Odonata Nymphs Research Articles

A decadal-scale qualitative comparison of lotic Odonata nymph surveys in northwestern Pennsylvania, USA, reveals possible assemblage restructuring

Detecting long-term changes to Odonata assemblages requires repeated sampling at fixed locations over decadal periods. However, few such biomonitoring efforts exist for Odonata, especially at low taxonomic resolution and immature life stages. We repeated a survey of Odonata nymphs conducted nearly thirty years ago in ten streams from a northern Pennsylvania forest reserve to qualitatively explore assemblage-scale changes and identify streams supporting species of conservation concern. Our survey collected five more species among all sites than the original survey, reflecting a 15% increase in richness despite a reduced sampling effort. Rank abundances of many species changed substantially between surveys. Some, such as Calopteryx maculata, fell in rank while other species like Boyeria vinosa and Phanogomphus lividus that were rare in 1994 became the most numerically dominant. We did not detect patterns in species richness or changes in richness between surveys along gradients of unconventional natural gas extraction or timber harvest among streams. The fraction of species deemed vulnerable or imperiled within Pennsylvania grew from 22 to 38% between surveys, highlighting the regional conservation value of protected area we sampled. Our sampling methodology precludes population estimates or quantitative community comparisons due to the sampling design and inconsistencies in the literature used for identification between surveys. However, the substantial differences in rank-abundance among species between surveys suggests potential long-term changes in these lotic Odonata assemblages. The collective findings presented here emphasize the high value of data from repeated surveys with species-level taxonomic resolution.

Effects of different prey on larval growth in the diving beetle Cybister sugillatus Erichson, 1834 (Coleoptera: Dytiscidae)

The population size of the diving beetle Cybister sugillatus Erichson 1834 (Coleoptera: Dytiscidae) has been declining in Japan; therefore, there is a need to understand their fundamental ecology for conservation purpose. Understanding the feeding habits in the larval stage will contribute to habitat restoration and ex situ conservation. In this study, we investigated the effects of the availability of different kinds of prey, such as Odonata nymphs and tadpoles, on larval growth of C. sugillatus. The results showed that Odonata nymphs were the preferred prey for larval growth because C. sugillatus larvae did not show significant growth on tadpoles alone. This trend was also observed in other Cybister species. Our results suggest that habitat restoration requires the development of an environment rich in a variety of aquatic invertebrates, including Odonata nymphs. In ex situ conservation, stable rearing and breeding of C. sugillatus can be made possible by providing them with Odonata nymphs as food.

Larval feeding habits of the large‐bodied diving beetle Cybister rugosus (Coleoptera: Dytiscidae) under laboratory conditions

AbstractThe population of the diving beetle Cybister rugosus (Macleay, 1825) has been declining in recent years, and it is designated as “Vulnerable” (VU) in the Red List of Japan. However, there have been no quantitative studies on the feeding habits of the larval stage of this beetle. Revealing the feeding habits is indispensable for understanding the life history of C. rugosus. In the current study, we reared C. rugosus larvae on different prey taxa (Odonata nymph, fish, tadpole, and shrimp) and evaluated their growth and survival rates. Previous studies have shown that three congeneric Cybister species larvae feed mainly on invertebrates. However, all larval instars of C. rugosus were able to feed on invertebrates and vertebrates and grow. Thus, we considered C. rugosus to be a generalist compared to the other Cybister species. The larval periods were shorter for C. rugosus that fed on Odonata nymphs than on any other prey. Feeding different prey taxa had no significant effect on the body length of newly emerged adult males. However, the body length of newly emerged adult females was larger when the larvae fed on Odonata nymphs than when the larvae fed on fish. As in other Cybister species, we concluded that the Odonata nymph is an appropriate food from the viewpoint of increased growth rate in C. rugosus.

Predicting the habitat suitability of Schistosoma intermediate host Bulinus truncatus, its predatory aquatic insect Odonata nymph, and the associated aquatic plant Ceratophyllum demersum using MaxEnt.

Schistosomiasis is one of the most important parasitic diseases in tropical and subtropical areas. Its prevalence is associated with the distribution of freshwater snails, which are their intermediate hosts. Thus, control of freshwater snails is the solution to reduce the transmission of this disease. This will be achieved by understanding the relationship between the snails and their habitats including natural enemies and associated aquatic plants as well as the factors affecting their distribution. In this study, Maximum Entropy model (MaxEnt) was used for mapping and predicting the possible geographic distribution of Bulinus truncatus snail (the intermediate host of Schistosoma haematobium), Odonata nymph (predatory aquatic insect), and Ceratophyllum demersum (the associated aquatic plant) in Egypt based on topographic and climatic factors. The models of the investigated species were evaluated using the area under receiver operating characteristic curve. The results showed that the potential risk areas were along the banks of the Nile River and its irrigation canals. In addition, the MaxEnt models revealed some similarities in the distribution pattern of the vector, the predator, and the aquatic plant. It is obvious that the predictive distribution range of B. truncatus was affected by altitude, precipitation seasonality, isothermality, and mean temperature of warmest quarter. The presence of B. truncatus decreases with the increase of altitude and precipitation seasonality values. It could be concluded that the MaxEnt model could help introducing a predictive risk map for Schistosoma haematobium prevalence and performing better management strategies for schistosomiasis.

Community assembly of adult odonates in lacustrine systems of an understudied world heritage site of south-eastern Zimbabwe

Odonata (dragonflies and damselflies) are efficacious for management and conservation efforts in freshwaters. In recent times, increased effort has gone into enhancing awareness, data and information on dragonflies among scientists and policymakers. Here, we examined the Odonata community of dams within the Matobo National Park, a world heritage site in southern Zimbabwe. Specifically, we determined diversity of larval and adult odonate in five dams over one year. Several physico-chemical parameters were measured, including pH, total dissolved salts (TDS), electrical conductivity (EC). Further, we assessed how habitat types (i.e., detritus, sand, gravel, plant type) affect Odonata communities. In addition, surveys were conducted to identify critical threats to Odonata in the Matobo National Park and surrounding areas. Broadly, results showed that Odonata nymphs and volant adults did not change predictably across all sampling occasions. Further, pH was positively correlated with Libellulidae and Platycnemididae, whereas TDS and EC were positively correlated with Libellulidae, Platycnemididae and Macromiidae. Contrariwise, Gomphidae were found to be negatively correlated to TDS, EC and pH. The threat analyses identified natural system modifications, agricultural expansion and intensification, as well as human intrusions and disturbance as the major threats to Odonata and freshwater resources in Matobo National Park. Taken together, these data provide baseline data that will be useful for future monitoring of threats and subsequently conservation strategies in the Matobo National Park and other protected areas in Southern Africa.

Importation of Dragonfly Nymphs (Odonata: Anisoptera) to Control Mosquito Larvae (Diptera: Culicidae) in Southern Maine

A long-standing program in Maine promotes stocking of dragonfly (Odonata) nymphs for biological control of nuisance and vector mosquitoes. Currently the only sources of dragonflies for stocking are out-of-state biological supply companies. In 2 dragonfly shipments from suppliers in Massachusetts and North Carolina, we determined that 6.8% and 38.5% of species, respectively, were not native to Maine. In an experiment of stocking efficacy, we introduced 4, 2, or 0 dragonfly nymphs into artificial pools in a forest habitat and found no differences in mosquito larvae counts among treatments. While the motivation for using dragonflies as biological control agents is commendable, the practice may be ineffective, and risks accidental introductions of non-native aquatic plants and animals in water used for shipping.

Water quality effects on dragonfly and damselfly nymph communities: A comparison of urban and natural ponds

Cities are increasingly using constructed ponds to mitigate flooding and downstream water pollution from urban runoff. As a result, these stormwater ponds can have poor water quality, yet they can also attract wildlife. In this study, the effects of water quality on dragonflies and damselflies (Odonata) were determined in stormwater ponds (n = 41) and natural reference ponds (n = 10) of similar size across the National Capital Region of Canada. A total of 38 chemical/physical water quality variables along with Odonata nymph abundance and taxonomic composition were sampled at each pond. Chloride concentrations exceeded the guideline for the protection of aquatic life at over two-thirds of the stormwater ponds. Among all the metals tested, only Cu exceeded guidelines at many stormwater ponds. Both dragonfly and damselfly nymphs were on average less abundant in the stormwater ponds in comparison to the natural ponds. Ponds with high concentrations of chloride and metals typically had lower dragonfly abundance. Dragonfly community structure was significantly influenced by high chloride (or conductivity), which likely originates from winter road salting. In contrast, damselfly community structure in the stormwater ponds was similar to that found in natural ponds, with nutrients and metals explaining a small percent of variation in community structure. A water quality index developed to assess habitats for the protection of aquatic life did not significantly explain Odonata abundance or measures of diversity and may not be suitable in assessing pond habitat quality. To improve pond habitats within cities, efforts should be directed at reducing the amount of impervious surface and road salt usage within catchment basins.

Antagonistic effects of a native apple snail on other snails and macroinvertebrates in Southern Pampas waterbodies: A mesocosm approach

Macroinvertebrates represent an important component of communities and trophic webs of freshwater ecosystems. Pomacea canaliculata (family Ampullariidae), an invasive apple snail native to the Pampas ecoregion, acts as a voracious grazer and plays a structuring role on submerged macrophytes that serve as food, habitat or foraging ground for many macroinvertebrates. Laboratory studies show that P. canaliculata can also act as a competitor or predator of other macroinvertebrates. Using a mesocosm approach, we sought to investigate if this species of apple snail affects other freshwater snails (Chilina parchappii, Heleobia parchappii, Biomphalaria peregrina and Melanoides tuberculata) as well as other macroinvertebrates and if consumption of submerged macrophytes and detritus mediates these effects. After twelve weeks we estimated in mesocosms with and without apple snails the abundance of snails and macroinvertebrates through samples taken separately from sediment and from macrophytes. We also estimated the coverage and biomass of macrophytes and the detritus biomass. Significantly lower abundance occurred in mesocosms with apple snails for all snail species and representative macroinvertebrates (i.e., Hirudinea, Ephemeroptera, Chironomidae and Odonata). Mesocosms with apple snails also resulted in lower total abundance of macroinvertebrates. We speculate that the negative effects of P. canaliculata on most other snails and macroinvertebrates living on macrophytes relates to their grazing on detritus and macrophytes. In contrast, the density of snails and macroinvertebrates in the samples from sediments were not affected by P. canaliculata. One snail species and Ephemeroptera were negatively affected by mechanisms not related to the reduction in macrophyte biomass and detritus. A decrease in the microhabitats provided by macrophytes probably mediated the negative effects on Odonata nymphs. The reduction in the abundances of snails and macroinvertebrates caused by P. canaliculata may have cascading effects on higher trophic levels in waterbodies from Southern Pampas but also in invaded regions.

Are Odonata nymph adversely affected by impaired water quality in urban streams

AbstractGlobally 10% of all dragonfly species are threatened by extinction that can be primarily attributed to a loss of natural habitat. Urban expansion and the associated urban stream syndrome has established that the extent and intensity of urban development is directly linked to a range of adverse physical, chemical and ecological changes. Urban waterways typically experience degraded water quality and are occupied by impaired communities of aquatic invertebrates which are mostly dominated by rapid colonizing insects. Odonata are a diverse insect group and their tolerance or sensitivity to urban waterway degradation is unclear. This research examined the response of aquatic macroinvertebrate communities and specifically the Odonata nymph community to impaired water quality and degraded riparian vegetation condition in streams of the Georges River catchment, Sydney, across an urban development gradient. Unlike the overall macroinvertebrate community, Odonata nymph species assemblages were not strongly linked to the urban development gradient nor the degree of degradation in water quality. This result diverges from many aquatic macroinvertebrate studies that have reported a correlation between the response of Odonata taxa to degraded water quality. Our findings conclude that Odonata nymph community alone are not a suitable indictor of urban stream degradation as measured by water quality or catchment imperviousness and that the conservation of urban dragonflies should place a greater focus on the conservation and creation of suitable habitats.

Diet and helminth parasites of freshwater turtles Mesoclemmys tuberculata , Phrynops geoffroanus (Pleurodira: Chelidae) and Kinosternon scorpioides (Criptodyra: Kinosternidae) in a semiarid region, Northeast of Brazil

In this study, the Kinosternon scorpioides , Mesoclemmys tuberculata and Phrynops geoffroanus freshwater turtles collected in the Carius River, State of Ceara, were analysed as to their diet composition and presence of helminths. Among the 63 examined turtles 55 (87.3%) were parasitized. We found three Nematoda species ( Physaloptera retusa , Serpinema monospiculatus and Spiroxys figueiredoi ) and one Trematoda species ( Gorgoderina sp.). Phrynops geoffroanus had the highest indexes of prevalence (97.56%) and mean intensity of infection (33.5), followed by M. tuberculata (70% and 12.64, respectively) and K. scorpioides (50% and three, respectively). Host body size was positively related to helminths abundance in both male and female Chelidae species. A significant difference in helminths abundance between the sexes was found only in P. geoffroanus , where females had more parasites than males. Regarding diet, the main food items ingested by M. tuberculata were Odonata nymphs (Aeshnidae and Libellulidae), whilst P. geoffroanus feeds mainly on Diptera larvae (Chironomidae), Odonata nymph (Aeshnidae) and Notonectidae, and only seeds were found in the stomach contents of K. scorpioides . Here, we present the first record of S. monospiculatus parasitizing K. scorpioides , Gorgoderina sp. and P. retusa were reported for the first time in P. geoffroanus , and M. tuberculata represents a new host to P. retusa and S. figueiredoi .

Experimental evaluation of Odonata nymph in the biocontrol of schistosomiasis intermediate hosts

ObjectiveTo evaluate the predatory potential of the Odonata nymph on freshwater snails that serve as intermediate hosts for Schistosoma species (Bulinus truncatus and Biomphalaria alexandrina). MethodsObservations on the searching, attacking and devouring of the two snail types with series of laboratory-based predation experiments, whose aims were to determine daily predation rate, differential predation, prey preference considering small-, medium- and large-sized snails were conducted. ResultsLaboratory evaluation revealed that, the Odonata nymph could kill and consume the two intermediate hosts. The number of snails consumed differed according to the snail type, size and density. The times taken for searching and handling times were dependent on the snail size, type and satiation of the predator. The predation rate varied also with respect to snail type, size and density. This study also evaluated that Odonata nymphs consumed more Bulinus truncatus than Biomphalaria alexandrina per unit time, and that there may be a preference for smaller than larger snails. ConclusionsAccording to our observation, the predator, Hemianax ephippiger nymph may be a suitable biocontrol agent in connection with Schistosoma intermediate hosts.

Response of benthic macroinvertebrate assemblages to round (Neogobius melanostomus, Pallas 1814) and tubenose (Proterorhinus semilunaris, Heckel 1837) goby predation pressure

One of the main assumed impacts of invasive gobies is predation on benthic macroinvertebrates. Despite numerous dietary studies, however, quantitative evaluations of impact in European river systems are scarce. Here, we investigate the impact of tubenose (Proterorhinus semilunaris, Heckel 1837) and round (Neogobius melanostomus, Pallas 1814) gobies on macroinvertebrates in a lowland river (River Dyje, Czech Republic) by allowing and preventing gobiid access to rip-rap substrate naturally colonised by invertebrates at two sites (Site 1—tubenose goby only, Site 2—tubenose and round gobies). Gobies had a negative impact on invertebrates at both sites, with overall invertebrate density reduced by 15% (ca. 17.9 g m−2 per year) at Site 1 and 36% (ca. 23.6 g m−2 per year) at Site 2. Both species showed increased impact in summer and ingested larger invertebrates preferentially, resulting in an overall reduction in invertebrate body size. Tubenose gobies had a significant impact on Annelida, Gastropoda, Crustacea and Ephemeroptera nymphs, while tubenose and round goby together impacted Annelida, Bivalvia (Dreissena), Gastropoda, Crustacea, Ephemeroptera nymphs, Odonata nymphs and Chironomidae larvae. Our results confirm that round and tubenose gobies can have a significant negative impact on aquatic invertebrate density and community composition.

Potential of Hemianax ephippiger (Odonata-Aeshnidae) nymph as predator of Fasciola intermediate host, Lymnaea natalensis

ObjectiveTo evaluate the predatory capacity of the Odonata, Hemianax ephippiger nymph as a biocontrol agent for the freshwater snail Lymnaea natalensis, intermediate host of Fasciola gigantica. MethodsObservations on the searching, attacking and devouring of the snails with a series of laboratory-based predation experiments, whose aims were to determine daily predation rate, differential predation on small-, medium- and large-sized snails were carried out. ResultsLaboratory evaluation revealed that, the Odonata nymph could kill and consume all three sizes of snails. Searching and handling time of the predator differed depending on snail size and predator vulnerability. The predation rate varied also with respect to snail size and density. ConclusionsOur observations suggested that the predator Hemianax ephippiger may be a suitable bio-control agent of Lymnaea natalensis snail population.

Trophic scaling of Percichthys trucha (Percichthyidae) in monospecific and multispecific lakes in western Patagonia

Percichthys trucha is a freshwater fish, endemic to southern South America and widely distributed in both, eastern and western sides of the Andes. P. trucha has been described as top native predator in lacustrine ecosystems, experimenting diet shifting during their life history development. Salmonid invasions have impacted their natural ecology through trophic niche interference and predation over alternative high quality prey. This study focuses on populations of P. trucha in western Patagonia, where its trophic ecology have been less understood. We hypothesised a diet shift between juveniles and adults from lower-trophic position prey towards higher-trophic position prey. Fish were collected from 7 lakes belonging to Puelo and Baker river basins, covering a high diversity of environmental conditions. Stomach content and δ 15 N stable isotope ratio of muscle tissues of 313 individuals were analysed. Results indicate significant differences in diet between juveniles and adults, shifting from planktonic/benthic preys towards benthic/piscivory, and concomitantly enrichment in heavier nitrogen isotope suggest trophic scaling. No trophic scaling was observed in populations inhabiting lakes with any other fish species present, essentially due to lack of Galaxias sp. as available prey and absence of cannibalism. Despite the fact that P. trucha and Galaxias sp. co-occur in studied river basins, no salmonid-free lakes harbouring this two native species were found, making it difficult to elucidate exact effects of salmonids on trophic scaling of P. trucha . Consumption of aquatic Odonata nymphs, however, arises as one of potential key mechanism for resilience of native food webs to salmonid invasion.

Alimentación de Gymnotus omarorum (Gymnotiformes: Gymnotidae) en Laguna Blanca (Parque Nacional Río Pilcomayo), Formosa, Argentina

Diet of the electric knife-fishes, Gymnotus omarorum, is described in Laguna Blanca Río Pilcomayo National Park, Formosa province. Samples were collected monthly from September 2012 to July 2013. For the analysis of stomach contents, frequency methods, volume fraction, percentage and numerical abundance index (AI) were used. Preys ingested generally belong to invertebrates and fish that live under the floating plants. The specimens of smaller sizes to 200 mm total length (TL) had a carnivorous diet with greater specialization, while in larger sizes from 201 mm TL, was carnivorous diet of the generalist type. Increased consumption of fish and decapods with increasing LT was observed. Insects in general and in particular Odonata nymphs, dominate in small and medium sizes. Significant differences were observed in the diet of this species throughout the period considered, correlating the same with changes in biomass of floating plants. The results allow characterizing the diet of Gymnotus omarorum as a generalist.

Regulated small rivers as ‘nursery’ areas for invasive largemouth bassMicropterus salmoidesin Iberian waters

ABSTRACTFew studies have assessed the ecological role of regulated small rivers in the environmental biology of invasive largemouth bassMicropterus salmoidesin Iberian waters.Size structure, diet, physical condition, and developmental stress of largemouth bass populations were compared between two contrasting habitats in the Iberian Peninsula, the Encinarejo Reservoir and the small River Jándula below the dam (Guadalquivir River Basin, southern Spain).Size structure differed between river and reservoir populations of small (<180 mm FL) largemouth bass, with a higher proportion of individuals between 30 and 60 mm in the river and a higher proportion of 20–40 mm individuals in the reservoir. In the river, the most important prey for small largemouth bass were Ephemeroptera, Plecoptera and Odonata nymphs. In the reservoir, Gerridae insects and pumpkinseedLepomis gibbosuswere the most important prey in terms of ingested biomass for small largemouth bass, whereas large individuals consumed high percentages of common carpCyprinus carpioand pumpkinseed. Prey richness, trophic niche breadth, and trophic diversity were significantly higher in small largemouth bass from the river, as well as eviscerated mass and glucose level. Fluctuating asymmetry was lower in the river for branched rays of pectoral fins, eye diameter, and length of pectoral fins.Overall results indicate that largemouth bass are taking advantage of both habitat differentiation and flow regulation in Mediterranean streams. Therefore, regulated small rivers may play an ecological role as ‘nursery’ areas, where developmental stress is low and thus, juvenile fish can display better body condition and nutritional status than their reservoir counterparts.The present study provides information relevant to the management of largemouth bass and subsequent conservation of the valuable and endemic Iberian fish fauna. For example, size‐specific culls in the reservoirs and below the dams are suggested strategies to control the reinforcement of downstream populations.Copyright © 2013 John Wiley & Sons, Ltd.

Feeding Preferences of the Endangered Diving BeetleCybister tripunctatus orientalisGschwendtner (Coleoptera: Dytiscidae)

The numbers ofCybister tripunctatus orientalisGschwendtner diving beetles are declining in most regions of Japan, and it is included in the Red Data List of species in 34 of 47 prefectures of Japan. However, basic ecological information aboutC. tripunctatus orientalis, such as its feeding habits, remains unknown. In order to elucidate the feeding habits ofC. tripunctatus orientalislarvae, feeding preference experiments were carried out in 2nd and 3rd instar larvae. The number of Odonata nymphs consumed was significantly higher than the number of tadpoles consumed, indicating thatC. tripunctatus orientalislarvae prefer Odonata nymphs to tadpoles. In addition, all the first instar larvae ofC. tripunctatus orientalisdeveloped into second instars when they were supplied with motionless Odonata nymphs, but their survival rate was lower when they were supplied with motionless tadpoles. These results suggest thatC. tripunctatus orientalislarvae prefer insects to vertebrates.

Ontogenetic Dietary Shift in the Larvae ofCybister japonicus(Coleoptera: Dytiscidae) in Japanese Rice Fields

A number of fragmentary reports suggest that the endangered diving beetle Cybister japonicus larvae feed on tadpoles, fish, and aquatic insects. However, no quantitative study on the feeding habits of C. japonicus larvae has been reported. In this study, field observations and rearing experiments were carried out to show the feeding ecology of C. japonicus larvae. Unlike previous commentaries, the first- and second-instar larvae of C. japonicus preyed on insects, mainly Odonata nymphs and Notonecta triguttata, irrespective of prey availability, but did not eat vertebrates such as tadpoles and fish in the field. On the contrary, the third-instar larvae fed on both insects and vertebrates. Rearing experiments showed that the number of Odonata nymphs consumed was significantly more than the number of tadpoles consumed by the first and second instars but third-instar larvae ate both the Odonata nymphs and tadpoles in the tadpole-Odonata nymph mixture experiment. The total body lengths of C. japonicus new adults in the Odonata nymph and tadpole-Odonata nymph mixture treatments were statistically equal. These results suggested that the first- and second-instar larvae of C. japonicus prey mainly on insects and do not eat vertebrate animals (insectivore), whereas the third-instar larvae fed on both insects and vertebrates (generalist).

Feeding habits of the diving beetle larvae, Cybister brevis Aubé (Coleoptera: Dytiscidae) in Japanese wetlands

A number of descriptive reports suggest that Cybister larvae feed on tadpoles, fish, and aquatic insects; however, no quantitative study on their feeding habits has been reported. In order to elucidate the feeding ecology of C. brevis larvae, field observations and laboratory experiments were carried out. In the field, all C. brevis larvae fed on invertebrates, such as insects and isopoda, but did not eat vertebrates, such as fish and anuran larvae. A rearing experiment demonstrated that all C. brevis larvae provided with tadpoles died. Larvae provided with Odonata nymphs had a longer total body length than larvae reared with a mixture of tadpoles and Odonata nymphs. In addition, larvae of C. brevis could search for and eat motionless Odonata nymphs, but all larvae died from starvation when they were supplied with motionless tadpoles. These results suggested that C. brevis larvae mainly preyed upon invertebrate animals and did not eat vertebrate animals, such as tadpoles and fish.

Dietary shifts inBrycinus sadleri(Pisces: Characidae) from southern Lake Victoria

We studied the diet of Brycinus sadleri in Lake Victoria after extensive environmental changes during the 1980s. To check for diet expansion following these changes, as observed in some other fish species, we compared our results with data from the 1950s. Stomach contents were analysed in relation to fish size and time of the day to investigate ontogenetic and diel shifts in the diet.Comparison of diets before and after the environmental changes showed a shift to more generalist feeding. The main food sources in the 1950s were plants during daytime and surface insects at night. Hardly any plant material was eaten during the late 1980s, but chironomid larvae, chaoborid larvae and pupae, shrimps, Odonata nymphs and fish contributed to a broader daytime diet. These prey species were also commonly taken at night, though, like in the 1950s, surface insects accounted for the major part of the diet. We found dietary shifts during ontogeny. Juveniles fed exclusively on zooplankton. Chironomid larvae, relatively large food items in comparison with zooplankton, were the key prey of sub-adult fish. Their importance decreased in the diet of adults, which included even larger prey like shrimps, Odonata nymphs and fish. At night, surface insects replaced chironomid larvae in the diet of adult fish.Diet expansion may result from reduced competition after the decline in fish mass following the Nile perch boom. An alternative explanation, increasing the prey spectrum in response to deteriorated light conditions, is not likely to hold for B. sadleri. The ontogenetic shift to increasingly larger prey and the nocturnal shift to surface insects probably reflect optimal foraging behaviour and diel vertical migration patterns of the fish respectively. These dietary shifts emphasize the feeding flexibility of B. sadleri, which may have been essential in surviving the environmental changes in Lake Victoria.