Fish fauna destruction after the introduction of a non-native predator (Cichla kelberi) in a Neotropical reservoir

In South America, the introduction of peacock-bass (Cichla), a voracious predator fish, has been an underestimated threat for native fish communities. Although this predator is widespread in many reservoirs, few studies have explored its impact on biodiversity. To investigate the relationship between invasion and fish diversity, the present study followed a natural experiment in the Rosana Reservoir (Paraná River basin), where Cichla kelberi were introduced in 2004. We monitored fish assemblages associated with submerged macrophytes between 2003 and 2007, using a 1 m² throw trap. In the years following the introduction, fish diversity dramatically changed. For example, in March 2007, mean fish density and richness were reduced by ca. 95 and 80%, respectively, and many small-sized species had vanished. One aspect was the gradual change of biodiversity, which unfolded at two times during each year: (1) impacts during summer/autumn periods, which coincided with large shoals of young C. kelberi in the patches; and (2) assemblage recovery during the spring. The sequence of extinction-colonization events, however, might not be able to maintain fish assemblages due to the decrease in recovery intensity each spring; assuming a constant decline rate in the coming years, we predict complete assemblage extinction by the summer of 2010. Results from this natural experiment provided evidence supporting the collapse of fish assemblages soon after the introduction of C. kelberi. Such rapid destruction (2 years) reveals an important homogenizing force behind this predator and stresses the need for control measures that prevent new transferences among South American basins.     

Innate sound production in the cichlid Oreochromis niloticus

The mouthbrooding cichlid Oreochromis niloticus is one of the world's best-studied fish and is raised extensively for aquaculture. Although it is a common behavioural model, its acoustic communication has been neglected. Because of extensive parental care, the species is a good candidate for vocal learning. In male O. niloticus , we investigated for the first time sound production in agonistic interactions during nest construction. Males produce short-duration (250–400 ms), often double-pulse sounds. Most energy is below 200 Hz and includes three main low-frequency peaks although energy extends beyond 1 kHz. Males (separated as eggs and raised in isolation) produce similar sounds in the same context as parental fish, indicating that the ability to produce sounds and the basic properties of the sounds are innate.     

Spatial-temporal distribution of preimaginal blackflies in Neotropical streams

The current study investigates the spatial-temporal distribution of preimaginal blackflies in three a priori established, adjacent areas of Brazil and Venezuela. First we tested the hypothesis that the distribution of individual simuliid species, over two geographic scales, were predictable on the basis of several habitat parameters. Secondly, we determined if local species assemblages remain constant over two spatial axes, i.e., were species assemblages predictable within and between defined regions. Finally we compared the species assemblage between Venezuelan streams sampled in both the wet (October) and dry (February) seasons. As stream conditions changed across a north–south gradient, so did the occurrence of the most common species. This change in species composition from upland to lowland areas is consistent with the patterns of faunal change seen in North American simuliid assemblages. Discriminant Function Analysis showed a strong association between regional demarcations and stream site conditions. These results were paralleled by the strong correspondence between species assemblages and these regions. Thus each region presented both distinct stream environments and species assemblages. Monte Carlo analysis suggests that some if not all species are not only present in both the wet and dry season but that they are continuing to use the same stream sites. Three broad contingent rules for blackfly species assemblages in new world streams are put forward; (i) the ubiquitous nature of simuliids; (ii) species often distribute themselves along an axis of stream size and; (iii) there is a strong and consistent correspondence between regional characteristics of streams and the species assemblage.     

Life history of an invasive and unexploited population of Nile tilapia (Oreochromis niloticus) and geographical variation across its native and non-native ranges

Although the life history traits of Nile tilapia, Oreochromis niloticus have been studied since the early 20^th century, the potential range of life history parameters in unexploited populations and geographical variability in life history traits are still poorly understood. We explored life history traits (age composition, growth rate, mortality, size, and age at maturity) of an invasive and unexploited population in the Tabaru River, Yonaguni-jima Island, southwestern Japan, through comparisons with exploited populations across the species’ global distribution. Analysis of sectioned otoliths from 307 fish revealed that growth and maximum age were sexually dimorphic (females growing less but having greater longevity). Large-scale comparisons with exploited populations revealed that the unexploited Tabaru River population had a greater life span than exploited populations in other regions, but the growth rate was in the middle of the range of observed values. Although a high variation in life history parameters was observed among populations (L _∞, K, maximum age), we found no significant variation in life history traits by latitude or between African and non-African populations. Such a combination of long life span and high variability in life history traits in response to environmental and fishing pressures may aid the success of non-native Nile tilapia in various environments.     

Ultrastructure of otolith increments and checks in the teleost fish Oreochromis niloticus

An otolith increment is composed of an incremental zone and a discontinous zone. Observation of the otoliths of Oreochromis niloticus with transmission and scanning electron microscopy reveals that organic fibers are concentrated in the discontinuous zone and are relatively scarce in the incremental zone. On the other hand, calcium carbonate crystals are chiefly packed in the incremental zone and are less dense in the discontinuous zone. Both fibers and crystals are oriented perpendicular to the growth increments. Otolith checks, or discontinuities, contain even denser fibers and fewer fine crystals than does the discontinuous zone. A higher proportion of individual fibers is prominently stained in the discontinuous zone and check than in the incremental zone. Other features of individual fibers appear to be the same among the three zones. The crystals on either side of a check or a discontinuous zone resemble each other both in size and orientation. Zonation of protein and mineral components of otoliths can be understood in terms of both incremental growth and the daily cycle of deposition.     

Initiation of gynogenesis in Oreochromis niloticus following heterologous fertilization

Fertilization of tilapia ( Oreochromis niloticus ) eggs with heterologous sperm from carp ( Cyprinus carpio ), and from some other eyprinids resulted in higher levels of haploid gynogenetic development than in unfertilized eggs. Normal and irradiated carp sperm achieved similar rates of activation of tilapia eggs, but lower rates than those achieved by irradiated tilapia sperm. Diploidy in gynogenetic eggs fertilized with carp sperm was restored using pressure shocks and resulted in the development of healthy tilapia gynogens.     

Fine structure of the branchial epithelium in the teleost Oreochromis niloticus

We have studied the gill epithelium of Oreochromis niloticus using transmission electron microscopy with the particular interested relationship between cell morphology and osmotic, immunoregulatory, or other non‐regulatory functions of the gill. Pavement cells covered the filament epithelium and lamellae of gills, with filament pavement cells showing distinct features from lamellar pavement cells. The superficial layer of the filament epithelium was formed by osmoregulatory elements, the columnar mitochondria‐rich, mucous and support cells, as well as by their precursors. Light mitochondria‐rich cells were located next to lamellae. They exhibited an apical crypt with microvilli and horizontal small dense rod‐like vesicles, sealed by tight junctions to pavement cells. Dark mitochondria‐rich cells had long dense rod‐like vesicles and a small apical opening sealed by tight junctions to pavement cells. The deep layer of the filament epithelium was formed by a network of undifferentiated cells, containing neuroepithelial and myoepithelial cells, macrophage and eosinophil‐like cells and their precursors, as well as precursors of mucous cells. The lateral‐basal surface was coated by myoepithelial cells and a basal lamina. The lamellar blood lacunae was lined by pillar cells and surrounded by a basal lamina and pericytes. The data presented here support the existence of two distinct types of pavement cells, mitochondria‐rich cells, and mitochondria‐rich cells precursors, a structural role for support cells, a common origin for pavement cells and support cells, a paracrine function for neuroepithelial cells in the superficial layer, and the control of the lamellar capillary base by endocrine and contractile cells. Data further suggest that the filament superficial layer is involved in gill osmoregulation, that may interact, through pale mitochondria‐rich cells, with the deep layer and lamellae, whereas the deep layer, through immune and neuroendocrine systems, acts in the regeneration and defense of the tissue. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.     

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.     

Urbanization and roads drive non-native plant invasion in the Chicago Metropolitan region

Human modification of the landscape, including urbanization and road construction, has facilitated the spread and establishment of non-native plant species. The effects of urbanization and roads are expected to be species-specific due to differences in species habitat requirements. We examined the influence of urbanization and roads on the occurrences of 16 non-native plant species in over 2000 wetlands within the Chicago metropolitan region in northeastern Illinois, USA. We found that species, or groups of species, responded differently to the effects of urbanization, roads, and proximity to conspecific populations. Occurrences of halophyte species were best predicted by road variables; halophytes were more commonly associated with major roads such as interstates and federal highways, road types that are likely to receive greater applications of de-icing salts. Several species were associated with proximity to Chicago. Proximity to Chicago may serve as a proxy for the degree of urbanization; or alternatively, may reflect a pattern of outward dispersal from an initial establishment point in the urban center. All study species were positively associated with distance to the nearest occupied wetland, implying that for each species, wetlands were more likely to be occupied if closer to other occupied sites. Our results support the need for species-specific understanding of responses to urbanization and roads to facilitate management of non-native species.     

Enhancement of growth of tilapia Oreochromis niloticus in iso-osmotic medium

Tilapia ( Oreochromis niloticus ) kept in 15 ppt sea water (roughly iso-osmotic salinity) had higher growth rates than fish kept in 0 ppt (freshwater) or 30 ppt seawater, but circulating level of growth hormone was highest in fish exhibiting the poorest growth rate (30 ppt seawater). Serum thyroxine concentration was highest in 15 ppt seawater. Intestinal trypsin may play a role in promoting growth in iso-osmotic salinity since its activity was highest in fish cultured in 15 ppt seawater. The results indicate that changes in the digestive power, coupled with changes in thyroxine secretion, may account for the variations in growth rate in tilapia reared under different salinities.     

Intraperitoneal Germ Cell Transplantation in the Nile Tilapia Oreochromis niloticus

Germ cell transplantation offers promising applications in finfish aquaculture and the preservation of endangered species. Here, we describe an intraperitoneal spermatogonia transplantation procedure in the Nile tilapia Oreochromis niloticus. Through histological analysis of early gonad development, we first determined the best suitable stage at which exogenous germ cells should be transplanted into the recipients. For the transplantation procedure, donor testes from a transgenic Nile tilapia strain carrying the medaka β-actin/enhanced green fluorescent protein (EGFP) gene were subjected to enzymatic dissociation. These testicular cells were then stained with PKH26 and microinjected into the peritoneal cavity of the recipient fish. To confirm colonization of the donor-derived germ cells, the recipient gonads were examined by fluorescent and confocal microscopy. PKH26-labeled cells exhibiting typical spermatogonial morphology were incorporated into the recipient gonads and were not rejected within 22 days posttransplantation. Long-term survival of transgenic donor-derived germ cells was then verified in the gonads of 5-month-old recipients and in the milt and vitelogenic oocytes of 1-year-old recipients, by means of PCR using EGFP-specific primers. EGFP-positive milt from adult male recipients was used to fertilize non-transgenic oocytes and produced transgenic offspring expressing the donor-derived phenotype. These results imply that long-term survival, proliferation, and differentiation of the donor-derived spermatogonia into vitelogenic oocytes and functional spermatozoa are all possible. Upon further improvements in the transplantation efficiency, this intraperitoneal transplantation system could become a valuable tool in the conservation of genetic resources for cichlid species.     

Overestimation of establishment success of non-native birds in Hawaii and Britain

The tens rules states that 10 % of all introduced species establish and about 10 % of those species become invasive. Several studies have failed to support the tens rule. However, these studies are beset by a general weakness: many unsuccessful invasions are never reported, and without these data tests of the tens rules are inadequate. Here, using data on the establishment success of non-native birds in Hawaii and Britain and comparing these data with those from a previous study, we show that lack of information about failed species introductions, and the tendency to report species that have become invasive more than those that have not, result in an overestimate of the establishment success and invasion rates of non-native species.     

An Important Natural Genetic Resource of Oreochromis niloticus (Linnaeus, 1758) Threatened by Aquaculture Activities in Loboi Drainage,Kenya

The need to improve food security in Africa through culture of tilapias has led to transfer of different species from their natural ranges causing negative impacts on wild fish genetic resources. Loboi swamp in Kenya is fed by three hot springs: Lake Bogoria Hotel, Chelaba and Turtle Springs, hosting natural populations of Oreochromis niloticus. The present study aimed at better genetic characterization of these threatened populations. Partial mtDNA sequences of the D-loop region and variations at 16 microsatellite loci were assessed in the three hot spring populations and compared with three other natural populations of O. niloticus in the region. Results obtained indicated that the hot spring populations had mitochondrial and nuclear genetic variability similar to or higher than the large closely related populations. This may be attributed to the perennial nature of the hot springs, which do not depend on rainfall but rather receive permanent water supply from deep aquifers. The study also revealed that gene flow between the three different hot spring populations was sufficiently low thus allowing their differentiation. This differentiation was unexpected considering the very close proximity of the springs to each other. It is possible that the swamp creates a barrier to free movement of fish from one spring to the other thereby diminishing gene flow. Finally, the most surprising and worrying results were that the three hot spring populations are introgressed by mtDNA genes of O. leucostictus, while microsatellite analysis suggested that some nuclear genes may also have crossed the species barrier. It is very likely that the recent intensification of aquaculture activities in the Loboi drainage may be responsible for these introgressions. Taking into account the importance of these new genetic resources, protection and management actions of the Loboi swamp should be accorded top priority to prevent the loss of these spring populations.     

Analysis of repetitive DNA sequences in the sex chromosomes of Oreochromis niloticus

In the Nile tilapia, Oreochromis niloticus, sex determination is primarily genetic, with XX females and XY males. While the X and Y chromosomes (the largest pair) cannot be distinguished in mitotic chromosome spreads, analysis of comparative hybridization of X and Y chromosome derived probes (produced, by microdissection and DOP-PCR, from XX and YY genotypes, respectively) to different genotypes (XX, XY and YY) has demonstrated that sequence differences exist between the sex chromosomes. Here we report the characterization of these probes, showing that a significant proportion of the amplified sequences represent various transposable elements. We further demonstrate that concentrations of a number of these individual elements are found on the sex chromosomes and that the distribution of two such elements differs between the X and Y chromosomes. These findings are discussed in relation to sex chromosome differentiation in O. niloticus and to the changes expected during the early stages of sex chromosome evolution.     

Mhc class I genes of the cichlid fish Oreochromis niloticus

In terms of number of species, perciform (perch-like) fishes are one of the most diversified groups of modern vertebrates. Within this group, the family Cichlidae is best known for its spectacular adaptive radiation in the great lakes of East Africa. The molecular tool kit used in the study of this radiation includes the major histocompatibility complex (Mhc) genes. To refine this tool, information about the organization of the Mhc regions is badly needed. In this study, the first step was taken toward providing such information for the Mhc class one regions of Oreochromis niloticus, a representative species of the tilapiine branch of the Cichlidae, for which good bacterial artificial chromosome library is available. Screening of the library with class I gene probes led to the identification and isolation of 31 class-I-positive clones. Sequencing of one of these clones and partial characterization of the remaining clones for the presence of class I exons resulted in the construction of two contigs representing the class I region of this species as well as identification of seven additional class-I-positive singleton clones. The O. niloticus genome was shown to contain at least 28 class I genes or gene fragments. The shorter of the two contigs was approximately 330 kb long and contained eight class I genes/gene fragments; the longer contig encompassed 1,200 kb of sequence and contained minimally 17 class I genes/gene fragments; three additional class I genes were found to be borne by a clone that might be part of the shorter contig. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. This work had been carried out in part at the Max-Planck-Institut für Biologie, Abteilung Immungenetik, Tübingen, Germany (A.S., R.D., N.T., S.S., and J.K.). The sequences reported in this paper have been deposited in the GenBank database (accession nos. AB270803–AB270897).     

Circadian Rhythms of Locomotor Activity in the Nile Tilapia Oreochromis niloticus

Behavioral rhythms of the Nile tilapia were investigated to better characterize its circadian system. To do so, the locomotor activity patterns of both male and female tilapia reared under a 12:12 h light-dark (LD) cycle were studied, as well as in males the existence of endogenous rhythmicity under free-running conditions (DD and 45 min LD pulses). When exposed to an LD cycle, the daily pattern of activity differed between individuals: some fish were diurnal, some nocturnal, and a few displayed an arrhythmic pattern. This variability would be typical of the plastic circadian system of fish. Moreover, reproductive events clearly affected the behavioral rhythms of female tilapia, a mouth-brooder teleost species. Under DD, 50% (6 of 12) of male fish showed circadian rhythms with an average period (τ) of 24.1±0.2 h, whereas under the 45 min LD pulses, 58% (7 of 12) of the fish exhibited free-running activity rhythms with an average τ of 23.9±0.5 h. However, interestingly in this case, activity was always confined to the dark phase. Furthermore, when the LD cycle was reversed, a third of the fish showed gradual resynchronization to the new phase, taking 7–10 days to be completely re-entrained. Taken together, these results suggest the existence of an endogenous circadian oscillator that controls the expression of locomotor activity rhythms in the Nile tilapia, although its anatomical localization remains unknown.