Population changes within a group of fish species in Lake Tanganyika following their exploitation

Pelagic fish populations in Lake Tanganyika consist mainly of two small clupeid species and four centroponiid species which prey on them. Exploitation with purse-seines began in the southeast arm in 1962 and catches were sampled up to early 1969. Inshore clupeid populations were also sampled with a scoop-net (lusenga of the kind used in the traditional inshore fishery.
Clupeid biomass reached annual maxima around September. One clupeid species, Stolothrissa tanganicae Regan, dominated pelagic catches except in 2 years when about equal quantities of the other clupeid, Limnothrissa miodon Blgr. were caught. Numbers of each predator (three species of Lates and Luciolates stappersii Blgr.) decreased from 1963 to 1966 and remained low thereafter. The clupeid catch rose from 1964 to 1967 and remained high in 1968. The average nightly catch weight per year of all species together altered relatively little. Changes in population size distributions occurred.
Sampling methods were concluded to be valid for clupeid populations, but probably indi-cated only general changes in predator populations. Clupeid life-cycles are mostly accomplished within a year, and appear closely related to the periodic and spatial variations in plankton production. The two species are competitive and can replace one another in the pelagic zone. Certain distribution patterns of the clupeids and of the predator young are believed to be adaptations to severe predation. Low replacement rates under fishing pressure account for the decline of predator species, and the clupeid increase resulted from reduction in predation. A fairly stable exploited phase has apparently been reached in which clupeid biomass is much greater and predator biomass much less than in the natural state. The data encourage certain predictions. Similar major trends occurred in the much larger fishery in the Burundi sector of the lake.     

The biology of Lates species (Nile perch) in Lake Tanganyika, and the status of the pelagic fishery for Lates species and Luciolates stappersii (Blgr.)

Three Lates species, L. mariae (Stdr.), L. microlepis (Blgr.), L. angustifrons (Blgr.) and Luciolates stappersii (Blgr.) which belongs to a monotypic genus occur only in Lake Tanganyika. They are the principal predators in the pelagic and benthic fish communities. Data are presented on distribution, growth, length-weight relationships, condition, reproduction and food in the Lates spp. After a post-larval pelagic phase, each Lates sp, spends 1 year in littoral weed. Thereafter, L. mariae adopts a benthic habitat moving into deep water, L. microlepis becomes exclusively pelagic and L. angustifrons occurs from the littoral to near the limit of the oxygenated zone. Cycles in breeding correspond with seasonal maxima in clupeid prey, and changes in growth rate within a year are probably related to physiological cycles rather than to variations in the physical environment. Salient morphological and ecological adaptations are discussed. Local abundance and vagility of Lates stocks seem related to basin morphometry and depth of the oxygenated layer. L. microlepis has most vagility. The Lates appear highly susceptible to intensive fishing by purse-seines, and have been fished-up in the southeast arm in Zambia and in the Burundi sector, where only small populations remain. With reduced predation, the clupeid biomass has increased. The change to dominance of small species may be accomplished rapidly in L. Tanganyika under such conditions of exploitation. However, the type of species successions well-known in large temperate lakes are unlikely to occur because of the high degree of specialization in these fishes. A simplified pelagic community is foreseen, consisting almost entirely of clupeids and Luciolates, in which the total fish biomass will be determined above some intensive level of fishing and from year to year by the environmental factors controlling survival of young and plank-tonic food supply. Quantitative equilibrium between the few species will be determined mainly by gear selectivity and total fishing stress, and the community may be sufficiently robust by reason of its rapid turn-over rates to permit a largely empirical approach to management.     

Recruitment control and production of market-size Oreochromis niloticus with the predator Lates niloticus L. in the Sudan

Experiments were conducted in earth ponds (242–1260m²) to evaluate the Nile perch (Lates niloticus L.) as a predator for recruitment control and the production of marketable Oreochromis niloticus L. in the Sudan. Supply of the predatory fish was maintained by induced spawning of L. niloticus brooders by raising the water level in a 1–0 ha earth pond. Lates niloticus fingerlings (7–5 cm total length) were then stocked with same size O. niloticus at the ratios 1:5, 1:10 and 1:15, Lates:Oreochromis , respectively. Over a period of 7 months Lates niloticus reduced young 50g) Oreochromis population and enhanced the production of preferred-size ( 200 g) Oreochromis. The ratio 1:5 Lates:Oreochromis was established to be the most desirable for Lates -with a total production of 0.2428 kg/m² of O. niloticus with 55.7% (by weight) at the target size averaging 287.5g. The ratios 1:10 and 1:15 produced 0.2106 and 0.2153 kg m² of O. niloticus , with 49.4% and 16.9% averaging 235.0 and 210.0 g, respectively.     

Human-induced changes in the composition of fish communities in the African Great Lakes

Summary Large natural African lakes contain unique and diverse fish faunas which have evolved within each lake in a comparatively short period of time. members of the family Cichlidae are particularly diverse, although there is strong evidence to show that the haplochromines in Lake Victoria, and possibly Lake Malawi, are monophyletic. The unique faunas in Lakes Victoria and Kyoga have been subject to perturbations from the introduction of exotic fish, and the faunas in these and other lakes have been disturbed by fishing activities and other human endeavours.Factors governing the establishment of exotic species are not clearly understood. The exotic fish must be physiologically adapted to their new environment, able to compete successfully both for habitat and for food at each stage of their life history, able to avoid predation and must have a suitable reproductive potential. Although about 50 species of fish have been introduced into African inland waters, including reservoirs, only comparatively few, in particular Nile perch (Lates niloticus), various cichlids (especially tilapias) and clupeids (Limnothrissa miodon), have been successful in establishing themselves. Those that have become established have had obvious but unquantifiable impacts on the indigenous faunas.It is difficult to differentiate between the effects of fishing and of the presence of alien fish on the fish species composition of the lakes (Witte et al., 1992). Many of the lakes were overfished before introductions were made, with a resultant decline in some species, especially the larger ones, and the virtual disappearance of others. Some lake fish faunas, such as those of Lakes Kyoga and Victoria, which have been subjected to the perturbations described above, continue to change rapidly (Ogutu-Owayo, 1990b).There is a fundamental need to collect biological information on the fish communities of African lakes for effective management, resulting not only in the conservation of unique fish faunas but also the production of sustainable fish yields for the people relying on this source of protein. This information is required before any more introductions of exotic fish are made.     

基于生物能量学模型的尖吻鲈精准投喂管理辅助决策系统构建

为提高养殖管理的信息化、智能化水平,研究基于生物能量学原理和生产养殖数据构建了精养条件下尖吻鲈(Lates calcarifer)精准投喂管理模型,并通过软件开发,构建了方便使用的精准投喂管理辅助决策系统.该系统主要功能为可预测尖吻鲈生长周期中任一时间点的生长、任一生长点的饲料需求量及养殖周期对水体排放的氮磷次生污染....     

尼罗尖吻鲈和鳜鱼染色体组型分析及比较

采用PHA、秋水仙碱腹腔或背部肌肉注射,活体培养法,以前肾为材料,低渗-空气干燥法制片,进行染色体观察,运用Micromeasure version 3.3染色体分析软件和Photoshop 7.0软件首次分析了尼罗尖吻鲈的染色体数目和核型,并同鳜鱼染色体数目和核型进行了分析比较,对今后拟采取的杂交尝试提供理论基础。结果显示：尼罗尖吻鲈染色体众数为2n=48,核型公式为2m+4sm+12st+30t,染色体臂数（NF）为54;鳜鱼染色体众数为2n=48,核型公式为6sm+12st+30t,染色体臂数（NF）亦为54;两种鱼染色体短臂上均无随体,单臂染色体较多。分析表明尼罗尖吻鲈与鳜鱼杂交成功的可能性较大。     

Changes in the feeding biology of the Nile perch, Lates niloticus (L.) (Pisces: Centropomidae), in Lake Victoria, East Africa since its introduction in 1960, and its impact on the native fish community of the Nyanza Gulf

Lates niloticus is not native to Lake Victoria but was introduced during or shortly before 1960. It remained relatively uncommon until 1975, when the number in the Nyanza Gulf began to increase impressively, the estimated catch rising over 100-fold between 1978 and 1982. Originally Lates was piscivorous, its diet reflecting the composition of the native fish community. The present investigation has revealed that its diet is now almost entirely comprised of Caridina nilotica , a small microphagous prawn, and juvenile Lates. Native fish species, except for the small pelagic Rastrineobola argenteus , are very rarely consumed. This change in diet is a result of the shattering impact Lates predation has had on the native fishes, which have been virtually wiped out. The original community, which was dominated by several hundred haplochromine species and the catfishes Clarias mossambicus and Bagrus docmac which preyed upon them, and included two endemic tilapiine cichlids and 38 species of non-cichlids, no longer exists. It has been replaced by a community dominated by Lates which now accounts for well over 80% of the fish biomass in the Nyanza Gulf and very nearly 100% in the study area. The only other species regularly encountered were Oreochromis niloticus , an introduced tilapiine, and Rastrineobola argenteus , a native zooplanktivore.     

An inexpensive tag for short-term studies in milkfish (Cbanos chanos Forsskal) and in seabass (Lates calcarifer Bloch)

An opercular tag for marking adult milkfish ( Chanos chanos Forsskal) and seabass ( Lates calcarifer Bloch) is described. High tag retention and relatively low mortality rates were observed in adult fish handled two to ten times during 14-to 60-day tests. The features and advantages of the tag for marking large-sized fish in short-term studies are discussed.

Zusammenfassung

Eine preiswerte Markierung für Kurzzeitstudien des Milchfisches (Chanos chanos Forsskal) und der Centropomidae (Lates calcarifer Bloch)
Eine Kiemendeckel-Markierung für adulte Milchfische (Chanos chanos Forsskal) und Centropomidae (Lates calcacifer Bloch) wird beschrieben. Sie zeichnet sich durch gute Haltbarkeit aus und verursacht relativ geringe Mortalität bei adulten Fischen, die in Versuchen von 14 bis 60 Tage Dauer 2-bis 10mal untersucht wurden. Die Eigenschaften und Vorteile dieser Markierung für große Fische in Kurzzeitstudien werden diskutiert.

Résumé

Un marquage économique pour des études de courte durée du chanidé (Chanos chanos Forsskal) et du centropomidé (Lates calcarifer Bloch)
Un marquage d'opercule pour les chanidés (Chanos chanos Forsskal) et les centropomidés (Lates calcarifer Bloch) adultes est décrit. Une bonne conservation et une mortalité relativement basse ont été observées chez des poissons adultes examinés 2 à 10 fois pendant des expériences d'une durée de 14 à 60 jours. Les caractéristiques et les avantages du marquage de poissons de grande taille pendant des expériences d'une courte durée sont discutés.     

Trophic ecology of striped bass, Morone saxatilis, in a freshwater reservoir (Lake Texoma, U.S.A.)

Many vertebrate predators consume a wide variety of prey types, depending upon availability and vulnerability. In contrast, striped bass, Morone saxatilis , that have been introduced to Lake Texoma (Oklahoma-Texas, U.S.A.) use a very limited array of fish (mostly clupeids of the genus Dorosoma ) as prey. As a large, mobile predator, M. saxatilis should be capable of capturing and consuming numerous other species of fish that are available in the reservoir. However, examination of 1845 stomachs year-around over 5 years showed that the only marked 'switching' among prey was from Dorosoma to a diet including a high percentage of insects during spring–early summer, ignoring most other fish taxa that could have served as food. Even under essentially starvation conditions in late summer of years with scarce Dorosoma, M. saxatilis in Lake Texoma did not switch to other available fish as prey. Patterns of predation by M. saxatilis are trenchantly different from place to place: very narrow prey selectivity even under starvation conditions has been reported once previously for the species in a freshwater reservoir, but in its native marine and estuarine environment and in some other reservoirs the species is more catholic in its use of prey. Why this large predator shows fidelity in some environments to particular prey, even to the extent of starvation, remains an enigma.     

The Complete Mitochondrial Genome Sequence and Characterization of Single-Nucleotide Polymorphisms in the Control Region of the Asian Seabass (Lates calcarifer)

We determined the complete mtDNA nucleotide sequence of Lates calcarifer using the shotgun sequencing method. The mitochondrial DNA (mtDNA) was 16,535 base pairs (bp) in length, and contained 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNAs, and one major noncoding control region (CR). The CR was unusually short at only 768 bp. A striking feature of the mitochondrial genome was the high G+C content (46.1%), which is among the highest in fish. The gene order was identical to that of a typical vertebrate. Phylogenetic analyses using concatenated amino acid sequences of 12 protein-coding genes of 30 fish species representing 14 suborders clearly showed Lates calcarifer was located in the cluster of fish species from the order Perciformes, supporting the traditional systematic classification. We characterized single-nucleotide polymorphisms (SNPs) in the CR by sequencing the complete CR of 25 individuals obtained from Australia and Singapore. A total of 68 SNPs were detected. Eighteen SNPs were fixed with alternative nucleotides in Australian and Singapore seabass, and these SNPs could be used for differentiating fish from the two countries.     

Genetic affinities of an introduced predator: Nile perch in Lake Victoria, East Africa

Although the introduction of Nile perch, Lates niloticus , to Lake Victoria has received intense global attention, especially in relation to its impact on endemic cichlid species and on fishery yields, fundamental information on its taxonomy and population genetics is lacking. Most importantly, the introduced fish originated from two lakes (Lakes Albert and Turkana) containing three Lates species, and it has never been entirely clear which of these became established in Lake Victoria, or indeed whether the Lake Victoria population is derived from hybridization between Lates species. In addition, genetic drift caused by the relatively small founder population (≈ 400), the initially slow population increase followed by a period of explosive population growth, and selection pressures in the new environment may have resulted in substantial genetic changes. Allozyme data indicated that the introduced Nile perch of Lake Victoria were mainly L. niloticus from Lake Albert, although maximum likelihood estimates of stock contributions (GSI) suggested the presence of L. macrophthalmus. In contrast, introduced Nile perch in adjacent smaller lakes (Lakes Kyoga and Nabugabo) appeared to be entirely L. niloticus . The effect of the introductions on allozyme diversity varied among lakes and appeared to be uncorrelated to the number of fish introduced.     

Changes in body composition and morphology of young-of-the-year gulf menhaden, Brevoortia patronus Goode, in Fourleague Bay, Louisiana

Body composition (lipid, water, protein, energy content) and metamorphosis of young-of-the-year gulf menhaden, Brevoortia patronus Goode, were examined over a yearly cycle in Fourleague Bay, Louisiana. Metamorphosis from larvae to juveniles, as indicated by the body depth to length ratio, was completed by 30 mm S.L. Analysis of the length/weight relationship indicated separate equations for larvae/postlarvae (< 30 mm S.L.) and juvenile/subadults (30–100 mm S.L.). Major body composition changes from larvae to subadult included an increase in lipid content, a corresponding increase in energy content, and a decrease in nitrogen content. Young-of-the-year gulf menhaden did not exhibit the seasonal pattern of condition factors typical of adult clupeids. There may be a shift in energy allocation away from protein growth to lipid storage associated with attainment of a larger size. Initiation of emigration may be related to lipid storage and temperature change, with higher lipid content fish migrating first. End-of-year variations in fish size and lipid storage may be related to environmental conditions, such as water temperature and salinity.     

KLEPTOPARASITISM OF SANDWICH TERNS STERNA SANDVICENSIS BY BLACK-HEADED GULLS LARUS RIDIBUNDUS

The parasitic behaviour of Black-headed Gulls in a mixed colony of terns and gulls at the Sands of Forvie on the northeast coast of Scotland is described in some detail. Food-stealing occurred with varying frequency throughout the breeding season. Less than 6% of the terns were attacked during incubation and when their chicks were a few days old, but up to 29% were attacked thereafter. At the same time the percentage of successful attacks rose from 1% or less to 6.5%.
Food items brought back to the ternery were predominantly sandeels, clupeids and gadoids. Only a small proportion of terns carrying fish shorter than 7 cm were attacked whether they were sandeels, clupeids or gadoids.
Robbing success was higher with clupeids and gadoids than with sandeels.
The effect of the Black-headed Gulls' kleptoparasitism on the Sandwich Terns' breeding success is thought to have been negligible during incubation and early chick-life, but might have influenced fledging weight and ultimately post-fledging survival.     

The food of barramundi, Lates calcarifer (Bloch), in coastal and inland waters of Van Diemen Gulf and the Gulf of Carpentaria, Australia

Examination of the diet of Lates calcarifer , based on 3684 specimens of 4–1200 mm total length (T.L.), from two localities in north Australia showed it is an opportunistic predator with an ontogenetic progression in its diet from microcrustacea to macrocrustacea to fish. The increasing importance of fish in the diet of L. calcarifer in salt water (up to 87% of food consumed) involved a dietary shift from feeding on bottom-dwelling forms to pelagic forms. There were few differences in the diet of L. calcarifer between the two localities. Cannibalism was rarely encountered in the Gulf of Carpentaria although it was significant (11–4% of the diet of L. calcarifer of 1001–1200 mm T.L.) in Van Diemen Gulf. A significant correlation between predator and prey length was found for Ariidae, Dorosomidae, Engraulidae, L. calcarifer , Mugilidae and Polynemidae. The maximum prey/predator length ratio observed was 0–61 for the dorosomid, Nematolosa erebi.     

The food and feeding habits of the Torrent frog, Amolops larutensis

The stomach contents of 661 Amolops larutensis (Blgr.) showed that this frog feeds on a wide range of terrestrial and aquatic animals of which insects form the greater part. Feeding was confined to the rocks and vegetation bordering the water-falls. Although adult frogs were capable of ingesting large prey up to a maximum length of 47.0 mm, they showed a definite preference for prey animals within the size-range of 1 to 6.5 mm length. No clear seasonal variation in the diet was found and it was suggested that the monthly fluctuations in the amount and type of prey ingested depend largely on the activity of the prey.     

Population estimation in the Torrent frog, Amolops lamtensis (Anura: Ranidae)

The results of four attempts at yearly intervals to estimate populations of Amolops lamtensis (Blgr.) along 360 m of forest stream are discussed and the most consistent estimates are obtained using Jolly's (1965) method of analysing such data. Observations of movement within the population indicate that most frogs are recaptured close to the original point of capture although a few show considerable downstream movement, possibly as a result of being swept away by the current. The recapture expectations are not, however, random and there is a strong indication that larger frogs are more liable to recapture. There is also evidence that frogs are available for recapture for different lengths of time, and it is likely that this leads to an under-estimate of the total population.     

The fish fauna changes and the place of clupeids in Lake Kainji,Nigeria

The fish fauna changes and the place of the clupeids was examined. It was found that the conditions in the lake since impoundment have favoured the growth and development of these little sardines. The studies undertaken prior to impoundment and their continuation right from the time of the closure of Kainji Dam in August 1968 has made it possible for these changes to be followed sequentially.     

Molecular cloning and sequencing of Australian black bream Acanthopagrus butcheri and barramundi Lates calcarifer fish growth hormone cDNA using polymerase chain reaction.

The complementary DNA (cDNA) encoding the preprotein growth hormone (pre-GH) from two Australian marine fish species, namely Acanthopagrus butcheri and Lates calcarifer, have been isolated, cloned and sequenced. The sequences were amplified from reverse transcribed total RNA of whole brains using Polymerase Chain Reaction (PCR) and oligonucleotide primers corresponding to the 5' and 3' regions of Pagrus major. Use of PCR offers a rapid method of isolating fish GH cDNA sequences for commercial and taxonomic applications. Sequence comparison indicates a high degree of conservation for GH cDNAs within the family Sparidae.     

Changes in the prey ingested and the variations in the Nile perch and other fish stocks of Lake Kyoga and the northern waters of Lake Victoria (Uganda)

The fish stocks of Lakes Kyoga and Victoria have changed since Nile perch, Lates niloticus (L.), was introduced, and this is reflected in the prey ingested by the predator. Initially, haplochromine cichlids constituted the main prey of most sizes of Nile perch. As the stocks of these have declined, Caridina nilotica (Roux) and Anisopteran nymphs have become the dominant food of the juveniles, while Rastrineobola argentea (Pellegrin), juvenile Nile perch and Oreochromis niloticus (L.) have become the main food of larger Nile perch. Apart from R. argentea , most of the native fish species of these lakes have disappeared. The stocks of Nile perch in Lake Kyoga, to which it was introduced earlier than to Lake Victoria, have declined after dominating the fishery since 1965. and have been superseded by O. niloricus . an introduced herbivore. Similar changes are now occurring in Lake Victoria. The Nile perch might not maintain the high yield realized in the two lakes when haplochromines were abundant. It is therefore necessary to exercise caution with high and long-term investments aimed specifically at developing the Nile perch fishery.     

A robust flow-cytometric protocol for assessing growth rate of hatchery-reared barramundi Lates calcarifer larvae

In this study, a flow-cytometric cell cycle analysis method to assess instantaneous growth rate of whole larvae of the Australian barramundi Lates calcarifer was developed and validated. High-resolution DNA measurements of either fresh, frozen or RNAlater-preserved larvae (gap0-gap1, G(0) -G(1), coefficient of variation (c.v.) < 3, 4 and 5%, respectively) enabled the deconvolution of the DNA histogram and assignment of the proportion of nuclei into cell cycle compartments G(0) -G(1), S (DNA synthesis) and G(2) -M (Gap2-Mitosis). This technique can be also used for individual fish tissues such as brain, liver, fin and muscle. For the first time, the combined proportion of replicating nuclei (into S and G(2) -M phases) of whole fish larvae and absolute growth rate in length (mm day(-1)) has been correlated in commercial aquaculture conditions. Fast growing L. calcarifer larvae had an overall hyperplasia advantage as indicated by a greater proportion of cells in the S+G(2) -M phase compared with slow growing larvae, which might explain the increasing differences in size during culture. In a fasting trial, larvae ceased growth while maintaining the constant initial rates of cell division throughout a 6 day period. For a highly fed fast growing control group, cell division rates significantly increased after day 4. Flow-cytometric cell cycle analysis of whole fish larvae may provide fish biologists and aquaculturists with a better understanding of how cell division rates influence early growth in natural and artificial environments.