Effects of Nile perch (Lates niloticus) introduction into Lake Victoria,East Africa,on the diet of Pied Kingfishers (Ceryle rudis)

In recent years the ichthyofauna of Lake Victoria, the world's largest tropical lake, has gone through dramatic changes. The population of Nile perch, a large predator which has been introduced into the lake by man, increased explosively at the expense of many haplochromine cichlid species. At the same time, numbers of a small cyprinid (dagaa) rose sharply.

Previously Pied Kingfishers on Lake Victoria fed mainly on haplochromines. Only the youngest nestlings depended on dagaa as primary food. The current diet of adult birds clearly reflects the changes which have occurred in the fish community. Pellet analysis reveals a shift towards a diet composed of almost 100% dagaa.

The change in prey species composition has increased the number of fish a kingfisher needs to catch daily in order to meet its energetic demands, because:

1. (1)

   the mean size of haplochromines is larger than that of dagaa;

2. (2)

   (2) the mean size of dagaa has decreased since the increase in Nile perch;

3. (3)

   (3) the weight of dagaa is lower than that of haplochromines of equal size;

4. (4)

   (4) mainly juvenile dagaa and adults in poor condition are accessible to kingfishers.

     

Food niche segregation between the Malachite Kingfisher,Alcedo cristata,and the Pied Kingfisher,Ceryle rudis,at Lake Nokoué, Bénin

Several species of kingfisher occur on Lake Nokoué, southern Bénin, including Malachite (Alcedo cristata) and Pied Kingfishers (Ceryle rudis). Here, we compare their diet and estimate the degree of overlap in food niche by analysing contents of regurgitated pellets collected near nesting sites of Pied Kingfishers or inside the nest chambers of Malachite Kingfishers. Characteristic fish skull bones were identified using a reference collection of local fish skeletons. Malachite Kingfishers feed most frequently on fish that occur around floating vegetation, mainly Kribia sp. (56%), Hemichromis fasciatus (28%) and Sarotherodon melanotheron (8%). Important differences were found between different pairs, and between adults and nestlings, the latter being fed almost exclusively on Kribia sp. Larger fish are fed to nestlings than are eaten by the adults. Pied Kingfishers prey upon 14 different fish species, some of them being caught in the pelagic region of the lake, particularly clupeids taken by hovering. By comparison with Malachite Kingfishers, Pied Kingfishers feed on a wider diversity of prey, and take larger fish, so that the dietary overlap between the species is relatively low (O = 0.181).     

Shifts in the food of Nile tilapia, Oreochromis niloticus (L.) in Lake Victoria, Kenya

Studies of the food of introduced Nile tilapia, Oreochromis niloticus (L.) with respect to size, habitat and season were conducted between November 1998 and October 2000 in Kenyan waters of Lake Victoria. Stomach contents of 1980 specimens collected by demersal trawl and seining were analysed. Nile tilapia originally known to be herbivorous, feeding mostly on algae has diversified its diet to include insects, fish, algae and plant materials. The major diet of fish <5 cm total length was zooplankton whereas bigger fish included a wider range of food items in their diet. There was spatial variation in diet with insects and algae dominating in the gulf and open water habitats respectively. There was no seasonal variation in the food items ingested and diel feeding regime indicated that O. niloticus is a diurnal feeder. The shift in diet could be due to ecological and environmental changes in Lake Victoria, which have been associated with changes in composition and diversity of fish and invertebrate fauna, emergence and dominance of different flora including water hyacinth Eichhornia crassipes (Mart.) Solms‐Laub., and algae communities. The feeding habit of O. niloticus is discussed in the context of changes occurring in the lake.     

Feeding habits and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in a shallow lake,central China

The diet and predator‐prey size relationships of mandarin fish Siniperca chuatsi (Basilewsky) in Lake Xiaosihai along the middle reach of the Yangtze River were studied through stomach content analysis. A total of 401 specimens (91–539 mm total length) were collected in 2007. The diet was dominated by topmouth gudgeon Pseudorasbora parva, sharpbelly Hemiculter leucisculus, redfin culter Cultrichthys erythropterus, and crucian carp Carassius auratus, with significant seasonal and ontogenetic differences. Ontogenetic variation in diet was apparent that larger prey items such as crucian carp and redfin culter became more common, while smaller prey such as topmouth gudgeon, bitterlings and shrimps gradually declined in the larger fish. Mandarin fish total length (TL) was strongly related to mouth gape width (GW) and gape height (GH). Mandarin fish TL and prey fish TL as well as mandarin fish GW and prey fish body depth (BD) were positively and linearly related for sharpbelly, redfin culter and crucian carp. Strong size selectivity for topmouth gudgeon, sharpbelly and redfin culter as prey indicated that the piscivorous mandarin fish can have potential impact on the population size structure of the three prey fish.     

Seasonal diet and amphipod size selection of juvenile common bully, <Emphasis Type="Italic">Gobiomorphus cotidianus</Emphasis>, in a coastal New Zealand lake

We examined the seasonal diet of juvenile (≤32 mm total length) common bullies, Gobiomorphus cotidianus, in Lake Waihola, South Island, New Zealand and whether they preyed selectively on the amphipod, Paracalliope fluviatilis, which was a dominant prey item. Generally, ≥75% of all fish sampled had consumed amphipods, which comprised 80%, or more, of the total prey volumes in fish stomachs over most of a year except on one sampling occasion. Copepods, snails, chironomids, Daphnia, mysids and isopods also contributed to the diet. Comparisons of the size distribution of amphipods in fish stomachs and the lake on the date of sampling showed that on four occasions, juvenile bullies selectively consumed small amphipods. No selective feeding was detected on the other occasions. The dominance of primarily benthic amphipods in the diet of juvenile bullies which, in turn, are preyed on by piscivores, suggests a strong benthic-pelagic link in the transfer of energy in Lake Waihola. Handling editor: J. Cambray     

5. LIVINGSTONE IN NORTH-EASTERN RHODESIA

Sugg, M. St. J. 1974. Mensural and moult data from a breeding colony of Pied Kingfishers. Ostrich 45: 227–234.

Pied Kingfishers were ringed over two breeding seasons at a breeding colony on the Kenyan shore of Lake Victoria. Data were collected on weight, wing and bill length, injury and moult. Bill abrasion and breakage from nest excavation was found in both sexes and regeneration of worn and broken bills was recorded.

Adult birds of both sexes returned to the colony to breed but no juvenile was recaptured the year after hatching. Females are slightly larger than males (wing length) and both sexes showed a weight increase in the evening prior to roosting. Juveniles had shorter wings and bills than adults but their weights were similar. Their bills were short, soft, weak and the gape was salmon pink. No juveniles showed any moult. Adult moult records support the sequence and duration of moult suggested by Douthwaite (1971) though no overall decrease of moult activity was recorded during the breeding season.     

ON THE RACE OF CARDINAL WOODPECKER Dendropicos fuscescens (Vieillot) OCCURRING IN THE EASTERN TRANSVAAL

Summary

Hustler, K. &; Marshall, B.E. 1996. The abundance and food consumption of piscivorous birds on Lake Kariba, Zimbabwe-Zambia. Ostrich 67:23-32.

About 40 species of piscivorous birds have been recorded on Lake Kariba (Zimbabwe-Zambia) but only 26 were observed during this study, carried out in 1986–87. The Reed Cormorant Phalacrocorax africanus was the most numerous and made up 51.4% of all the birds seen, followed by the Whitewinged Black Tern Chlidonias leucoptera (26.7%), and the Darter Anhinga melanogaster (10.8%). Several species roosted or bred in the drowned trees which project above the lake surface but gently sloping shores were the most important feeding grounds. Relatively few birds were seen on steeply sloping shores or in open water. There was a distinct pattern of seasonal abundance, with birds being most numerous in the rainy season (November-April). The relative abundance of some fish species also was greatest during this period. There was a positive relationship between the numbers of some bird species and the relative abundance of these fish. The mean density of piscivores (0.05 ha^?1) was low compared to some other African waters. This is attributed to the fact that Lake Kariba is relatively deep and its shoreline is mostly steep. The mean population of 25 000 birds consumed less than 1000 t of fish per annum, compared to almost 40000 t taken by the commercial fisheries. A considerable portion of the birds' diet was fish that were not taken commercially.     

UTILIZATION OF PLANT MATERIALS BY JUVENILE AFRICAN CATFISH (CLARIAS GARIEPINUS) AND ITS IMPORTANCE IN FISH CULTURE

SUMMARY

Juvenile African catfish Clarias gariepinus between 100 and 200 mm total length from Lake McIlwaine, Zimbabwe are able to digest plant proteins. The digestibility of three major plant proteins (maize, sunflower seed and soya meal) was 30,0, 65,4 and 84,3% respectively. C. gariepinus excreted between 27 and 55% of its soluble nitrogen as urea. Fats from one diet were found to spare proteins and to be 73% utilized.

The basal metabolic rate of juvenile catfish may be represented by the general formula:

BM = 2,56 - 0,40 (In W) - 0,10 (In W) (FS)

where BM is the basal metabolic rate in cal g_?1 h_?1, W is the mass in grams and FS is the feeding state (expressed as zero for a feeding fish and one for a fasting fish).

The metabolism of starving, fasting, feeding, and stressed active juvenile fish was found to be approximately 0,28, 0,56, 1,23 and 4,5 cal. g_1 h_1 respectively.

World protein shortages and the contribution that fish culture can make are discussed. Sample calculations show catfish lose up to 38% of ingested plant protein while direct consumption of vegetative material by humans results in a loss of 33% of the protein due to imbalances in amino acid make-up of plants. It is generally not physically possible to eat the quantities of traditional low protein plant material needed to obtain the necessary protein. Therefore the use of more concentrated and more digestable animal protein is necessary, and catfish with dry weight ptotein levels of 70 to 80%, are capable of acting as protein concentrators.     

Management of the Nile perch, Lates niloticus fishery in Lake Victoria in light of the changes in its life history characteristics

Nile perch was introduced into lakes Victoria and Kyoga in the 1950s and 1960s from Lake Albert. The changes in prey eaten and the life history characteristics of Nile perch in lakes Victoria and Kyoga from the 1960s to 1990s were examined and compared with Lake Albert. The dominant prey eaten changed from haplochromines, Caridina nilotica, Rastrineobola argentea, and Nile perch juveniles. The condition factor deteriorated from 1.4 in 1960s to 1.2 in 1990s, compared with 1.3 in Lake Albert suggesting a reduction in food supply. Therefore, exploitation of Nile perch prey should be controlled. The size at first maturity increased from 30–40 to 40–50 cm and 50–59 to 80–100 cm for males and females, which is similar to Lake Albert. Sex ratios decreased from 85–100 to 20–65 females for every 100 males suggesting that Nile perch had less capacity to replenish its stocks such that breeding females should be protected. As males mature at 50–55 cm and females at 80–100 cm, immature males of <50 cm and breeding females of >100 cm could be protected through size selective exploitation of fish of 50–100 cm using gillnets of 127–254 mm.     

Growth and contribution of stocked channel catfish,Ictalurus punctatus (Rafinesque, 1818): the importance of measuring post‐stocking performance

In this study it was sought to quantify post‐stocking growth, survival, and contribution of advanced size (178 mm total length [TL]) channel catfish Ictalurus punctatus fingerlings, something rarely done. Channel catfish populations were evaluated before (May 2010) and after (May to August 2011 and 2012) stocking. Relative abundance, stocking contribution, and growth were different (P < 0.05) in the two study impoundments (lakes Lone Chimney and Greenleaf, Oklahoma). For fish stocked in Lake Lone Chimney, stocking contribution was lower (3–35%), and average length and weight of stocked fish by age‐2 reached 230 mm TL and 85 g, whereas the stocking contribution (84–98%) and growth in length (340 mm TL) and weight (280 g) were higher by age‐2 in Lake Greenleaf. Given these unambiguous differences of post‐stocking performance, benchmark metrics that represent population‐level information such as relative abundance and average length and weight of the sample masked these significant differences, highlighting the importance of marking hatchery‐fish and then following them through time to determine the effectiveness of stocking. These results suggest that stock enhancement programmes would benefit from studies that quantify post‐stocking performance of hatchery fish.     

Utilization of the exotic cladoceran Daphnia lumholtzi by juvenile fishes in an Illinois River floodplain lake

Daphnia lumholtzi comprises a substantial component of the zooplankton community during mid‐ to late‐summer in Lake Chautauqua, a floodplain lake along the Illinois River near Havana, Illinois. In order to quantify the utilization of D. lumholtzi by juvenile fishes, diet analyses were conducted for seven juvenile fish species collected from Lake Chautauqua during the 2001 annual drawdown period. Freshwater drum Aplodinotus grunniens and emerald shiner Notropis atherinoides demonstrated negative selectivity for D. lumholtzi relative to native zooplankton species whereas four species of fish (bluegill Lepomis macrochirus, white bass Morone chrysops, white crappie Pomoxis annularis and black crappie Pomoxis nigromaculatus) consumed substantial amounts of D. lumholtzi. Although selectivity values for D. lumholtzi varied among these fish species, positive selection for D. lumholtzi increased similarly among larger size classes of each fish species, and corresponded with ontogenetic shifts in diet. Mean body length of D. lumholtzi consumed by 20–69 mm L_T juvenile fishes ranged from 0·75 to 0·99 mm with a calculated total length range of 2·0–2·6 mm. Results from this study provide evidence that high abundances of D. lumholtzi in mid‐ to late‐summer provide an additional food source for several juvenile fish species during a time when abundances of large native cladoceran species (i.e. Daphnia) are low, and juvenile fishes are searching for larger prey associated with ontogenetic shifts from zooplankton to macroinvertebrates and fishes. Because zooplankton production is typically lower in rivers than in lakes, survivorship of juvenile fishes produced in floodplain lakes may be higher in riverine systems if they are not reliant on zooplankton as a primary food resource. Therefore, high abundances of D. lumholtzi may benefit juvenile fishes in managed floodplain lakes, such as Lake Chautauqua, by increasing growth and facilitating the transition from zooplanktivory to insectivory or piscivory.     

Cytological and morphological ontogenesis and involution of the thymus in cichlid fishes (Cichlidae,Teleostei)

The ontogenesis and involution of thymus in cichlid fishes was studied with the aim of comparing development in the bottom-spawning species Tilapia zillii and T. tholloni, and in the mouth-brooding species Oreochromis auratus, O. niloticus, O. mossambicus, and Sarotherodon galilaeus. For comparison, data are also given on bottom-spawning Cichlasoma spp. from America and mouth-brooding Pseudotropheus auratus and Aulonocara nyassae from Africa. Developmental changes were followed histologically by means of light and electron microscopy of sections, beginning with embryos 24 h after fertilization, up to 14-year-old specimens of O. auratus. In all these fish, the anlagen of the thymus glands begins from the third and fourth gill pouches, and their development shows a high correlation with the pace of general organogenesis, which differs greatly in the bottom-spawning and mouth-brooding cichlids. In juveniles of bottom-spawners of 20–40 mm total length and in mouth-brooders of 40–60 mm total length, three cell types are present in the thymus: thymocytes, with large, dense nuclei; epitheliocytes, with long cell extensions containing bundles of tonofibrils; and reticulocytes, with short, granulated cell extensions. Hassall's corpuscles start to develop in larvae of T. zillii at 20–35 mm total length, and in specimens of 40 mm and more total length the corpuscles are typical, formed by inner and outer rings of epitheliocytes. At 30–45 mm total length, cell debris starts to accumulate in the interior of the corpuscles as an early sign of regression. As involution continues, macrophages accummulate within and around the Hassall's corpuscles. The epitheliocyte rings are eventually completely broken down. Isles of thymocytes persist in tilapias from the age of 1–14 years, but most of the thymus volume is occupied by blood lacunae and pigmented macrophage aggregations. The morphology is similar in the mouth-brooding species Pseudotropheus beginning at 1.5 years of age. © 1995 Wiley-Liss, Inc.     

A New Species of Kudoa (Myxosporidea: Chloromyxidae) from the Spot,Leiostomus xanthurus Lacépède,in Clear Lake,Texas*

SYNOPSIS. Kudoa branchiata sp. n. (Myxosporidea: Chloromyxidae) is described from the gills of the marine sciaenid fish, Leiostomus xanthurus Lacépède, from Clear Lake, Texas. Twelve of the 429 hosts examined from 10 September 1970 to 28 April 1971, were infected. Eight of the 12 infected fish were collected in February and March 1971—a period during which only 13% of the total host sample was taken. The mean total length of infected hosts was 149 mm, with a range of 112–185 mm. The mean number of myxosporidean cysts per infected host was 3.5, with a range of 1–11.     

The food and feeding habits of blackspot snapper, Lutjanus fulviflamma (Pisces: Lutjanidae) in shallow waters of Mafia Island, Tanzania

Natural diet and feeding habits of blackspot snapper, Lutjanus fulviflamma (Forsskål 1775) were investigated in Mafia Island Marine Park (MIMP) and intensively fished areas (IFA) between May 1999 and April 2001. An index of relative importance (IRI) was used to assess the food preference for L. fulviflamma. Feeding habits were studied with respect to sex and size of the predator, seasons and feeding periodicity. Of 4642 L. fulviflamma specimens sampled, 46% had empty stomachs. Brachyurans were the main prey of L. fulviflamma accounting for 48% IRI. Benthic invertebrates dominated by other crustaceans, gastropods, bivalves, cephalopods and polychaetes and demersal teleosts made up the remainder of the diet. Female and male L. fulviflamma were not effectively segregated by trophic dimension in the study areas. Specimens in the 90–120 mm total length (TL) fed exclusively on crustaceans, with shrimps accounting for 40% IRI. Lutjanus fulviflamma in the 270–300 mm TL preferred fish prey accounting for 50% IRI. The diet of fish species showed clear spatial differences, which were dependent on size distributions. Lutjanus fulviflamma fed mostly but not exclusively at night peaking at dusk and dawn. The results clearly demonstrate that L. fulviflamma is an opportunistic forager, which exhibits both diel and ontogenetic feeding habits.     

Diet composition,feed preferences and mouth morphology of early stage silver therapon (Leiopotherapon plumbeus,Kner 1864) larvae reared in outdoor tanks

This study examined the diet composition, feeding preferences, and mouth morphology of the silver therapon (Leiopotherapon plumbeus, Kner 1864) larvae under captive conditions. Larvae were reared in outdoor tanks (4 m³) with natural food grown 2 weeks prior to start of larval rearing. Food preference was measured by the Chesson's electivity index (α_i). Gut content analysis of larvae sampled between 5 and 25 days after hatching (DAH) showed the dominance in the diet by zooplankton, mainly copepod nauplii, cladocerans and insect larvae. Small fish larvae (5–9 DAH; 3.32–6.29 mm standard length) preferred cladocerans, ciliates and copepod nauplii; whereas older larvae (12–25 DAH; 5.45–19.26 mm standard length) preferred insect larvae over cladocerans and adult insects. The mouth gape size at 5 DAH was 359 μm and increased to 3.75 mm at 40 DAH when body size grew at an average rate of 0.59 mm d^?1. The standard length (SL) of L. plumbeus larvae was strongly associated with mouth size (r² = 0.98, P < 0.05), indicating a progressive increase of ingested prey size of the fish larvae. These results clarified the early life feeding ecology of this species, which is essential in developing effective hatchery techniques.     

Length–weight relationships of two sympatric species (Knipowitschia byblisia Ahnelt, 2011 and K. caunosi Ahnelt, 2011) in Köycegiz Lake,Turkey

This study provides basic information on length–weight relationships for Knipowitschia byblisia Ahnelt, 2011 and Knipowitschia caunosi Ahnelt, 2011, two endemic species of Köycegiz Lake Basin (Southern‐West of Turkey). Samplings were carried out seasonally from 2014 to 2015 by means of beach seine nets with mesh sizes from 10 to 35 mm. A total of 343 individuals from the two fish species were examined, with more specimens belonging to K. byblisa (90.4%). The total length–weight relationships were calculated as: W = 0.0054 TL^3.384for K. byblisia and W = 0.0058 TL^3.417for K. caunosi, respectively.     

Scaling effects on the neuromuscular system,twitch kinetics and morphometrics of the cod,Gadus morhua

Size related changes in muscle twitch kinetics, morphometrics and innervation have been examined in cod, Gadus morhua. Fish size ranged from 9 cm to 45 cm in total length (L).

Twitch contraction time (time to 90% relaxation), scaled in proportion to L^0.29. Scaling of morphometric parameters was essentially geometric. Mean cross‐sectional area and weight of the myotomal muscle scaled in proportion to L^2.05 and L^3.08 respectively. These results are discussed in the light of alterations in length specific swimming performance and kinematics as fish grow.

During growth, the number of endplates terminating on each fast fibre increased, from around 10 on fibres 2 mm in length (～10 cm fish) to 20 on 10 mm fibres (—40 cm fish). However, mean spacing between endplates increased from around 0.25 mm to 0.50 mm. The functional significance of polyneuronal innervation in teleost fast muscle fibres is discussed.     

Anadromous trout threatened by whitefish gill‐net fisheries in the northern Baltic Sea

We estimated the effect of the gill‐net fisheries targeted at whitefish (Coregonus sp.) on anadromous sea trout, Salmo trutta, in the Gulf of Bothnia, Baltic Sea using separate data for fish species. The analysis of sea trout captures was based on tagging and recapture data collected in 1998–2011, while whitefish data were derived from individual samples of commercial fisheries from the same period. The mesh sizes used in gill‐net fishing and the seasonal and temporal distributions of recaptured sea trout and sampled whitefish were compared in the northern and southern Gulf of Bothnia. The trout had typically spent 1–2 years at sea, and they were mainly immature with a median body length of 40–43 cm at the time of recapture in gill nets. Despite the increase in the minimum permitted landing size from 40 to 50 cm in 2008, the median length of recaptured trout remained unchanged during the study period. Most (59%) of the gillnetted trout were caught in the southern Gulf of Bothnia in gill nets with mesh sizes of 40–45 mm, which were also used in the whitefish fishery (72%). In the northern Gulf of Bothnia, nets with a smaller mesh size of 25–39 mm took 83% of the whitefish catch and 39% from recaptured trout. In both areas, the overlap in mesh sizes used to gill‐net catch whitefish and sea trout increased during the study period. There were clear seasonal and areal differences in the relative probability of sea trout being captured in gill nets, suggesting that carefully tailored spatial and temporal restrictions on gill‐net fisheries could provide a tool to protect young sea trout without causing intolerable difficulties for the fisheries targeting other species.     

Effect of Ligula intestinalis on the reproductive capacity of Rastrineobola argentea in Lake Victoria

This study examined the potential effect of the cestode Ligula intestinalis on the reproduction of the indigenous cyprinid Rastrineobola argentea in Lake Victoria. Ligula intestinalis had a marked effect on the breeding cycle of R. argentea. The proportion of the infected population in advanced stages of maturation prior to spawning was considerably reduced compared with uninfected fish. Infection by L. intestinalis significantly reduced the fecundity of individual fish, particularly in the 45–60 mm size range; the component of the population that makes the greatest contribution to reproductive output. The reduction in reproductive output of the R. argentea population could potentially affect replenishment of stocks in this important fishery.     

Some biological aspects and life history strategies of Nile tilapia Oreochromis niloticus (L.) in Lake Victoria, Kenya

The life history characteristics of introduced Nile tilapia (Oreochromis niloticus L.) in Lake Victoria, including, sex ratio, fecundity, reproduction, weight‐length relationship and body condition were studied and compared with those of other populations. Samples were collected by trawling and seining in the Kenyan sector of Lake Victoria between June 1998 and December 2000. Males predominated over females (sex ratio 1.42 : 1 : 00). O. niloticus spawned throughout the year but with a peak between December and June. Length at first maturity was (mean ± SD) 30.81 ± 0.09 for females and 34.5 ± 6 0.48 for males. There was little seasonal variation in relative condition, which ranged from 0.92 to 1.05 in males and 0.94 to 1.07 in females. Gonadosomatic index (GSI) was low during the postspawning period (July to October) and high during the protracted breeding period (December and June). Fecundity ranged from 905 to 7619 oocytes for fish of 28 to 51 cm total length (TL) respectively. The relationships between fecundity (F) and total length (L), weight (W) and ovary weight (OW) were: F = 8.159L^1.53, F = 96.269W^0.4504, F = 1806 + 39.4OW. The slope b of the weight‐length relationship was 3.08–3.32 for males and 3.07–3.22 for females. Growth was allometric in both cases and was significantly different from the expected value of 3. The life history strategy of O. niloticus is discussed in context of environmental changes occurring in the lake.