadas duplas de machos (MM) e duplas de macho-fêmea (MF) que permaneceram pareadas por 40 minutos. Durante esse período foi feito o registro da interação agonística (10 minutos iniciais e 10 minutos finais do pareamento) e determinado o gasto energético (consumo de O2) pelo Método de Winckler. A latência para o início dos confrontos (média ± DP, MM = 27,40 ± 25,15 s; MF = 14,22 ± 21,19 s; Mann-Whitney, U = 33,50, P = 0,21) e a freqüência de todas as unidades comportamentais (média ± DP, MM < 72,30 ± 25,29; MF < 73,50 ± 21,65.10/min; Mann-Whitney, P > 0,10) foram semelhantes entre os grupos MM e MF nos 10 minutos iniciais. Isso indica que cada intruso foi considerado um potencial competidor no início da interação. No entanto, a freqüência de ondulação (interação também exibida durante a corte) foi maior para o residente do grupo MF nos 10 minutos finais (média ± DP, MM = 3,56 ± 5,89; MF = 8,56 ± 4,00.10/min; Mann-Whitney, U = 15,50, P = 0,01). A freqüência de fuga, entretanto, foi menor para o intruso do mesmo grupo (média ± DP, MM = 3,90 ± 4,33; MF = 0,44 ± 0,96.10/min; Mann-Whitney, U = 23,50, P = 0,04). Além disso, o perfil agonístico no grupo MM foi composto por um maior número de itens comportamentais do que o MF (para residentes e intrusos). Apesar das diferenças comportamentais, o consumo de O2 não foi afetado pela composição sexual do grupo (média ± DP, MM = 1,93 ± 0,54; MF = 1,77 ± 0,46 mgO2.g peso seco-1.40/min; t-teste de Student, t = 0,71, P = 0,49).

Efeito da utilização da levedura desidratada de álcool em dietas para tilápia-do-nilo

Este trabalho teve como objetivo avaliar o efeito da levedura desidratada de álcool (Saccharomyces cerevisae) como substituto do suplemento vitamínico, em dietas de tilápia-do-nilo (Oreochromis niloticus). Trezentos alevinos machos, sexualmente revertidos, com peso médio de 1,5 g, foram distribuídos igualmente em 20 aquários de fibra de vidro, equipados com filtro biológico. Cinco dietas isoprotéicas com 32% de proteína bruta na primeira fase (40 dias) e com 28% de proteína bruta na segunda fase (74 dias) foram fornecidas ad libitum, duas vezes ao dia. A dieta-controle não conti-nha levedura, e as demais apresentavam 10% de levedura. O delineamento foi inteiramente casualizado, com cinco tratamentos e quatro repetições. Não houve influência significativa dos tratamentos sobre o ganho de peso e taxa de crescimento específico. Foi observada, nos peixes alimentados com dietas sem suplemento vitamínico, alta mortalidade. Os peixes que receberam levedura apresentaram menor conteúdo corporal de proteína, e maior, de lipídeos. A levedura desidratada de álcool pode ser usada como fonte de vitaminas hidrossolúveis em dietas para alevinos de tilápia-do-nilo.

Determinação da toxicidade aguda e caracterização de risco ambiental do herbicida Roundup (glifosato) sobre três espécies de peixes

Considering their commercial importance, as these are the species of freshwater fish more commercialized in Brazil, their occurence in different kinds of aquatic environments (lakes, rivers and dams) and for being tolerant to a wide range of variation of various physical parameters and chemical water, the fish species Oreochromis niloticus, Cyprinus carpio and Colossoma macropomum were chosen for this study, furthermore, to test the toxicity we used the herbicide Roundup. The fingerlings of tilapia (Oreochromis niloticus), commun carp (Cyprinus carpio) and tambaqui (Colossoma macropomum) were submitted to the herbicide roundup in the following concentrations: 0.0 (control); 18,06; 19,10; 20,14; 21,18 and 22,22 mg.L-1, 0.0 (control); 13,89; 14,86; 15,83; 16,81 and 17,78 mg.L-1, and 0.0 (control); 18,06; 19,10; 20,14; 21,18 and 22,22 mg.L-1, respectively, three for 96 hours. The LC50 - 96h for O. niloticus, C. carpio and C. macropomum was 21,63, 15,33 and 20,06 mg.L-1 of the herbicide roundup, respectively. The results show that this herbicide is classified as slightly toxic to the three species. The values of dissolved oxygen, pH and temperature recorded in the aquarium control and aquarium experimental of the three fish species have remained without significant variations during the tests, which reduces the possibility of death caused by sudden variations of these parameters during the 96 hours the experiment. The values of LC50 between different species of fish were observed, noting that the species O.niloticus, C. carpio and C. macropomum showed no expressive differences. The values of environmental risk of Roundup were calculated to obtain more stringent parameters in assessing the dangerousness of those on nontargets. The risk of environmental contamination by Roundup for the Nile tilapia, common carp, and tambaqui are low for the lowest application rate (1 L.ha-1) and depths (1.5 and 2.0 m). The dilution of 100%, the highest recommended dose (5 L.ha-1) and depths (1.5 and 2.0 m) the risk is moderate for the three species. The values of the Risk Ratio (QR) were greater than 0,1, indicating that the values of the CAE and LC50 are above acceptable levels and there is a need, this study, a refinement in ecotoxicological tests