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.     

Large extent of mitochondrial DNA transfer from Oreochromis aureus to O. niloticus in West Africa

Introgressive hybridization has an important evolutionary significance in terms of gene diversity and speciation. Among the major groups of vertebrates, fish show a strong propensity to hybridize. In order to highlight the possible occurrence of gene flow between two tilapia species, Oreochromis niloticus and O. aureus, a comparison of allozyme and mitochondrial DNA (mtDNA) polymorphism was performed on sympatric and allopatric populations of these two species. Nuclear data were congruent with the morphological identification of O. niloticus and O. aureus populations. In opposition, the mtDNA analysis resulted in two strictly differentiated groups which did not follow the morphological and nuclear DNA classification. The first group consisted of East African O. niloticus populations and the second included all the O. aureus populations and the West African O. niloticus populations. Moreover, in some cases, the same sequences were detected in both species. These data strongly support a differential introgression of mtDNA from O. aureus to O. niloticus involving all the West African area. This work points out the risk of misinterpretation of mtDNA or nuclear DNA data when only one single class of marker is used.     

Breeding pattern of Oreochromis niloticus (Linnaeus, 1758) versus native congeneric species,Oreochromis macrochir (Boulinger, 1912), in the upper Kabompo River,northwest of Zambia

Investigating the determinants of the reproductive biology of fishes is an essential component of fisheries research. Tilapia breeding patterns were investigated to determine the impact of non‐native Oreochromis niloticus on the native congeneric Oreochromis macrochir in the upper Kabompo River in the Northwest of Zambia using the gonadosomatic index and the sex ratios. Oreochromis niloticus was the most abundant fish caught (221, 63.5%) than O. macrochir (127, 36.5%). Results showed that the overall gonadosomatic index means of O. macrochir in both sections were similar. Oreochromis macrochir bred in December and February–March, with no reproduction in June. However, O. niloticus in the invaded section indicated all year reproduction through reduced spawning in May–June, with increased spawning activity in February–March. The sex ratio (females: males) was 1:1.3 and 1:1.7 for O. niloticus and O. macrochir, respectively, and both significantly deviated from the sex ratio of 1:1 (ꭓ² = 8.42 and 9.37, p < .05). Our study has revealed that O. niloticus was able to spawn across all sampled months with a 23% higher breeding population than O. macrochir, which might explain the suppression in the abundance of native O. macrochir. Due to the superior breeding patterns of O. niloticus, fisheries, wildlife, and aquaculture practitioners need to make contingency plans to alleviate its impacts further downstream of the Kabompo River.     

The histology of mature gonads of Oreochromis (Nyasalapia) karongae (Trewavas)

Histology of gonads of Oreochromis karongae was undertaken to study internal cell characteristics during maturation. This study was necessitated by low spawning output of the fish species. Several oocyte stages, ranging from primary forms to vitellogenesis, suggest that the maturation was generally succesfully attained in the fish ponds. Pre‐vitellogenesis oocytes (oogonia to perinuclear stage) and more advanced vitellogenesis (primary vesicle to tertiary yolk vesicle) oocyte stages were all found in the same gonads. However, there were some discontinuities observed during stages 3 and 4, suggesting selective maturation. Failure of gonads to mature normally is attributed to an ecological crunch that was in a previous study associated with environmental factors. Atretic oocytes were also recorded in the same gonads, a sign that some oocytes failed to mature normally. This indicates insufficient stimuli for normal gonad development. Several stages of spermatogenesis (spermatocytes, spermatid and spermatozoa) were also found in the same gonads. Selective recrudescence was more pronounced in O. karongae because generally less oocytes attained final maturation stages compared to Oreochromis niloticus and other tilapias. This could be the main reason for low natural breeding that has been observed in both wild and captive stocks, and led to the abandonment of its use in aquaculture. This study corroborates findings of previous studies that depended solely on external gonad characteristics. Histology provides conclusive evidence from internal cell characteristics that other techniques are unable to show.     

Toxicological impact of Zinc Nano Particles on tilapia fish (Oreochromis mossambicus)

In this study we investigated the acute toxicity of Zinc Nano Particles (ZnO NPs) and bulk ZnO on tilapia fish (Oreochromis mossambicus). Oreochromis mossambicus was exposed to the different concentration of ZnO NPs, ZnO and mixed solution of both ZnO NPs and ZnO (20 ppb, 20 ppb, 20 ppb) respectively for 96 h. A very high impact was recorded in hematological parameters which shows significant increased (p < 0.05) in count of white WBCs and platelets in all the experimental groups compared tocontrol group. The count of RBCs, Hb, hematocrit and MCHC were significantly decreased. The remarkable changes which were recorded during this study were histopathological lesions in the gills of exposed fish including, disorganization of gill lamella, cartilaginous core disruption, lifting of epithelium, loss of secondary gill lamellae, blood congestion, fusion of secondary gills lamellae, shortening of secondary gills lamellae, atrophy and curling. Disassembly were seen in plasma membrane of liver along with blood congestion, pyknosis, necrosis, hyperplasia and formation of vacuoles. Intestinal alterations which were observed include shortening of villi, necrosis, detachment and fusion of villi and extreme goblet cells formation. It is concluded from the present study that high level of ZnO NPs, ZnO and mixed solution has a strong tendency to alter hematological parameters, histological architecture, therefore, the indiscriminate use of ZnO NPs and ZnO can subsidize in reducing the population of Oreochromis mossambicus in natural water bodies.     

Fine structure of chloride cells in freshwater- and seawater-adapted Oreochromis niloticus (Linnaeus) and Oreochromis mossambicus (Peters)

Ultrastructural features of branchial chloride cells in Oreochromis niloticus (Linnaeus) and O. mossambicus (Peters) adapted to both fresh water and sea water were compdred. In freshwater adapted fish of both species chloride cells showed similar morphological features. Multicellular complexes made of a mature chloride cell and one or more accessory cells sharing a single apical crypt have been observed. Whereas high percentages of 0. mossambicus survived at maximum salinity only a few individuals of 0. niloticus showed the capacity to adapt to sea water. In the seawater-adapted individuals of 0. niloficus and 0. rnossambicus the chloride cells showed a two- and three-fold increase in sizei. respectively. Most chloride cells are organized in large multi-cellular complcxcs with apical interdigitations of accessory cells and 'leaky junctions'. These results indicate that the difference in euryhalinity of the species studied is related to functional rather than structural differences.     

Reproductive aspects of Oreochromis niloticus (Perciformes: Cichlidae) at Coatetelco Lake, Morelos, Mexico

Sex ratio, size at maturity, maturity stages, fecundity and egg diameter of Oreochromis niloticus from Coatetelco Lake, Morelos State, Mexico, were studied from January to December 1993. Sex ratio (male:female) was approximately 1:1.02. Length at maturity was 117 mm (males) and 120 mm (females). The fecundity ranged between 104 and 709 eggs, with egg diameter from 1,000 to 3,000 microns. The gonadosomatic and hepatosomatic index indicate that the species breeds during summer and winter.     

Record of Blue tilapia Oreochromis aureus (Steindachner, 1864) in the Eerste River catchment,Western Cape province,South Africa

Oreochromis aureus was imported from Israel into South Africa in 1959 but data on its current status in South Africa are lacking. Genomic DNA was extracted and the COI gene amplified at the South African Institute for Aquatic Biodiversity. The identity of the sequences and specimens was determined using the Barcode of Life Data Systems and GenBank. Morphological and genetic assessment demonstrated that 11 specimens collected from two farm dams in the Eerste River System, Western Cape province, were Oreochromis aureus. A MaxEnt model compiled using global distribution, rainfall and temperature data predicted that large areas of southern Africa were climatically suitable for this species, indicating considerable invasion debt in southern Africa. As a result, surveys to assess for the extent of the invasion in South Africa and eradication of existing populations, if feasible, are recommended management actions.     

Palatability of Water Organisms for Nile Tilapia Oreochromis niloticus (Cichlidae)

Journal of Ichthyology - The palatability of six species of aquatic animals and five species of plants for the Nile tilapia Oreochromis niloticus was evaluated. Aqueous extracts of most organisms...     

Maturity and gonad changes of Oreochromis (Nyasalapia) karongae raised in fish ponds in Malawi

The reproductive biology of pond-raised Oreochromis (Nyasalapia) karongae was investigated. Gonad histology and gonadosomatic indices (GSIs) indicated a potential for multiple spawning in a season. Several peaks of oocyte-size distribution and several maturation stages occurred in the same gonad. GSIs of 2.5% and 1.4% were recorded in female and male fish, respectively. Three stages of oocyte maturation (primary growth, formation of yolk vesicles, vitellogenesis) and three stages of sperm development (spermatogonia, spermatid, spermatozoa) were observed. With the exception of the final maturation stage, all development phases seemed to proceed satisfactorily. The final stage of maturation was attained at oocyte size of 2.70 ± 0.54 mm and was selectively impaired in some female fish by a lack of deposition of vitellogenin. This abnormal condition led to atrophic oocytes lacking yolk granules and vesicles. Sexual maturation was attained at a relatively large size of 16.0 cm (114 g) compared with other tilapia of the mossambicoid group (i.e. Oreochromis mossambicus and Oreochromis shiranus ). A combination of gravimetric and histological techniques was successful in charting gonad changes and calibrating external against internal gonad features.     

Nonadditive expression of lipid metabolism pathway-related genes in intestine of hybrids of Nile tilapia females (Oreochromis niloticus) and blue tilapia males (Oreochromis aureus)

Nonadditive expression contributes to heterosis in hybrids. In this study, the expression profiles of twelve lipid metabolism pathway-related genes were investigated in the intestine of Nile tilapia (Oreochromis niloticus) ♀?×?blue tilapia (Oreochromis aureus) ♂ hybrid. The expression of genes from the hybrid were assigned to nonadditive and additive expression pattern groups and compared with expression patterns from Nile tilapia and blue tilapia. In the intestine of the hybrid, apoA4B was expressed at intermediate levels, but apoB and MTP were assigned to ELD-B and ELD-N categories, respectively. The LPL and LRP1 showed transgressive up-regulation in the hybrid, but LDLR was assigned to the ELD-B category. For fatty acid uptake related genes, only FABP11a was categorized as nonadditive expression with transgressive up-regulation, while CD36 and FABP3 were categorized as additive expression in the intestine of the hybrid. Two genes in triacylglycerol metabolism, namely, FAS and DGAT2, showed transgressive up-regulation in the hybrid. Most of the genes analyzed in the present study showed nonadditive expression (8 in 12), and five genes showed transgressive up-regulation. These results indicated that the stimulation of lipid metabolism in the hybrid compared to that of its parents. The hyperactive expression of these genes in the hybrid may be associated with the growth and lipid usage vigor.

     

Stress-induced water permeability changes in the tropical cichlid, Oreochromis niloticus (Trewavas)

The effect of short-term, experimentally-induced stress on the branchial water permeability of Oreochromis niloticus was studied. Both handling and thermal stress increased water permeability but apparently by different mechanisms. The enhancement of water permeability by acclimation temperatures and acute temperature changes had Q ₁₀ of 3.52 and 2.24 respectively. Environmental sodium concentration and acute hypoxia had no effect while hypercapnia and mild anaesthesia decreased water permeability. Both hypercapnia and mild anaesthesia probably elevated arterial pCO₂ with a concomitant reduction of metabolism.     

Validation of annulus formation in sagittal otoliths of three tropical cichlids Oreochromis andersonii (Castelnau, 1861), Oreochromis macrochir (Boulenger, 1912), and Coptodon rendalli (Boulenger, 1896)

The periodicity of growth zone formation in sagittal otoliths of Oreochromis andersonii, Oreochromis macrochir and Coptodon rendalli from the Upper Zambezi region, southern Africa, was validated to test the hypothesis that a single growth zone is deposited annually. Edge analysis was carried out on 754 O. andersonii (54–492 mm TL), 601 O. macrochir (83–438 mm TL) and 622 C. rendalli (45–379 mm TL) caught between August 2010 and August 2011 in Lake Liambezi and the Kavango, Kwando and Upper Zambezi rivers. This was corroborated for O. andersonii (n = 17) and C. rendalli (n = 16) using a fluorochrome marking experiment conducted in a large earthen pond (625 m², 1.5 m deep) adjacent to the Kavango River. Both methods demonstrated that growth zone deposition occurred annually in juvenile and adult fishes. For edge analysis, the highest proportion of otoliths with an opaque margin was observed in summer from October to December. The fluorochrome marking experiment, however, revealed that opaque zone deposition took place in winter between June and September when water temperatures were lowest (17°C), indicating a lag between opaque zone deposition and detection on the otolith edge.     

Further study of the embryonic development of Oreochromis niloticus (Cichlidae, Teleostei) using scanning electron microscopy

The chronology of development of Oreochromis niloticus embryos was examined by scanning electron microscopy (S.E.M.) and the external structures which evolved during the embryonic period were analysed. Twenty-four stages of embryonic development of this fish at 25°C are described with emphasis on the cleavage phases and morphogenesis of external organs and tissues. Because the development of internal organs could not be observed under S.E.M., the necessary investigation was completed by light microscopy.     

Morphological and functional body reconstruction in a teleost of the genus Oreochromis (Cichlidae)

The process of morphological and functional regeneration was followed on a tilapid fish, a cross of Oreochromis aureus × Oreochromis niloticus, by observations on movements and the use of X-rays. A four-year-old adult fish that lost its tail as post larva, including ten vertebrae, was able to reconstruct a novel and shorter central skeleton, including a specially modified urostyle. The enlarged and strengthened pterygiophores and their junctions with the dorsal and anal spine formed a fast-holding base for the fins, the posterior part of which largely performed the functions of the missing caudal fin. Although the fish was much shorter than usual, this male behaved and functioned normally. © 1994 Wiley-Liss, Inc.     

Initial development of Oreochromis niloticus (Teleostei: Cichlidae) otolith

Otoliths of Oreochromis niloricus initiate as separate protein granules, surrounded by numerous dark particles. These granules merge to form the sub-primordium, after a layer of calcium and a layer of protein has been added to each one. Large amounts of protein are accreted on to the subprimordium to form the primordium. Calcification takes place shortly afterwards. In the otocyst lumen filaments and vesicles are abundant and associated. They seem to contribute to the proteins of the primordium and the calcified otolith. Mitochondria, Golgi complexes and intracellular granules are abundant in the epithelium, from which vesicles extrude.     

Microsatellite marker based genetic linkage maps of Oreochromis aureus and O. niloticus (Cichlidae): extensive linkage group segment homologies revealed

Partial genetic linkage maps, based on microsatellite markers, were constructed for two tilapia species, Oreochromis aureus and Oreochromis niloticus using an interspecific backcross population. The linkage map for O. aureus comprised 28 markers on 10 linkage groups and covered 212.8 CM. Nine markers were mapped to four linkage groups on an O. niloticus female linkage map covering 40.6 CM. Results revealed a high degree of conservation of synteny between the linkage groups defined in O. aureus and the previously published genetic linkage map of O. niloticus.     

Kinematics of the pharyngeal jaws during feeding in Oreochromis niloticus (Pisces,Perciformes)

Cichlids possess a complex pharyngeal jaw apparatus, the osteological components of which are two upper pharyngeal jaws, articulating with the neurocranial base, and a single lower pharyngeal jaw. Quantitative cinera-diography revealed that pharyngeal food processing in Oreochromis niloticus involves transport, mastication, and swallowing, effected by cyclical pharyngeal jaw movements. Transport and swallowing occur by simultaneous retractions of both upper pharyngeal jaws. Food reduction (mastication) is effected by lower jaw elevation (compression) and protraction (shear) during upper jaw retraction. Each movement cycle contains a transport, reduction, and swallowing component, although their relative importance may vary within a feeding sequence. The upper and lower pharyngeal jaws show opposite anteroposterior movements during most of the cycle. Variations in the amplitudes and the durations of the different movement components reflect the consistency and the size of the food.