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1.
The genetic variations of rohu (Labeo rohita, Hamilton) sampled from five hatchery populations (Arabpur, Brahmaputra, Comilla, Kishorganj and Natore) and three major river populations (the Halda, the Jamuna and the Padma) were analysed by allozyme electrophoresis. Ten enzymes encoded by 11 loci were screened, and six were polymorphic. Alleles at three loci (Est‐1*, Gpi‐1* and Gpi‐2*) proved variable for hatchery and river populations, and the Mdh‐2* locus exhibited heterozygous genotypes for river populations only. Polymorphic loci per population (27.3±5.3%), heterozygous loci per individual (15.5±1.2%) and relative gene diversity (0.27±0.08) in river populations were higher than those for hatchery populations (25.5±1.8%, 10.7±1.6% and 0.25±0.01 respectively). Also, the observed heterozygosity (Ho) and expected heterozygosity (He) (0.09±0.03 and 0.14±0.04 respectively) in river populations were higher than those in hatchery populations (0.08±0.01 and 0.11±0.01 respectively). The lower levels of genetic variability in hatchery populations suggested the occurrence of inbreeding and/or genetic drift. The pairwise population differentiation (FST) values showed a lower level of genetic differentiation between hatchery and river population pairs. The unweighted pair‐group method with arithmetic mean dendrogram of Nei's genetic distances showed a relationship between the genetic distance and geographic distance. The populations were clustered into three groups: the Padma in one group, the Halda in second group and the Jamuna, including five hatcheries, in the third group. Highly diversified rohu individuals were observed in the Padma and Halda Rivers, whereas less genetically variable individuals were found in the Jamuna River and five hatcheries. These findings can be useful for rohu hatchery propagation to enhance the sustainable aquaculture production.  相似文献   

2.
This is the first controlled experiment to quantify the effect of introduced tilapia on indigenous species. This experiment was conducted in small earthen ponds (100 m2) to assess the impact of mixed‐sex or all‐male Nile tilapia (Oreochromis niloticus) on small indigenous species (SIS) commonly found in south Asia, mola (Amblypharyngodon mola), chela (Chela cachius) and punti (Puntius sophore). Ponds were fertilized, then stocked with 0.56 fish m?2 of water surface area in the mixed‐sex and all‐male tilapia treatments and 0.42 fish m?2 in the treatment without tilapia. No additional nutritional inputs were applied after stocking. Treatments were: mixed‐sex tilapia with SIS, mono‐sex male tilapia with SIS and SIS without tilapia (control). All treatments were stocked with 14 fish per species. All species reproduced during the 21‐month culture duration. The number of recruits varied by species, Tilapia reproduced in greater numbers than SIS. Tilapia numbers at harvest were the highest (451 ± 25/100 m2) in the mixed‐sex treatment compared with mola (221 ± 22/100 m2), chela (94 ± 8/100 m2) and punti (100 ± 7/100 m2). The number of mola was higher (399 ± 33/100 m2) in the all‐male tilapia treatment. There was reduction in the number of mola and chela in the treatment containing mixed‐sex tilapia. Gut content analysis combined with water sampling revealed that all fish species fed selectively. Significant interspecies dietary overlap was found between Nile tilapia and SIS and among SIS. Thus, there is potential for tilapia to compete with indigenous fish species when space and other resources are limiting, but a longer duration study with varying level of management is needed to determine how successfully tilapia competes with locally adapted SIS.  相似文献   

3.
A two‐factor experiment was performed to evaluate the effects of cage colour (black or white 0.5 m3 experiment cages) and light environment (natural sunlight or reduced level of natural sunlight) on the skin colour of darkened Australian snapper. Each treatment was replicated four times and each replicate cage was stocked with five snapper (mean weight=351 g). Snapper exposed to natural sunlight were held in experimental cages located in outdoor tanks. An approximately 70% reduction in natural sunlight (measured as PAR) was established by holding snapper in experimental cages that were housed inside a ‘shade‐house’ enclosure. The skin colour of anaesthetized fish was measured at stocking and after a 2‐, 7‐ and 14‐day exposure using a digital chroma‐meter (Minolta CR‐10) that quantified skin colour according to the L*a*b* colour space. At the conclusion of the experiment, fish were killed in salt water ice slurry and post‐mortem skin colour was quantified after 0.75, 6 and 22 h respectively. In addition to these trials, an ad hoc market appraisal of chilled snapper (mean weight=409 g) that had been held in either white or in black cages was conducted at two local fish markets. Irrespective of the sampling time, skin lightness (L*) was significantly affected by cage colour (P<0.05), with fish in white cages having much higher L* values (L*≈64) than fish held in black cages (L*≈49). However, the value of L* was not significantly affected by the light environment or the interaction between cage colour and the light environment. In general, the L* values of anaesthetized snapper were sustained post mortem, but there were linear reductions in the a* (red) and b* (yellow) skin colour values of chilled snapper over time. According to the commercial buyers interviewed, chilled snapper that had been reared for a short period of time in white cages could demand a premium of 10–50% above the prices paid for similar‐sized snapper reared in black cages. Our results demonstrate that short‐term use of white cages can reduce the dark skin colour of farmed snapper, potentially improving the profitability of snapper farming.  相似文献   

4.
This study was designed to determine the effect of complete substitution of fish meal (FM) by three plant protein sources including extruded soybean meal (SBM), extruded full‐fat soybean (FFSB) and corn gluten meal (CGM) on growth and feed utilization of Nile tilapia Oreochromis niloticus and tilapia galilae Sarothrodon galilaeus. Four isonitrogenous of crude protein (ca. 28.0%) and isocaloric (ca. 19 MJ kg−1) experimental diets were formulated. The control diet (diet 1) was prepared with FM as the main protein sources. Diets 2–4, each FM control diet, were completely substituted with SBM (diet 2), FFSB (diet 3) and CGM (diet 4). l ‐lysine and dl ‐methionine were added to plant protein diets to cover the nutritional requirements of tilapia. Each treatment was allocated to three net pens and fed for 17 weeks. Nile tilapia fed the control diet showed significantly higher (P≤0.05) values for final body weight (FBW), feed intake (FI), weight gain (WG) and specific growth rate (SGR), whereas fish fed the diet with CGM achieved the lowest values. Tilapia galilae fed SBM diet recorded the highest (P≤0.05) values for growth performance. Better feed conversion ratio (FCR) for both Oreochromis niloticus and Sarothrodon galilaeus was observed when fish were fed SBM diet, whereas the worse FCR was recorded for FFSB diet. Feed utilization parameters including protein productive value (PPV), fat retention (FR) and energy retention (ER) showed significant differences (P≤0.05) for both the species fed different dietary protein sources. The present results suggest that, for Nile tilapia, both SBM and FFSB supplemented with dl ‐methionine and l ‐lysine can completely replace dietary FM. Meanwhile, S. galilaeus fed SBM diet exhibited comparable growth and feed utilization with those fish fed a fish‐meal‐based diet.  相似文献   

5.
Genetic differentiation and variability data of two populations of two species of shrimp (Litopenaeus setiferus (L.) and L. schmitti (Burkenroad)) have been obtained by electrophoretic analysis and by analysis of 16S mitochondrial DNA. Using eight polymorphic enzymes, the genetic distance (GD) between the two species was 0.165. The GD between L. setiferus populations was 0.0057 and between L. schmitti populations it was 0.0034. The greatest differentiation was found within, rather than between, populations, although the differentiation value between Mexican and Cuban populations varied in accordance with the geographic distance and ecological characteristic of each. We found a high similarity between these two species with a bimodal distribution of the loci with respect to genetic identity. The homology percentages for gene 16S fragments were compared with those from six different shrimp species (L. vannamei, L. stylirostris, Farfantepenaeus notialis, Metapeneopsis lamellata) and Artemia salina. Ninety‐seven percent of identity was found by analysis of a 409 bp of 16S mitochondrial DNA. With these values a phylogenetic tree was made using parsimony criteria. The GDs obtained with this method confirm the classification proposed by Pérez‐Farfante & Kensley (1997) .  相似文献   

6.
Density and biomass estimates of pelagic fish are essential to understand food web interactions and ecosystem functioning. We conducted surveys of six subarctic lakes for assessing both mono‐ and polymorphic whitefish Coregonus lavaretus (L.) populations. Monomorphic whitefish lakes were inhabited by a habitat and diet generalist, large sparsely rakered (LSR) morph, whereas polymorphic whitefish lakes had a littoral benthivorous LSR morph, a pelagic planktivorous densely rakered (DR) morph and in two cases a benthivorous small sparsely rakered (SSR) morph inhabiting the profundal zone. In addition, an introduced specialist zooplanktivore, vendace Coregonus albula (L.), inhabited one of the monomorphic lakes. Hydroacoustics was found to be an appropriate method for estimating coregonid densities and biomasses in large and deep polymorphic lakes occupied by the planktivorous DR morph or vendace, but only during dark nights in autumn. The suitability of hydroacoustic assessment for benthivorous LSR and SSR morphs was low, especially in polymorphic whitefish lakes due to their preference for near‐bottom habitat or shallow areas not sampled with hydroacoustics. The pelagic density of DR morph varied from 330 to 1780 fish·ha?1 and biomass from 1.4 to 13.3 kg·ha?1 in polymorphic whitefish lakes, whereas corresponding estimates for LSR morph were 10–320 fish·ha?1 and 0.5–8.4 kg·ha?1 in monomorphic whitefish lakes. In general, polymorphism tended to increase the density and biomass of whitefish in the pelagic area compared with monomorphic systems.  相似文献   

7.
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.  相似文献   

8.
Streptococcus agalactiae infections in fish are predominantly caused by beta‐haemolytic strains of clonal complex (CC) 7, notably its namesake sequence type (ST) 7, or by non‐haemolytic strains of CC552, including the globally distributed ST260. In contrast, CC23, including its namesake ST23, has been associated with a wide homeothermic and poikilothermic host range, but never with fish. The aim of this study was to determine whether ST23 is virulent in fish and to identify genomic markers of fish adaptation of S. agalactiae. Intraperitoneal challenge of Nile tilapia, Oreochromis niloticus (Linnaeus), showed that ST260 is lethal at doses down to 102 cfu per fish, whereas ST23 does not cause disease at 107 cfu per fish. Comparison of the genome sequence of ST260 and ST23 with those of strains derived from fish, cattle and humans revealed the presence of genomic elements that are unique to subpopulations of S. agalactiae that have the ability to infect fish (CC7 and CC552). These loci occurred in clusters exhibiting typical signatures of mobile genetic elements. PCR‐based screening of a collection of isolates from multiple host species confirmed the association of selected genes with fish‐derived strains. Several fish‐associated genes encode proteins that potentially provide fitness in the aquatic environment.  相似文献   

9.
Hybridization among abalone species has been suggested as a possible means to increase their growth rates for aquaculture. As a first step to test the usefulness of the hybrids of Japanese abalone species (Haliotis discus discus, Haliotis gigantea and Haliotis madaka) for aquaculture, we characterized the genetic background and gonad development of hybrids that were produced by artificial insemination. The hybrid status of the resulting offspring was confirmed by assaying 14 allozymes and by RFLP analysis of the 16s rRNA and cytochrome oxidase I (COI) regions of mtDNA using 13 restriction enzymes. Histological examination of the gonads of the hybrids was conducted in comparison with those of the parental species. Cross‐breeding among the three species was conducted successfully in all combinations although with lower fertilization rates (means of 1.3–60.8%) than the parental species (34.3–90%). Crosses between H. discus discus and H. madaka had higher fertilization rates (22.4–60.8%) than those involving H. gigantea (1.3–19.9%). The hybrids were ascertained by the presence of both parental genotypes at the LDH‐A, ME‐A, MDH‐A and GPI loci. The maternal origin of the hybrid mtDNA was confirmed by digestion with DdeI, TaqI, HpaII of the COI region. No polymorphism was observed in the 16S rRNA region. The hybrids had gonadal development and maturity stages similar to the parental species up to fully mature oocytes and sperm. They spawned upon stimulation and produced viable offspring with high fertilization rates and successful development to the juvenile stage in back‐ and homologous hybrid crosses.  相似文献   

10.
This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90‐day trial based on 40 20‐m2 pens fixed in four 400‐m2 earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day?1 compared with 1.1–1.6 g per fish day?1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day?1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=?1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r2=0.98, P<0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha?1 day?1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day?1, P>0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day?1 and 1.6 g per fish day?1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha?1 day?1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P>0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha?1 day?1) was calculated at 4.06±0.08 g·m?2 day?1, which was significantly higher (P<0.001) than the yield (1.82±0.12 g·m?2 day?1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high.  相似文献   

11.
In an attempt to improve post‐harvest skin colour in cultured Australian snapper Pagrus auratus, a two‐factor experiment was carried out to investigate the effects of a short‐term change in cage colour before harvest, followed by immersion in K+‐enriched solutions of different concentrations. Snapper supplemented with 39 mg unesterified astaxanthin kg?1 for 50 days were transferred to black (for 1 day) or white cages (for 1 or 7 days) before euthanasia by immersing fish in seawater ice slurries supplemented with 0, 150, 300, 450 or 600 mmol L?1 K+ for 1 h. Each treatment was replicated with five snapper (mean weight=838 g) held individually within 0.2 m3 cages. L*, a* and b* skin colour values of all fish were measured after removal from K+ solutions at 0, 3, 6, 12, 24 and 48 h. After immersion in K+ solutions, fish were stored on ice. Both cage colour and K+ concentration significantly affected post‐harvest skin colour (P<0.05), and there was no interaction between these factors at any of the measurement times (P>0.05). Conditioning dark‐coloured snapper in white surroundings for 1 day was sufficient to significantly improve skin lightness (L*) after death. Although there was no difference between skin lightness values for fish held for either 1 or 7 days in white cages at measurement times up to 12 h, fish held in white cages for 7 days had significantly higher L* values (i.e. they were lighter) after 24 and 48 h of storage on ice than those held only in white cages for 1 day. K+ treatment also affected (improved) skin lightness post harvest although not until 24 and 48 h after removal of fish from solutions. Before this time, K+ treatment had no effect on skin lightness. Snapper killed by seawater ice slurry darkened (lower L*) markedly during the first 3 h of storage in contrast with all K+ treatments that prevented darkening. After 24 and 48 h of storage on ice, fish exposed to 450 and 600 mmol L?1 K+ were significantly lighter than fish from seawater ice slurries. In addition, skin redness (a*) and yellowness (b*) were strongly dependent on K+ concentration. The initial decline in response to K+ was overcome by a return of a* and b* values with time, most likely instigated by a redispersal of erythrosomes in skin erythrophores. Fish killed with 0 mmol L?1 K+ maintained the highest a* and b* values after death, but were associated with darker (lower L*) skin colouration. It is concluded that a combination of conditioning snapper in white surroundings for 1 day before harvest, followed by immersion in seawater ice slurries supplemented with 300–450 mmol L?1 K+ improves skin pigmentation after >24 h of storage on ice.  相似文献   

12.
Two experiments were conducted with Australian snapper Pagrus auratus (Bloch and Schneider, 1801). The first was aimed at determining the dietary level of astaxanthin that improved skin redness (CIE a*values) of farm‐reared snapper. Farmed snapper (ca. 600 g) fed a commercial diet without carotenoids were moved to indoor tanks and fed the same diet supplemented with 0, 36 or 72 mg astaxanthin kg?1 (unesterified form as Carophyll Pink?) for nine weeks. Skin redness (CIE a* values) continued to decrease over time in fish fed the diet without astaxanthin. Snapper fed the diet containing 72 mg astaxanthin kg?1 were significantly more red than fish fed the diet with 36 mg astaxanthin kg?1 three weeks after feeding, but skin redness was similar in both groups of fish after 6 and 9 weeks. The second experiment was designed to investigate the interactive effects of dietary astaxanthin source (unesterified form as Carophyll Pink? or esterified form as NatuRose?; 60 mg astaxanthin kg?1) and degree of shading (0%, 50% and 95% shading from incident radiation) on skin colour (CIE L*a*b*) and skin and fillet astaxanthin content of farmed snapper (ca. 800 g) held in 1 m3 floating cages. After 116 days, there were no significant interactions between dietary treatment and degree of shading for L*, a* or b* skin colour values or the concentration of astaxanthin in the skin. Negligible amounts of astaxanthin were recovered from fillet samples. The addition of shade covers significantly increased skin lightness (L*), possibly by reducing the effect of melanism in the skin, but there was no difference between the lightness of fish held under either 50% or 95% shade cover (P>0.05).  相似文献   

13.
A single‐factor experiment was conducted to investigate the effects of dietary astaxanthin concentration on the skin colour of snapper. Snapper (mean weight=129 g) were held in white cages and fed one of seven dietary levels of unesterified astaxanthin (0, 13, 26, 39, 52, 65 or 78 mg astaxanthin kg?1) for 63 days. Treatments comprised four replicate cages, each containing five fish. The skin colour of all fish was quantified using the CIE L*, a*, b* colour scale after 21, 42 and 63 days. In addition, total carotenoid concentrations of the skin of two fish cage?1 were determined after 63 days. Supplementing diets with astaxanthin strongly affected redness (a*) and yellowness (b*) values of the skin at all sampling times. After 21 days, the a* values increased linearly as the dietary astaxanthin concentration was increased before a plateau was attained between 39 and 78 mg kg?1. The b* values similarly increased above basal levels in all astaxanthin diets. By 42 days, a* and b* values increased in magnitude while a plateau remained between 39 and 78 mg kg?1. After 63 days, there were no further increases in measured colour values, suggesting that maximum pigmentation was imparted in the skin of snapper fed diets >39 mg kg?1 after 42 days. Similarly, there were no differences in total carotenoid concentrations of the skin of snapper fed diets >39 mg kg?1 after 63 days. The plateaus that occurred in a* and b* values, while still increasing in magnitude between 21 and 42 days, indicate that the rate of astaxanthin deposition in snapper is limited and astaxanthin in diets containing >39 mg astaxanthin kg?1 is not efficiently utilized. Astaxanthin retention after 63 days was greatest from the 13 mg kg?1 diet; however, skin pigmentation was not adequate. An astaxanthin concentration of 39 mg kg?1 provided the second greatest retention in the skin while obtaining maximum pigmentation. To efficiently maximize skin pigmentation, snapper growers should commence feeding diets containing a minimum of 39 mg unesterified astaxanthin kg?1 at least 42 days before sale.  相似文献   

14.
A 10‐week feeding trial of using housefly (Musca domestica) maggot meal (MM) in practical feeds for Nile tilapia (Oreochromis niloticus) was conducted to assess the growth performance, ingredient utilization, flesh quality, innate immunity and its influence on water environment. Fish were fed five isonitrogenous and isoenergetic diets, where fishmeal (FM) was substituted by MM at the level of 0, 90, 180, 270 and 360 g kg‐1 diet (remaining FM content: 360, 270, 180, 90 and 0 g kg‐1). There was no significant difference in feed intake and apparent digestibility coefficient between the treatments. Replacing up to 270 g kg‐1 FM did not have an impact on the growth performance and ingredient utilization, whereas the complete replacement of FM caused significantly lower survival rate, weight gain, specific growth rate and higher feed conversion rate. Dietary MM was also proved positively influential in flesh quality, whereas replacing 180 g kg‐1 or more FM suppressed the innate immunity of tilapia. When compared by the effects on the water environment, the increasing substitute levels were accompanied with the declining concentrations of nitrite nitrogen and total phosphorus in the water. Our study verified the feasibility of using MM as a partial substitute of FM in aquatic feed. When replacing 180 g kg‐1 FM (corresponding to half of the FM content in control diet) in the diet of Nile tilapia, it can serve as a renewable and environmentally superior alternative without compromising the performance criteria.  相似文献   

15.
A fast and cost‐effective protocol to develop candidate microsatellite markers from sea perch, Lateolabrax japonicus, was described here. Ten suites of codominant bands that contained seven microsatellites were discovered in this marine fish, in which no microsatellite development was reported previously. All the seven microsatellites were found to be polymorphic among tested 20 individuals of sea perch. Five of the above seven loci conformed to Hardy–Weinberg equilibrium (HWE) as determined by using the Markov‐Chain method implemented, the other two loci significantly deviated from HWE, both of them showed a large heterozygote excess (HE). Out of 21 possible pair‐wise comparisons among the seven loci applied to sea perch, none showed significant linkage disequilibrium (LD) (P > 0.008). Five additional fish species assessed for cross‐species amplification revealed that some of the loci appear to be applicable in close‐related species.  相似文献   

16.
Fertilization of ultraviolet (UV) irradiated oocytes of Nile tilapia, Oreochromis niloticus (L.), with sperm from O, niloticus or blue tilapia, O, aureus (Steindachner), and subsequent suppression of the first cleavage of fertilized eggs successfully induced androgenesis in Nile and blue tilapia. The optimal doses of UV irradiation to denucleate a female genome of Nile tilapia prior to androgenesis ranged from 5940 to 6930 erg mm?2 for 54-63 s at a fixed intensity of 110 erg mm?2 s?1. Putative androgenetic fish were created from eggs which were irradiated at various times and several durations of heat-shock. Eggs which were treated for 5 min at 41.6 oC at 2 7.5 min after fertilization were the most successful at suppressing the first cleavage and producing viable androgenetic diploids in Nile or hybrid Nile X blue tilapia. The maximal survivals of putative androgenetic diploids in relation to the control were 1.60% and 0.90% in Nile and hybrid Nile X blue tilapia, respectively. The androgenetic offspring established exhibited active feeding and normal growth.  相似文献   

17.
Diseases caused by motile aeromonads in freshwater fish have been generally assumed to be linked with mainly Aeromonas hydrophila while other species were probably overlooked. Here, we identified two isolates of non‐A. hydrophila recovered from Nile tilapia exhibiting disease and mortality after exposed to transport‐induced stress and subsequently confirmed their virulence in artificial infection. The bacterial isolates were identified as Aeromonas jandaei and Aeromonas veronii based on phenotypic features and homology of 16S rDNA. Experimental infection revealed that the high dose of A. jandaei (3.7 × 106 CFU fish?1) and A. veronii (8.9 × 106 CFU fish?1) killed 100% of experimental fish within 24 h, while a 10‐fold reduction dose killed 70% and 50% of fish, respectively. When the challenge dose was reduced 100‐fold, mortality of the fish exposed to A. jandaei and A. veronii decreased to 20% and 10%, respectively. The survivors from the latter dose administration were rechallenged with respective bacterial species. Lower mortality of rechallenged fish (0%–12.5%) compared to the control groups receiving a primary infection (37.5%) suggested that the survivors after primary infection were able to resist secondary infection. Fish exposed to either A. jandaei or A. veronii exhibited similar clinical signs and histological manifestation.  相似文献   

18.
Three 2‐factor experiments were conducted to determine the effects of background colour and synthetic carotenoids on the skin colour of Australian snapper Pagrus auratus. Initially, we evaluated the effects on skin colour of supplementing diets for 50 days with 60 mg kg?1 of either astaxanthin (LP; Lucantin® Pink), canthaxanthin (LR; Lucantin® Red), apocarotenoic acid ethyl ester (LY; Lucantin® Yellow), selected combinations of the above or no carotenoids and holding snapper (mean weight=88 g) in either white or black cages. In a second experiment, all snapper (mean weight=142 g) from Experiment 1 were transferred from black to white, or white to white cages to measure the short‐term effects of cage colour on skin L*, a* and b* colour values. Skin colour was measured after 7 and 14 days, and total carotenoid concentrations were determined after 14 days. Cage colour was the dominant factor affecting the skin lightness of snapper with fish from white cages much lighter than fish from black cages. Diets containing astaxanthin conferred greatest skin pigmentation and there were no differences in redness (a*) and yellowness (b*) values between snapper fed 30 or 60 mg astaxanthin kg?1. Snapper fed astaxanthin in white cages displayed greater skin yellowness than those in black cages. Transferring snapper from black to white cages increased skin lightness but was not as effective as growing snapper in white cages for the entire duration. Snapper fed astaxanthin diets and transferred from black to white cages were less yellow than those transferred from white to white cages despite the improvement in skin lightness (L*), and the total carotenoid concentration of the skin of fish fed astaxanthin diets was lower in white cages. Diets containing canthaxanthin led to a low level of deposition in the skin while apocarotenoic acid ethyl ester did not alter total skin carotenoid content or skin colour values in snapper. In a third experiment, we examined the effects of dietary astaxanthin (diets had 60 mg astaxanthin kg?1 or no added carotenoids) and cage colour (black, white, red or blue) on skin colour of snapper (mean weight=88 g) after 50 days. Snapper fed the astaxanthin diet were more yellow when held in red or white cages compared with fish held in black or blue cages despite similar feed intake and growth. The skin lightness (L* values) was correlated with cage L* values, with the lightest fish obtained from white cages. The results of this study suggest that snapper should be fed 30 mg astaxanthin kg?1 in white cages for 50 days to increase lightness and the red colouration prized in Australian markets.  相似文献   

19.
This study evaluated the effects of AQUI‐S®20E (10% eugenol) sedation on the survival and behaviour of yellow perch Perca flavescens (Mitchill) and Nile tilapia Oreochromis niloticus L. held in high loading densities. Fish were held in 0–300 mg L?1 AQUI‐S®20E (0–30 mg L?1 eugenol) for up to 10 h in static tanks. At 17°C, yellow perch held in 200 and 300 mg L?1 AQUI‐S®20E were lightly sedated for up to 7 h. Yellow perch at 200 and 300 mg L?1 AQUI‐S®20E also had >95% mean survival 7‐days post exposure using loading densities up to 360 g L?1. Nile tilapia were only sedated for ≤3 h in concentrations up to 300 mg L?1 at 22°C and had >90% mean survival at loading densities ≤480 g L?1. Ammonia in tanks increased significantly as loading density increased, but treatment with AQUI–S®20E did not reduce ammonia accumulation. Results suggest that AQUI–S®20E was effective to sedate yellow perch and Nile tilapia at high loading densities, but sedation varied with loading density and species.  相似文献   

20.
Fish polyculture is based on the assumption that each species has its own feeding niche and may increase the maximum standing crop of a pond by exploring a wider range of available food and ecological niches. In order to identify the better species ratio and to introduce jundia (JN) (Rhamdia quelen Quoy & Gaimard) and Nile tilapia (NT) (Oreochromis niloticus Linnaeus) in to the carp polyculture practiced in South Brazil, a 162‐day experiment was conducted, in 12 250‐m2 earthen ponds (1.2 m deep). Treatment I (T‐I) contained 35% common carp, Cyprinus carpio (L.) (CC); 35% grass carp, Ctenopharyngodon idella Valenciennes (GC); 15% silver carp, Hypophthalmichthys molitrix Valenciennes (SC); and 15% bighead carp, Aristichthys nobilis Richardson (BC). Treatment II (T‐II) consisted of three ponds stocked at the following ratio: 17.5% CC, 35% GC, 15% SC, 15% BC and 17.5% JN. Treatment III (T‐III) consisted of three ponds with 35% CC, 35% GC, 7.5% SC, 7.5% BC and 15% NT. Treatment IV (T‐IV) consisted of three ponds with 17.5% CC, 35% GC, 7.5% SC, 7.5% BC%, 17.5% JN and 15% NT. No significant correlation was found between the treatments with different species ratio and water quality parameters. The final weight of different species, in different treatments, was statistically different. The major result was the clear positive effect on growth parameters observed by the introduction of JN and/or NT in to the carp polyculture. The yield per hectare was 2083.33±183 kg ha?1 for polyculture with carp species; 2476.67±139.88 kg ha?1 following the introduction of JN only; 2801.67±111.42 kg ha?1 for isolated introduction of NT; and 2506.67±422.31 kg ha?1 for simultaneous introduction of JN and NT. The introduction of JN and/or NT had a positive effect on growth parameters when compared with carp‐only polyculture. The reduction in CC ratio also had a positive effect on growth parameters.  相似文献   

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