Evaluation of some red tilapia strains for aquaculture: growth and colour segregation in hybrid progeny

Four red tilapia hybrids were evaluated for growth in earthen ponds and for colour distribution: ‘red’O. niloticus (L.) x O. niloticus (L.) or O. aureus (Steindachner). and O. niloticus or O. aureus x ‘white’ segregate of a Philippine red tilapia (Oreochromis sp.). The best growth was obtained in the ‘red’O. niloticus x O. niloticus and O. aureusx‘white’ hybrids, although they constituted only a little over 50% males. Of these two hybrids, the former is all-red, while the latter segregates into 35% red and 65% less attractive bronze-coloured individuals. Ways for establishing all-male populations of these two hybrids, for possible improvement of their performance, are discussed. Incompatibility between ‘red’O. niloticus females and O. aureus males, limiting fry production of this hybrid, was observed. The few fish of this hybrid obtained and tested proved to be all-male and all-red.     

Artificial Spawning of Tilapia Eggs1

A stripspawning methodology was evaluated for tilapia (oreochromid) species. This technique achieved an average hatching success of 68.6 ± 3.6% (N= 31). Female fecundity and spawning frequency were dependant on both genetical and husbandry factors. Egg yields for Oreochromis niloticus, O. mossambicus, and O. niloticus±O. mossambicus hybrids averaged 4.54, 10.86 and 10.36 eggs/g female/spawn, respectively. Female broodstock that were adapted to an intensive spawning regime exhibited a significant increase in fecundity. Additionally, egg survival was not affected by hydration for up to 15 minutes prior to fertilization. Results suggest that the strip spawning of tilapia species may be an efficient method of providing viable gametes for hatchery purposes.     

Electrophoretic evidence for extensive hybrid gene introgression into commercial Oreochromis niloticus (L.) stocks in the Philippines*

Abstract. The usefulness of isozyme and protein markers in identifying tilapia species and their hybrids is demonstrated Genetic characterization of Oreochromis niloticus populations from commercial farms, experimental stations, and government hatcheries in Luzon, Visayas and Mindanao in the Philippines indicates well-established introgression with O mossambicus Genetic differentiation of the O niloticus stocks, measured by Nei's genetic distance, was highly correlated with O mossambicus gene content The implications of these results for tilapia genetic improvement are discussed.     

An investigation of the possible causes for the loss of productivity in genetically improved farmed tilapia strain in Fiji: inbreeding versus wild stock introgression

Four microsatellite markers and a mitochondrial DNA (mtDNA) fragment were used to investigate two possible explanations for a reported decline in productivity of genetically improved farmed tilapia (GIFT) in Fiji: (i) a decline in genetic diversity (GD) and (ii) genetic introgression from feral tilapia populations. Genetic diversity was estimated using θ and allelic richness, while Bayesian clustering was used to assign individuals to genetic groups (K=2 or 3) to test for introgression. Differentiation among groups was estimated using F_ST analysis. Results indicate that genetic diversity had declined compared with a GIFT reference stock from WorldFish Centre, while there was little evidence for introgression from feral tilapia populations. Loss of genetic diversity most probably resulted from practices that have not actively managed genetic resources in the hatchery. While GIFT is considered to be an improved line of Nile tilapia (Oreochromis niloticus), mtDNA analysis here revealed haplotypes assigned previously to three discrete Oreochromis species (O. niloticus, Oreochromis mossambicus and Oreochromis aureus) in both the Fijian strain and the WorldFish Centre strain. Possible sources for the three divergent lineages are discussed. Results have implications for the management and future expansion of the tilapia culture industry in Fiji as well as in other Pacific island nations.     

Investigation into the mode of inheritance of allozyme and random amplified polymorphic DNA markers in tilapia Oreochromis mossambicus (Peters)

Feral Australian Oreochromis mossambicus (Peters) (Pisces: Cichlidae) and an interspecific hybrid population (most probably originally derived from crosses of O. mossambicus and O. niloticus stocks) were used as model organisms to study the inheritance patterns of 24 allozyme loci and 31 random amplified polymorphic DNA (RAPD) loci in tilapia. Single‐paired matings of parents of known genotype were used to generate families, and 10–15 full‐sib offspring from each mating were used to test for mode of inheritance. The majority of allozyme and RAPD loci tested segregated in a Mendelian fashion. Allozyme markers in general showed co‐dominant inheritance patterns, while RAPD markers conformed to expectations for band presence/absence under a dominant allele model. Although only a small number of families and offspring were used, the results highlight the suitability of allozymes and RAPDs as genetic markers for population analysis in tilapia.     

Comparative study of biochemical parameters in response to stress in Oreochromis aureus, O. mossambicus and two strains of O. niloticus

This study was aimed at detecting differences among tilapia species in immunological and biochemical parameters that are indicators for fish health. In addition, six blood parameters that are indicators of stress were measured, glucose concentration, ceruloplasmin activity, lysozyme activity, respiratory burst activity, haematocrit and leucocrit, and their levels were compared among groups. A calibration experiment was conducted with commercial stock of tilapia to optimize a protocol for measuring stress response in tilapia. An air exposure stress was induced to six groups of fish and blood samples were taken at six different times: 15 min, 1, 2.5, 4.5, 6 and 24 h, after inducing stress. The highest responses to stress were observed after 2.5–4.5 h. A second experiment was conducted with four tilapia species: Oreochromis aureus (Steindachner), O. mossambicus (Peters), a red strain and the wild type of O. niloticus L. Levels of serum biochemical components and parameters of the innate immunity response to stress were compared in ten fish from each species. Significant differences were observed. Oreochromis aureus differed from the other three species (notably from O. mossambicus) in most of the measured immune response traits (glucose concentration, lysozyme activity, haematocrit and levels of total protein and IgM after stress) and serum biochemical components (protein, albumin, triglyceride, cholesterol, calcium, magnesium, phosphorus, bilirubin and β‐hydroxybotiric acid). The identified differences suggest that hybrid families from O. aureus and O. mossambicus may be used to construct a segregating population for genetic analysis of the innate immune response to stress. Thus, these two species were bred for segregating F₂ population, suitable for quantitative trait loci studies for the innate immune response to stress.     

An evaluation of two types of containers for the artificial incubation of Oreochromis eggs

Abstract. Conical and round-bottomed incubating containers were evaluated for efficiency in producing Oreochromis fry. For Orcochromis niloticus (L.) and Oreochromis mossambicus (Peters): 0-, 12-, 24-, 48- and 72-h-old egg clutches were artificially incubated at 28°C in conical and round-bottomed containers. Hatching occurred within 72–84h and 90–102h after fertilization respectively compared to 96–120h for naturally incubated egg clutches. No significant differences (P > 0·05) were found between the hatch and survival rates of O. niloticus and O. mossambicus fry or between fry from the various ages of eggs. The type of containers, however, significantly (P < 0·05) influenced the hatchability and survival rates, the overall survival rate from fertilization being 60% and 85% for conical and round-bottomed containers respectively. Possible reasons for these differences are discussed. The feasibility of using the superior round-bottomed containers for artificial egg and fry incubation and the advantages for broodstock management to mass produce Oreochromis fry are discussed.     

Comparison of growth, fillet yield and proximate composition between Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia×Stirling red O. niloticus) males

A comparison was made of some productive traits of Stirling Nile tilapia (wild type) (Oreochromis niloticus, Linnaeus) and red hybrid tilapia (Florida red tilapia× Stirling red O. niloticus) males during a 98‐day grow‐out period. Twenty‐two males from each genetic group with initial weights of 139.0 g for O. niloticus and 207.3 g for the red hybrid were placed in triplicate tanks. The fish were fed with a feed containing 36.8% crude protein. Survival was 97.0% for the red hybrid and 83.3% for O. niloticus. Daily individual weight gains were 2.95 and 2.50 g and final body weights were 473.0 and 348.8 g for the red hybrid and O. niloticus respectively. Fillet yield was similar for both the species, with 33.4% for the red hybrid and 32.0% for O. niloticus. Fresh fillet lipid content was perceptibly less in the red hybrid (0.33%) than in O. niloticus (2.07%). Some benefits of a red low‐fat tilapia genotype are discussed.     

Dynamics of piscine francisellosis differs amongst tilapia species (Oreochromis spp.) in a controlled challenge with Francisella noatunensis subsp. orientalis

A 25‐week immersion challenge was conducted exposing Oreochromis mossambicus, Oreochromis aureus and Oreochromis urolepis hornorum to Francisella noatunensis subsp. orientalis (Fno). Two populations were compared for each fish species; ‘resident fish’ were defined as fish maintained in tanks since week 0 of challenge, whereas ‘naïve fish’ were defined as fish added to tanks once temperature in water reached <26 °C at 21 weeks post‐challenge. Fno genome equivalents (GEs) in water were similar in all treatments 1 h post‐challenge; however, significantly lower Fno GEs were detected 2 weeks post‐challenge in all tanks, and the only treatment with detectable Fno GE after 4 weeks of challenge were the O. mossambicus tanks. Twenty‐one weeks post‐challenge, naïve fish were stocked with ‘resident’ cohorts. Over a 4‐week period, mortalities occurred consistently only in O. mossambicus naïve cohorts. Overall presence of granulomas in spleen of survivors was similar (>55%) in all resident populations; however, in naïve populations, only O. mossambicus presented granulomas. Similarly, only O. mossambicus presented viable Fno in the spleen of survivors, and Fno GEs were only detected in O. mossambicus, and in resident O. aureus. In conclusion, the results of this study suggest different susceptibility of tilapia species to piscine francisellosis.     

The influence of stocking density and food ration on fry survival and growth in Oreochromis mossambicus and O. niloticus female × O. aureus male hybrids reared in a closed circulated system

First-feeding stage tilapia fry were reared for 40 or 50 days in 20-l capacity aquaria at six stocking densities (2, 4, 6, 8, 10, 12 l^?1) and three feeding levels (6, 12, 24% of body weight daily). Fry survival and growth were improved at the higher feeding levels, but the percentage of fry surviving showed no consistent relationship to stocking density. Cannibalism accounted for a mortality rate of 10–35% in each experimental group and was inversely related to the level of feeding. Under equivalent conditions, O. niloticus female × O. aureus male fry had a higher rate of survival, better food conversion and were more uniform in size than O. mossambicus fry.     

Studies on fish heterosis with DNA fingerprinting

One Tilapia hybridization, Oreochromis aureus, (Steindachner) ♂ × Oreochromis niloticus, (Linnaeus) ♀, and two common carp, Cyprinus carpio, (Linnaeus) ♂, hybridizations, Russian mirror carp ♂ × Xingguo red carp ♀, and German mirror carp ♂ × Xingguo red carp ♀ were used to study the feasibility of predicting heterosis using genetic distance from DNA fingerprinting. The results indicated that highly polymorphic DNA fingerprints could be obtained with human minisatellite 33.6 as a probe on the studied varieties. The within‐population similarity indices of O. aureus, O. niloticus, Russian mirror carp, German mirror carp and Xingguo red carp were 0.785, 0.577, 0.432, 0.348 and 0.339 respectively. The similarity indices between F1 and their parents of three hybridization combinations were not significantly different (P > 0.05). There were larger genetic distances between two hybridization combinations, O. aureus♂ × O. niloticus♀ and Russian mirror carp ♂ × Xingguo red carp ♀, which showed heterosis in production and were extensively used in Chinese aquaculture. The genetic distance between O. aureus♂ and O. niloticus♀ was 0.338, and that between Russian mirror carp and Xingguo red carp was 0.344. However, the genetic distance between German mirror carp and Xingguo red carp was 0.129; this corresponded with the fact that their F1 generation did not show heterosis in the Chinese fish hybridization experiment. The study suggested that genetic distance could be used to predict fish heterosis.     

Cold tolerance of tilapia species and hybrids

Several experiments were conducted,involving Oreochromis mossambicus, O. aureusand their F₁ and F₂ hybrids to studythe genetic basis of cold tolerance in tilapiinefishes. Groups of fish, of similar age and grown underidentical conditions, were housed in replicated netenclosures in a controlled cooling water system.Survival time through a regime of controlledtemperature reduction was the observed parameter forcold tolerance. Intra-population variation anddifferences among species, hybrids and repeated spawnswithin a species were examined. There was nocorrelation between cold tolerance and fish size(within the range of 23–105mm standard length), andthe distribution for the trait was not normal. O. mossambicuswas the most cold-sensitive group,followed by the F₂, and the F₁ which wassimilar to O. aureus. Genetic variation in coldtolerance seems to have a large dominance component,based on the similarity of the F₁ hybrid to the O. aureus parent.     

A genome scan of a four-way tilapia cross supports the existence of a quantitative trait locus for cold tolerance on linkage group 23

A genome scan, searching for quantitative trait loci (QTL) for the traits cold tolerance and body weight in tilapia, was performed on a cross between a (Oreochromis niloticus×Sarotherodon galilaeus) male and a (O. mossambicus×O. aureus) female. Fifty‐four microsatellites and 23 amplified fragment length polymorphism (AFLP) primer combinations were genotyped and tested for marker–trait associations. Sex‐specific linkage maps were constructed from this data. Twenty‐three point‐wise significant marker–trait associations were found in the genome scan, and putative QTL were subsequently tested in another (On×Sg) × (Om×Oa) family. None of the putative QTL from the first experiment were significant in the second experiment. However, one microsatellite, UNH130, found to be associated to weight in the first experiment, was found to be strongly associated to cold tolerance in the second experiment. Since QTL for cold tolerance and body weight were recently found on the linkage group containing UNH130 (linkage group 23) in another study, this linkage group was investigated more closely using interval mapping. The results provide indications, but not conclusive evidence, of a QTL for cold tolerance on linkage group 23.     

Impact of Oreochromis mossambicus × O. niloticus (Pisces: Cichlidae) hybridization on population reproductive potential and long-term influence on a reservoir fishery

Abstract Exotic cichlids, introduced to Asia during the second half of the twentieth century, contribute significantly to the reservoir fisheries in the region. The two major cichlid species, Oreochromis mossambicus (Peters) and O. niloticus (L.), tend to interbreed easily. In Sri Lankan reservoirs, introgressive hybridization of these two cichlids takes place. The reproductive biology of O. mossambicus, O. niloticus and their hybrids in three reservoirs in Sri Lanka was evaluated. An imbalance in sex ratio with male dominance was evident. The estimated fecundity for 20-cm fish, using fecundity-total length relationships for various populations, indicated that there was a decline in fecundity in hybrid forms. It is hypothesized that the long-term effect of crosshybridization between the two cichlids might lead to a decline in fish yields in perennial reservoirs of Sri Lanka. The importance of the findings of the present study for the management of the reservoir fisheries in Asia is highlighted.     

A qualitative ecological risk assessment of the invasive Nile tilapia,Oreochromis niloticus in a sub‐tropical African river system (Limpopo River,South Africa)

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Genetic improvement of farmed tilapias: Biochemical characterization of strain differences in Nile tilapia

Four African wild strains (Egypt, Ghana, Senegal and Kenya) and four established Asian farmed strains of Nile tilapia, Oreochromis niloticus (popularly known in the Philippines as Taiwan, Thailand, Singapore and Israel) were analysed electrophoretically at 30 protein loci to estimate genetic differences among the strains. All strains shared alleles at 14 monomorphic and 16 variable loci. Among the African strains, characteristic allele frequency differences were observed at AAT-1 ^* 46 for Ghana and Senegal, ADH ^* 83 for Kenya, ADH ^* 120 for Senegal, G3PDH-2 ^* 300 for Egypt, IDDH ^* 67 for Senegal, sMDH-1 ^* 120 for Kenya and SOD ^* 150 for Senegal. Genetic distance values among the strains revealed a clustering of the farmed strains with Egypt and Ghana O. niloticus, a slight separation of the Senegal strain and a larger separation of the Kenya strain. This profile may reflect the origins of the few founder populations of this species previously introduced to Asia. It also confirms the wider genetic divergence of the Kenya strain (O. niloticus vulcani) from the others studied here, which are all O. n. niloticus. Observed heterozygosities of the strains ranged from 0.026 to 0.071, with the African wild strains the lower values (mean Ho = 0.036) and the farmed strains the higher ones (mean Ho = 0.056). The implications of these results to the ongoing tilapia genetic improvement programme in the Philippines are discussed.     

A growth comparison among three commercial tilapia species in a biofloc system

Despite a worldwide boom in tilapia aquaculture, South Africa has failed to follow suit, resulting in a small, very much undeveloped local industry. Much of the justification for this reality lies on the inadequacy of the species used and the stringent legislation preventing the use of the Nile tilapia, Oreochromis niloticus. With momentum gained in recent years, the local industry lobbying for the legalization of the O. niloticus has made great progress and its use in certain systems has recently been facilitated. This study was conducted to compare the growth performance between the indigenous Mozambique tilapia, Oreochromis mossambicus, another African alternative gaining momentum in Zambia, the Three Spot tilapia, Oreochromis andersonii, and the globally reputable O. niloticus. The study was conducted in a biofloc technology (BFT) system, showing great potential as an environmentally friendly technology. The trial was run for 10 weeks with 60 fish/tank stocked into four repeats tanks per species. Fish were sampled on six occasions with a regression fitted to the mass data. Oreochromis niloticus showed a significantly higher growth rate with an average daily gain of 0.693 ± 0.018 g/day and the lowest feed conversion ratio (FCR) of 1.01 ± 0.05, followed by O. mossambicus with average daily gain of 0.405 ± 0.025 g/day and FCR of 2.24 ± 0.16, and then O. andersonii with an average daily gain of 0.185 ± 0.025 g/day and an FCR of 2.53 ± 0.28, respectively. From this study, O. niloticus therefore appears to be the most adequate species for use in BFT systems in South Africa.     

Pink body colour in Tilapia shows single gene inheritance

Segregation of a wide range of body colour in the progenies was observed in breeding experiments with the Taiwanese red tilapias. Homozygous stocks of pink, red and golden colour morph were selected from such a stock by brother-sister crossing for six generations. DNA fingerprinting analysis using multilocus M13 and Bkm 2(8) probe and HinfIenzyme combinations of pink individuals, showed homozygosity in their genome. Pink individuals when crossed to black Oreochromis mossambicus (Peters) resulted in all pink F1 progenies. F1 X F1 crosses resulted in segregation of pink and black in the F2 progenies in a 3 : 1 ratio. F1 pink individuals when backcrossed to O. mossambicus gave progeny in the ratio of 1: 1 of pink and black. Black individuals from the F2 generation, when crossed to O. mossambicus and pink separately, resulted in all black and all pink progenies, respectively. These results show that the pink colour is dominant over the black phenotype and is inherited as an autosomal locus with complete penetrance.     

The expression of selected genes linked to metabolic homeostasis in obese pansteatitis‐suffering Mozambique tilapia,Oreochromis mossambicus (Peters)

The Oreochromis mossambicus (Peters) population inhabiting Lake Loskop, South Africa, is characterized by a high incidence of obesity and pansteatitis. We investigated potential links between the impaired health of Lake Loskop O. mossambicus and the endocrine system by assessing the expression of selected genes associated with the thyroid and adrenal endocrine axes as well as peroxisome proliferator‐activated receptor gamma (pparg). Moreover, contaminant‐induced thyroid and/or metabolic modulation in Lake Loskop water was evaluated using juvenile O. mossambicus in laboratory exposures. The expression of thyroid hormone receptor alpha (thra) and type 2 deiodinase (dio2) was higher in Lake Loskop O. mossambicus than fish from another population, suggesting a degree of thyroid disruption. The altered gene expression may be a consequence, rather than cause of obesity. Expression of dio2 and pparg was higher in juvenile O. mossambicus exposed to unfiltered compared to filtered lake water, and our data suggest fasting as causative factor. Micro‐organism abundance can therefore be a confounding factor in studies applying molecular markers to test for thyroid modulation by environmental waters. Pansteatitis was not a significant source of variance in the expression of any of the genes investigated, suggesting that the disease is not associated with disrupted endocrine signalling.