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Samples (6404) of Nile perch were collected monthly from commercial catches between June 2014 and June 2015. The total length (cm), weight (g) and sex of fish were all determined in the field, with 3771 (59%) being male and 2059 (32%) being female fish, for an overall sex ratio of 1.83:1.00 (male: female). The average length and weight for all fish...
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Context 1
... fish were 55.38 AE 0.14 cm TL and 2355.10 AE 22.30 g, respec- tively. The size of male fish ranged from 15.5 to 128.5 cm TL and weighed between 190 and 25 000 g, whereas that of females ranged from 21.0 to 130.0 cm TL and weighed between 124 and 25 800 g. The value of the regression slope b of the length-weight relation- ship was equal to 3.04 (Fig. 2). The mean (AESD) condi- tion factor for all fish was 1.23 AE 0.13. The condition factor was different in the length groups, with the high- est (1.32 AE 0.13) and lowest (1.12 AE 0.20) values recorded in length groups 100-110 and <30 cm TL, respectively (Table 2). The highest and lowest condition factors were recorded between January ...
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... This technique has higher chances of reducing fish markets' information asymmetry and increases the opportunities for on-time availability of funds and loans through the use of digital banking systems and mobile money services. Thus, digital financial services reduce the gap of physical financial services in funding fisheries (Repo, 2015;Schaape, 2019;Yongo et al., 2017). ...
... On the contrary, there are limited empirical studies on the impacts of communication technology adoption and its impact on the welfare of fishers' communities around Lake Victoria and Tanzania in general. Several studies conducted on Lake Victoria (Mkuna & Baiyegunhi, 2020;Taabu-Munyaho et al., 2016;Yongo et al., 2017) focused on the impact of overfishing, but did not address the impacts of technology adoption on Lake Victoria fishers' welfare. Thus, examining the effects of technology adoption among Nile perch fishers' welfare (income) is necessary and important. ...
... However, these findings are inconsistent with research conducted in other countries, which has consistently shown that women not only use technology but are also early adopters who buy more than men (Orser & Riding, 2018;Wirthman, 2018;Yongo et al., 2017 (2019) and Repo (2015) have also shown that owning modern smartphones increase the likelihood of utilizing digital fish markets. ...
Despite the growing importance of digital technology in modern society, its adoption in some sectors and regions has been slow. One such sector is fishing in developing countries, where the potential benefits of technology have yet to be fully realized. This study examines the adoption of communication technology among Nile perch fishers on Lake Victoria in Mwanza, Tanzania. Using a Probit model and Ordinary Least Square (OLS) estimations with Robust Standard Errors (OLSR), the study analyzes the impact of technology adoption on fishers' welfare, with a focus on income. The results suggest that the type of mobile phone, fishing experience, and the desire to exploit digital marketing are key factors in technology adoption among fishers. Furthermore, the study finds that technology adoption has a significant positive impact on fishers' welfare, indicating that digitalization can increase market competitiveness, openness, and improve livelihoods. To capitalize on these benefits, the study recommends that the government should support the digitalization of the fishing market and make accurate and timely market information readily available to fishers.
... There are many malignant invasive fish species globally, including common carp, walking catfish, mosquito fish, Nile perch, brown trout, rainbow trout, largemouth bass, and the tilapia species (Canonico et al., 2005;Gozlan, 2008;Yongo, Outa, Kito, & Matsushita, 2017). Tilapias are native to Africa and the Middle East but have been introduced in other regions to enhance capture fisheries and aquaculture (Canonico et al., 2005;Cishahayo et al., 2022;Yongo et al., 2022). ...
Tilapia invasion has become a significant concern to ecologists and conservationists, posing severe threat to freshwater biodiversity. Many tilapia species have been introduced to China since 1957, with some having invaded freshwater ecosystems in South China. Accordingly, the present review examined the driving factors for successful tilapia invasion and their ecological impacts, information essential for practical management purposes. This review identified aquaculture as the main pathway spreading tilapias into the wild freshwater systems through their escape and release. Their biological and life history traits, including flexible habitat requirements, environmental tolerance, and generalist feeding are essential factors facilitating their ability to inhabit varying habitats. Biodiversity loss and habitat degradation further promote tilapia invasions by creating exploitable habitats for them, noting their considerable tolerance to degraded ecosystems. Regarding ecological effects, tilapias stimulate phytoplankton growth by increasing nutrient concentrations in the water column through excretion and bioturbation. Tilapias also depress benthic algal growth by promoting sediment resuspension, deteriorating water quality, and enhancing eutrophication. Moreover, tilapias cause the decline of native fish species biomass through competition and may threaten fish biodiversity. The findings in the present review suggest direct removal of tilapias can be a useful practice for controlling them. Furthermore, imposing regulations on tilapias introductions, efficient aquaculture management, and biodiversity conservation should also be considered in controlling and preventing the invasion and spread of tilapias.
... Parameters such as length-weight relationships and condition factors are important for studying the biology of fishes (Lizama et al., 2002;Yongo et al., 2017) and can be used to predict the weight of fish from length measurements obtained from stock assessments (Pauly, 1993). The length-weight relationship and condition factor are also important parameters for assessing the health condition of fish (Mortuza & Al-Misned, 2013;Nehemia et al., 2012). ...
... The relative condition factor variations may be partly attributable to the differences in ecological conditions between the water bodies and also the species type (Froese, 2006;Yongo et al., 2017). ...
Oreochromis leucostictus is a commercially important tilapiine in Lake Naivasha, with
its stocks having declined because of the effects of fishing, habitat degradation and
pollution. The present study investigated its length–weight relationship, condition
factor, sex ratio and maturity. Fish samples (233) were collected during 2017, with
each fish measured (cm), weighed (g) and analysed for maturity in the laboratory. The
mean (±SD) total length and weight were 21.3 ± 0.3 cm TL and 187.4 ± 8.3 g, respectively. The fish exhibited a negative allometric growth pattern (b = 2.33). The mean
condition factor was 1.06, 0.99 and 1.04 for male, female and combined sexes, respectively. The condition factor was significantly higher in September (1.70 ± 0.15)
and October (1.63 ± 0.15) than in other months. Males were significantly more dominant than females (male:female sex ratio = 2.19:1.0). Females (21.0 cm TL) matured
at smaller lengths, compared to males (26.0 cm TL). Comparisons with earlier studies
suggested the length–weight relationship, condition factor, sex ratio and size at first
maturity of O. leucostictus in Lake Naivasha varied significantly from other tilapiines
in various water bodies. The results of the present study provide insights into the biological attributes of O. leucostictus useful for its sustainable management
... Parameters such as length-weight relationship and condition factor are important for studying the biology of fishes (Lizama & Ambrosia, 2002;Yongo et al., 2017) and can be used to predict fish weight from length measurements obtained from stock assessments (Pauly, 1993). The length-weight relationship and condition factor are also F I G U R E 2 Catch composition of male and female Oreochromis niloticus, Oreochromis leucostictus and Coptodon zillii by different mesh sizes from Lake Naivasha, Kenya (TL indicates total length) important parameters for assessing the health condition of fish (Mortuza & Al-Misned, 2013;Nehemia et al., 2012). ...
The Nile tilapia (Oreochromis niloticus), Redbelly tilapia (Coptodon zillii) and Blue spotted tilapia (Oreochromis leucostictus) were introduced into Lake Naivasha in the 1950s to diversify and boost the lake fisheries. These species have since been exploited in the commercial gillnet fishery. The fish stocks, however, are currently facing problems of pollution, wetland degradation and intense fishing pressures. Accordingly, the present study investigated some aspects of the biology and population structure of the three tilapiine species in light of changing lake conditions. Fish samples were collected from January to December 2019 using multifilament gillnets of 2.0-to-6.0-inch mesh sizes. Immediately after their capture, the fish specimens were transported to the lab for morphometric measurements and analysis of maturity. The highest and lowest mean (±SD) total length (TL) were exhibited by O. niloticus (22.9 ± 5.2 cm) and C. zillii (14.5 ± 2.1 cm), respectively. Similarly, O. niloticus exhibited a higher mean weight (268.4 ± 18.0 g) and body depth (7.6 ± 2.5 cm), compared to the other species. O. niloticus exhibited an isometric growth pattern, while C. zillii and O. leucostic-tus exhibited negative allometric growth. The fish species were in good condition, with mean condition factors of 1.59 ± 0.07, 1.51 ± 0.06 and 1.23 ± 0.03 for C. zillii, O. leucostictus and O. niloticus, respectively. Furthermore, the condition factors for O. leucostictus and O. niloticus varied by size class, exhibiting a decreasing trend with increased fish size. The male:female sex ratio revealed significantly more males than females for O. niloticus (2.30:1.0) and O. leucostictus (2.36:1.0), although not for C. zillii (1.15:1.0). O. niloticus (28.0-29.0 cm TL) matured at a larger size, followed by O. leu-costictus (21.0-26.0 cm TL), and C. zillii (15.0-17.0 cm TL). In comparison, values of length-weight parameters, condition factor, sex ratio and size at first maturity of the studied fishes varied in Lake Naivasha, Victoria, Albert and George. The gillnet mesh ≤3.0″ mainly targeted small-sized immature fish, while mesh ≥4″ targeted mature fish, particularly O. niloticus. It was concluded that gillnets with ≥4.0″ mesh could safely be applied for this fishery in Lake Naivasha, whereas the use of smaller mesh should be controlled to protect the juveniles as a means of maintaining sustainable fisheries. Furthermore, the present study also provided useful information, including size at maturity that is vital for setting mesh size for managing the lake fishery.
... In a study of the Nile perch value chain, Bagumire et al., (2018) indicates that in the first stage of the value chain, at the beach, fish of processable quality and allowable slot-size is sold directly to factory agents, whilst poor quality fish and fish below and beyond the allowable size are then sold to the local traders. The allowable fish slot sizes of 50-85 cm correspond to about 2-10 kg fish from fish sampled in other commercial vessels [63,64], which also coincides with the modal fish size of the motorized fishers in this study. Fishers have mastered strategies, and with the use of triple panel gillnets, they were able to obtain fish sizes within this range ( Figure 8). ...
... Besides, currently in Uganda and Lake Victoria, there is an emerging fish maw industry, where the value of the fish maw increases with the size of the Nile perch. Nile perch beyond the factory allowable size limit >85 cm TL are targeted for the fish maws and their price per kg (50 USD) is 10 times more than that of fish fillets (5 USD) [64]. Unregulated fishing of large fish sizes threatens the population of the spawning stock. ...
Sustainable management of fisheries has proven to be a daunting exercise for Lake Victoria. Exploitation patterns in the fishery are driven by fishers who adopt different strategies as a response to changing economic, management, socio-economic, and resource conditions. Fisheries managers, however, seldom consider these changes in management policies. The aim of the study, therefore, was to evaluate the adaptation strategies of the Nile perch gillnet fishers on Lake Victoria in Uganda using 8-year catch and effort data collected in the period from 2005 to 2015. Trends of the selected
effort and catch variables in the study period identified two adaptive fishing strategies by gillnet fishers on the lake. The first group, the paddled fishermen whose gillnet use varied in the first half of the study, diverted to harvesting juvenile Nile perch by using smaller, mesh sizes, monofilament nets and gillnets of less depth in the second half of the study. Motorized fishers, on the other hand, maintained their mesh size, using multifilament gillnets, however, they increased the depth of their nets in the second half of the study period to maintain their targeted fish size. Fishers on Lake Victoria adapted strategies to cope with their constraints and opportunities based on the Nile perch population
structure and their economic needs. It is important for fishery managers to consider that the fishers are an integral part of the fisheries ecosystems, and considering their behaviour in management decisions will aid in devising adaptive policies for sustainable resource use and sustainable livelihood development of the fishers’ communities.
... considered for commercial value, as well as to promote fishery activities and related livelihood of fishers around the lake (Aloo et al., 2017;Njiru et al., 2014;Yongo et al., 2017). ...
... Thus, every fisher who fished had an average weight of less than 2.1 kg per individual fish, meaning a TL below 50-cm was considered to have been overfished. This measurement was also supported by conventional measurements of weight and length following the studies of Ogutu-Ohwayo (1999) and Yongo et al. (2017), who reported a Nile perch with an average length of 55.38-cm TL weighs 2355 g (2.4 kg). To determine the impacts of Nile perch overfishing on the fishers' technical efficiency, the Average Treatment on Treated (ATT) technique was used to compare the overfishing Nile perch fishers to those who were not overfishing, following the Propensity Score Matching (PSM) method as adopted from Rosenbaum and Rubin (1983), Khandker et al. (2010) and Putra et al. (2017). ...
The present study employed the Data Envelopment Analysis (DEA) and Propensity Score Matching (PSM) techniques to assess the impacts of Nile perch overfishing on the technical efficiency of fishers, based on a survey of 268 fishers across ten landing sites in the Tanzanian portion of Lake Victoria. The DEA results indicated overall that Nile perch fishers exhibited an average technical efficiency of 30%, indicating a high level of inefficiency. There were no statistically significant differences in the technical efficiencies within the range of 0%–10% and 21%–30% for Nile perch fishers who were overfishing and those who were not overfishing, attributed to the fisher's mobility across the lake. Further, the mode of propulsion and being a member of a fishery organization were found to be statistically significant factors influencing the inefficiency of Nile perch fishers. In addition, results from the Probit estimates of the PSM indicated that being a member of a fishery organization, the quantity of Nile perch harvested per trip, the age of a fishing vessel (boat), the gillnet mesh size and the cost of fishing inputs had statistically significant effects influencing the probability of Nile perch overfishing. However, further results indicated Nile perch overfishing did not have a statistically significant impact on the technical efficiency of fishers. Thus, it is recommended that there is a need to monitor and formalize fisher's mobility as one of the alternatives for co-management of the lake. Overfishing could be controlled without necessarily affecting the technical efficiency of Nile perch fishers through training and access to proper fishing gears.
... Catches of B. docmak in Lake Victoria have strongly declined after the upsurge of Nile perch (Lates niloticus) (Balirwa et al., 2003;Yongo et al., 2017) and concomitant ecological changes, with B. docmak currently restricted to refugia in rocky habitats and mouths of large rivers. Predation by, and competition with L. niloticus for haplochromines as food, might have played a role in their decline (Balirwa et al., 2003;Ogutu-Ohwayo, 1990). ...
... Parameters, such as the length-weight relationship and condition factor are important for studying the biology of fishes (Lizama et al., 2002;Yongo et al., 2017). They can be used to predict the weight of fish from length measurements obtained from stock assessments (Pauly, 1993). ...
Bagrus docmak is indigenous to Lake Victoria, being an important source of economic livelihoods to communities around the lake. Although its stocks in the lake
are facing intense fishing, predation and ecological changes, data on its biological
aspects are scanty, being the basis for the current study. Fish samples for the present study were collected using gillnets of 10- and 50-mm mesh sizes. The length
and weight of individual fish caught were measured in the field, while stomachs
were preserved in 5% formalin and taken to the laboratory for gut content analysis.
The overall sex ratio (male: female) was 1.0:1.26, and did not deviate significantly
from 1:1. The lengths of the fish ranged from 12.0 to 55.0 cm TL and the weights
ranged between 20.0 and 1650.0 g, with a mean length and weight of 32.7 cm TL
and 351.2 g, respectively. The fish were in a good condition with mean condition
factors (K) of 1.0, 1.01 and 0.97 for all fish, females and males, respectively. The
fish exhibited a negative allometric growth pattern, with a length–weight relationship slope (b) of 2.90, 2.94 and 2.94 for all fish, females, and males, respectively. Stomach analyses revealed an ontogenetic diet shift, where juveniles of less than
30 cm TL feeding exclusively on Caridina nilotica. With increasing size, the fish ingested insects and other fish species, including barbus, bivalves, haplochromines,
crabs and detritus in variable quantities. The results of the present study provide
useful information on the biological aspects of B. docmak useful for its management
and comprehensive stock assessment when required. It also provides insights into
the feeding ecology of this fish in view of the changing Lake Victoria ecosystem.
Accurate Knowledge regarding its food requirements can inform feed formulation
for its successful culture
... The local communities in the catchment have relied on Lake Victoria for their livelihood for centuries. Before the introduction of exotic species, Lake Victoria had a multispecies fishery that comprised >500 endemic fish species, dominated primarily by the tilapiines O. esculentus and Oreochromis variabilis and, haplochromine cichlids (Ogutu-Ohwayo 1990 Lates niloticus was introduced from Lake Albert into the Ugandan and Kenyan parts of Lake Victoria between 1954 and 1963, with the aims of creating a recreational fishery and converting the large biomass of the indigenous small bony haplochromine cichlids into a less-productive but more valuable resource (Pringle 2005;Yongo et al. 2017a).Haplochromine cichlids were the dominant fish in Lake Victoria during the 1970s, forming the major prey item for the introduced L. niloticus ( Figure 1). However, from 1970s to 1989 there was a boom in L. niloticus abundance that coincided with the decline of the endemic haplochromine cichlid species (Figure 2). ...
This paper discusses the catch trends, population attributes and biological characteristics of tilapiine species
that are both native and that have been introduced into Lake Victoria and Lake Naivasha. Predation by Lates
niloticus, species hybridisation, overfishing, pollution and eutrophication have negatively impacted endemic fish
stocks in these lakes. Four tilapiine species, Oreochromis niloticus, Oreochromis leucostictus, Coptodon zillii and
Coptodon rendalli, and three tilapiine species, O. niloticus, C. zillii and O. esculentus, were hence introduced into
Lake Victoria and Lake Naivasha, respectively, to improve fish catches following collapse of native fish stocks.
Establishment of these non-native species was associated with declines in populations of the native Oreochromis
esculentus and Oreochromis variabilis, and O. niloticus now dominates commercial tilapiine fishery in Lake
Victoria. The fishery catches in Lake Naivasha were dominated by the introduced O. leucostictus and O. niloticus,
whereas C. zillii is rarely caught. The biological and population attributes of the tilapiines in both lakes have shown
great variations over time. There is, therefore, a need for implementation of effective management measures,
including control of fishing effort, pollution control and protection of surrounding wetlands, to promote recovery
and long-term sustainability of the fishery resources of these lakes.
... The local communities in the catchment have relied on Lake Victoria for their livelihood for centuries. Before the introduction of exotic species, Lake Victoria had a multispecies fishery that comprised >500 endemic fish species, dominated primarily by the tilapiines O. esculentus and Oreochromis variabilis and, haplochromine cichlids (Ogutu-Ohwayo 1990 Lates niloticus was introduced from Lake Albert into the Ugandan and Kenyan parts of Lake Victoria between 1954 and 1963, with the aims of creating a recreational fishery and converting the large biomass of the indigenous small bony haplochromine cichlids into a less-productive but more valuable resource (Pringle 2005;Yongo et al. 2017a).Haplochromine cichlids were the dominant fish in Lake Victoria during the 1970s, forming the major prey item for the introduced L. niloticus ( Figure 1). However, from 1970s to 1989 there was a boom in L. niloticus abundance that coincided with the decline of the endemic haplochromine cichlid species (Figure 2). ...
This paper discusses the catch trends, population attributes and biological characteristics of tilapiine species
that are both native and that have been introduced into Lake Victoria and Lake Naivasha. Predation by Lates
niloticus, species hybridisation, overfishing, pollution and eutrophication have negatively impacted endemic fish
stocks in these lakes. Four tilapiine species, Oreochromis niloticus, Oreochromis leucostictus, Coptodon zillii and Coptodon rendalli, and three tilapiine species, O. niloticus, C. zillii and O. esculentus, were hence introduced into
Lake Victoria and Lake Naivasha, respectively, to improve fish catches following collapse of native fish stocks.
Establishment of these non-native species was associated with declines in populations of the native Oreochromis
esculentus and Oreochromis variabilis, and O. niloticus now dominates commercial tilapiine fishery in Lake Victoria. The fishery catches in Lake Naivasha were dominated by the introduced O. leucostictus and O. niloticus, whereas C. zillii is rarely caught. The biological and population attributes of the tilapiines in both lakes have shown
great variations over time. There is, therefore, a need for implementation of effective management measures,
including control of fishing effort, pollution control and protection of surrounding wetlands, to promote recovery
and long-term sustainability of the fishery resources of these lakes.
... Fishers were asked about the average weight in kilogram (kg) of individual Nile perch harvested by them per trip. The conventional measurement of weight and length was then done, following studies by Ogutu-Ohwayo (1999) and Yongo et al. (2017), who found that a Nile perch with an average length of 55.38 cm TL weighs 2 355 g (2.4 kg). Using this length-weight relationship would imply that the minimum slot size of 50 cm TL will weigh 2 141 g (2.1 kg). ...
Despite the crucial role played by Nile perch in the income of fishers around Lake Victoria, Tanzania, fishing pressure has increased in recent years and has led to overfishing and, consequently, a risk to the lake’s future sustainability and the fishers’ livelihoods. This study used data collected in 2018 from 268 randomly selected sample fishers at 10 landing sites across Lake Victoria. In conjunction with the endogenous switching regression model, the potential impact of Nile perch overfishing on the fishers’ income per fishing trip in Lake Victoria was evaluated. The results show that there is a significant difference in the socio-economic, institutional and fishing effort characteristics of Nile perch fishers who overfish and those who do not. In particular, Nile perch fishers who overfish earn significantly higher incomes per fishing trip than fishers who do not overfish. The study recommends the need for policy makers to develop policies that acknowledge the dynamics of socio-economic, institutional and fishing effort factors. In addition, more flexible fish quota restrictions and consistent fishing patrols need to be enforced to ensure compliance with fishery regulations. These measures should promote a balance between the sustainability of fishery resources and an improved income for Nile perch fishers in Lake Victoria.
