The use of fetal bovine serum for cryopreservation of stage III zebrafish (Danio rerio) ovarian follicles.

Although several studies on fish ovarian follicles cryopreservation have been carried out, their cryopreservation still remains unsuccessful. In this study, for the first time the effect of Fetal Bovine Serum (FBS) in combination with several concentrations of methanol (1, 2 or 4M) as cryoprotectant on stage III ovarian follicles viability was investigated and cryopreservation using controlled slow cooling was undertaken. Membrane integrity assessed by trypan blue (TB) staining and ATP level of stage III ovarian follicles were evaluated following cryoprotectant treatment and cryopreservation. The results showed that the survival of ovarian follicles after cryopreservation, assessed by TB staining, was significantly decreased using all three concentrations of CPAs solutions when compared to room temperature controls. The results showed a further decrease of viability when the TB test was performed 2h post-thaw. 2M methanol+10 percent FBS resulted in higher survival rate compared with the other methanol concentrations in combination with 10 percent FBS, viability results obtained 10 min and 2 hours post-thaw were 70.2 +/- 4.2 percent and 46.2 +/- 10.4 percent respectively. Whilst results obtained with 1M methanol supplemented with 10 percent FBS 10min and 2 hours post-thaw were 51.8 +/- 2.4 and 3.4 +/- 1.5 and those obtained with 4M supplemented with 10 percent FBS were 36.0 +/- 5.3 and 6.4 +/- P content was observed with all three cryoprotectant solutions indicating a compromised metabolic status. The addition of 10 percent fetal bovine serum to media used for cryopreservation zebrafish ovarian follicles did not allow the achievement of successful cryopreservation.

Studies on cryoprotectant toxicity to zebrafish (Danio rerio) ovarian tissue fragments.

Cryopreservation of ovarian tissue is a viable alternative to cryopreservation of oocytes and embryos in many species but it has not been studied in fish. Selection of cryoprotectant is an important step in designing cryopreservation protocols. In order to identify the optimum cryoprotectant (CPA) in a suitable concentration for zebrafish ovarian tissue cryopreservation, studies on toxicities of five commonly used cryoprotectants methanol, ethanol, dimethyl sulfoxide (DMSO), ethylene glycol (EG) and propylene glycol (PG) were carried out. Experiments were conducted on ovarian tissue fragments consisting of stage I and stage II ovarian follicles. Ovarian tissue fragments were incubated in 90% L-15 medium (pH 9) containing 1-4M cryoprotectants for 30min at 22°C. Three different tests were used to assess ovarian tissue fragment viability: trypan blue (TB) staining, fluorescein diacetate (FDA) combined with propidium iodide (PI) staining and adenosine 5´- triphosphate (ATP) assay. Results from these tests showed that ATP assay was more sensitive than FDA+PI or TB staining for assessing cryoprotectant toxicity to follicles in tissue fragments. Methanol and ethanol were the least toxic cryoprotectants tested. Cryoprotectant toxicity increased in the order of methanol/ethanol, DMSO, PG and EG. Ethanol was used for zebrafish ovarian tissue for the first time and the results showed that the effect of methanol and ethanol on ovarian tissue fragments were comparable. As methanol has been shown to be the most effective cryoprotectant for zebrafish ovarian follicles in our laboratory, the use of ethanol will also be considered in assisting future freezing protocol design. The present study also showed that stage II ovarian follicles are more sensitive to cryoprotectant treatment than stage I follicles in tissue fragments. The results obtained in this study provided useful information for ovarian tissue fragment cryopreservation protocol design in the future.

Cryopreservation of zebrafish (Danio rerio) oocytes by vitrification.

Cryopreservation of fish oocytes is challenging because these oocytes have low membrane permeability to water and cryoprotectant and are highly chilling sensitive. Vitrification is considered to be a promising approach for their cryopreservation as it involves rapid freezing and thawing of the oocytes and therefore minimising the chilling injury. In the present study, vitrification properties and the toxicity of a range of vitrification solutions containing different concentrations of Me2SO, methanol, propylene glycol and ethylene glycol were investigated. Two different base media and vitrification methods were compared. The effect of different post-thaw dilution solutions together with incubation periods on oocyte viability were also investigated. Stage III zebrafish oocytes were equilibrated in increasing concentrations of cryoprotectants for 30 min in 3 steps. Oocytes were thawed rapidly in a water bath and cryoprotectants were removed in 4 steps. Oocyte viability was assessed using trypan blue staining. The results showed that vitrification solutions V3 and V4 in KCl buffer had low toxicity and vitrified well. The survivals of oocytes after stepwise dilution using solutions containing permeable cryoprotectants were significant higher than those diluted in 0.5M glucose, and the use of CVA65 vitrification system improved oocyte survival when compared with plastic straws after 30 min at 22 degrees C post-thawing. Cryopreservation of zebrafish oocytes by vitrification is reported here for the first time, although oocyte survivals after cryopreservation assessed by trypan blue staining were relatively high shortly after thawing, they became swollen and translucent after incubation in KCl buffer. Further studies are needed to optimise the post-thaw culturing conditions.

Development of in vitro culture method for early stage zebrafish (Danio rerio) ovarian follicles for use in cryopreservation studies.

There have been no reported methods for in vitro growth of early stage ovarian follicles for fish and their cryopreservation is still under investigation. If cryopreservation of early stage ovarian follicles can be achieved, in vitro procedures for ovarian follicle culture, development, ovulation and fertilisation after cryopreservation would be needed. The aim of the present study was to develop an in vitro culture method for early stage zebrafish ovarian follicles for use after their cryopreservation. Procedures for in vitro culture of stage I (primary growth) and stage II (cortical alveolus) ovarian follicles were developed. The effects of concentration of L-15 medium, pH and the concentration of human chorionic gonadotropin (hCG) and activin A were studied. The results demonstrated that early stage zebrafish ovarian follicles can be cultured in vitro for 24 h, stage I and II ovarian follicles can grow to the sizes of early stage II and stage III ovarian follicles after hCG treatment. The method developed here is effective for assessing early stage zebrafish ovarian follicles growth competence in vitro. The results from the present study indicated that in vitro culture is the most reliable method for assessing ovarian follicle viability when compared with vital dye staining methods.

Effect of methanol and Me2SO exposure on mitochondrial activity and distribution in stage III ovarian follicles of zebrafish (Danio rerio).

In this study the effect of cryoprotectants that have been shown to be the least toxic to zebrafish ovarian follicles (methanol and Me(2)SO), on mitochondria of stage III ovarian follicles was evaluated. The mitochondrial distributional arrangement, mitochondrial membrane potential, mtDNA copy number, ATP levels and ADP/ATP ratios were assessed following exposure to cryoprotectants for 30 min at room temperature. Results obtained by confocal microscopy showed that 30 min exposure to 2M methanol induced a loss of membrane potential, although viability tests showed no decrease in survival even after 5h post-exposure incubation. Higher concentrations of methanol (3 and 4M) induced not only a decrease in mitochondrial membrane potential but also the loss of mitochondrial distributional arrangement, which suggested a compromised mitochondrial function. Furthermore 3 and 4M treatments resulted in a decrease in viability assessed by Fluorescein diacetate-Propidium iodide (FDA-PI) and in a decrease in mtDNA copy number and ADP/ATP ratio after 5h incubation following methanol exposure, indicating a delayed effect. The use of Me(2)SO, which is considered to be a more toxic CPA to zebrafish ovarian follicles than methanol, caused a decrease in viability and a sustained decrease in ATP levels accompanied by failure to maintain mtDNA copy number within 1h post-exposure incubation. These results indicated that even CPAs that are considered to have no toxicity as determined by Trypan blue (TB) and FDA-PI tests can have a deleterious effect on mitochondrial activity, potentially compromising oocyte growth and embryo development.

Cryopreservation of zebrafish (Danio rerio) blastomeres by controlled slow cooling.

Cryopreservation is now a common practice in the fields of aquaculture, conservation and biomedicine. One approach for maintaining the genetic diversity of both nuclear genome and mitochondrial DNA is cryopreservation of the blastomere. This study sets out to determine an optimum cryopreservation protocol for blastomeres isolated from 50% epiboly zebrafish embryos. Freezing was performed in 0.25 ml straws in a programmable freezer. The optimum slow cooling protocol is identified as 5 degree C per min, from 22 to -6 degree C, holding for 15 min, 0.3 degree C per min from -6 to -40 degree C, 2 degree C per min from -40 to -80 degree C, cells were held for 10 min at -80 degree C before plunging into the liquid nitrogen. Thawing was performed in a water bath at 28 degrees C for 15 s followed by four step-wise removal of the cryoprotectant. Blastomeres had the highest survival level (70.2 +/- 3.2%) when a mixture of 1.5 M dimethyl sulfoxide (DMSO) and 0.1 M sucrose were used as cryoprotectants. This was higher than that achieved with either of the sugar alternatives, trehalose (60.6 +/- 3.1%) or glucose (43.1 +/- 4.9%). In the present study, cryopreservation of 50 percent epiboly zebrafish blastomeres was studied for the first time using controlled slow cooling method.

Distributional arrangement of mitochondria in the granulosa cells surrounding stage III zebrafish (Danio rerio) oocytes.

Mitochondria play a vital role during oocyte maturation, fertilization, and embryo development. In this study, confocal microscopy with the mitochondrial membrane potential-sensitive dye JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide) was used to investigate mitochondria distribution and activity of stage III zebrafish ovarian follicles. To support the mitochondrial origin of the fluorescence obtained by JC-1, a second mitochondrial probe, MitoTracker Green FM, was used. Cryo-scanning and transmission electron microscopy were also used to validate the distribution and localization of mitochondria obtained by mitochondrial staining. The mitochondrial probes were unable to penetrate the oocyte, and as a result it was not possible to observe stained mitochondria in the oocyte cytoplasm. However, mitochondrial staining of the granulosa cell layer surrounding the stage III zebrafish oocyte exhibited a contiguous aggregation pattern of mitochondria. Cryo-scanning electron microscopy studies also showed the oocyte surface to be covered by polygonal patterns of ridges of the same dimensions as the distributional arrangement of mitochondria in the granulosa cells. Though the results suggested the need for defolliculation to assess mitochondrial distribution and activity in the stage III zebrafish oocyte cytoplasm, the findings of this study will contribute to our understanding of oogenesis and folliculogenesis processes in fish.

Effect of chilling and cryopreservation on expression of Pax genes in zebrafish (Danio rerio) embryos and blastomeres.

Cryopreservation is now common practice in the fields of aquaculture, conservation and biomedicine. However, there is a lack of information on the effect of chilling and cryopreservation at the molecular level. In the present study, we used real-time RT-PCR analysis to determine the effect of chilling and cryopreservation on expression of Pax2a, Pax2b, Pax5 and Pax8 which constitute one subgroup of the Pax gene family. As intact embryos of zebrafish have not yet been successfully cryopreserved, we have used two alternatives: chilling of intact embryos and cryopreservation of isolated blastomeres. Cryopreservation was found to affect the normal pattern of gene expression in zebrafish embryonic blastomeres. The trends, profile changes, in expression of Pax2a and Pax5 occurred to a lesser extent in frozen-thawed blastomeres than in fresh blastomeres whilst the opposite was true for Pax8. The trends in expression of Pax2b were delayed in frozen-thawed blastomeres compared to fresh blastomeres. Cryopreservation can therefore disrupt normal gene expression patterns in zebrafish embryonic blastomeres which could have a detrimental effect on embryo development.

Development of cryopreservation protocols for early stage zebrafish (Danio rerio) ovarian follicles using controlled slow cooling.

Cryopreservation of germplasm of aquatic species offers many benefits to the fields of aquaculture, conservation and biomedicine. Although successful fish sperm cryopreservation has been achieved with many species, there has been no report of successful cryopreservation of fish embryos and late stage oocytes which are large, chilling sensitive and have low membrane permeability. In the present study, cryopreservation of early stage zebrafish ovarian follicles was studied for the first time using controlled slow freezing. The effect of cryoprotectant, freezing medium, cooling rate, method for cryoprotectant removal, post-thaw incubation time and ovarian follicle developmental stage were investigated. Stages I and II ovarian follicles were frozen in 4M methanol and 3M DMSO in either L-15 medium or KCl buffer. Ovarian follicle viability was assessed using trypan blue, FDA+PI staining and ADP/ATP assay. The results showed that KCl buffer was more beneficial than L-15 medium, methanol was more effective than DMSO, optimum cooling rates were 2-4 degrees C/min, stepwise removal of cryoprotectant improved ovarian follicle viability significantly and stage I ovarian follicles were more sensitive to freezing. The results also showed that FDA+PI staining and ADP/ATP assay were more sensitive than TB staining. The highest follicle viabilities after post-thaw incubation for 2h obtained with FDA+PI staining were 50.7+/-4.0% although ADP/ATP ratios of the cryopreserved follicles were significantly increased indicating increased cell damage. Studies are currently being carried out on in vitro maturation of these cryopreserved ovarian follicles.

Studies on chilling sensitivity of early stage zebrafish (Danio rerio) ovarian follicles.

Cryopreservation of fish gametes is of great importance in aquaculture, conservation and human genomic research. The creation of gamete cryobanks allows the storage of genetic material of targeted species for almost unlimited time periods. Cryopreservation has been successfully applied to fish sperm of many species, but there has been no success with fish embryos and oocytes. One of the obstacles to fish oocyte cryopreservation is their high chilling sensitivity and especially at subzero temperatures. Although studies on late stage oocyte cryopreservation has been carried out, there have been no reported studies on cryopreservation of early stage ovarian follicles. The aim of this study is to investigate the chilling sensitivity of early stage zebrafish ovarian follicles before developing protocols for their cryopreservation. Experiments were conducted with stage I (primary growth), stage II (cortical alveolus) and stage III (vetillogenesis) ovarian follicles, which were chilled in KCl buffer and L-15 medium for up to 144h at -1 degrees C in a low temperature bath. Ovarian follicles were also exposed to 2M methanol or 2M DMSO in L-15 medium for up to 168h at -1 and -5 degrees C, respectively. Control follicles were kept at 28 degrees C. Ovarian follicle viability was assessed using trypan blue staining. The results showed that stage I and II ovarian follicles are less sensitive to chilling than stage III follicles. These results were also confirmed following in vitro maturation of the chilled ovarian follicles. The results also showed that L-15 medium is more beneficial than KCl buffer for ovarian follicles at all stages. The presence of both methanol and DMSO reduced chilling sensitivity of ovarian follicles at all stages with methanol being the most effective. The study indicated that stage I and II follicles are less sensitive to chilling than stage III follicles, and that early stage zebrafish ovarian follicles may be better candidates for cryopreservation.

Cryopreservation of zebrafish (Danio rerio) oocytes using improved controlled slow cooling protocols.

Cryopreservation of gametes provides a promising method to preserve fish genetic material. Previously we reported some preliminary results on cryopreservation of zebrafish (Danio rerio) oocytes using controlled slow cooling and determined the optimum cryoprotective medium and cooling rate for stage III zebrafish oocytes. In the present study, the effects of two different cryopreservation media, cryoprotectant removal method, final sample freezing temperature before LN(2) plunge, warming rate, and the post-thaw incubation time on oocyte viability were investigated. Commonly used cryoprotectant methanol and glucose were used in this study. Stage III zebrafish oocytes were frozen in standard culture medium 50% L-15 or in a sodium-free KCl buffer medium. Oocyte viability was assessed using trypan blue staining and ATP assay. The viability of oocytes frozen in KCl buffer was significantly higher than oocytes frozen in L-15 medium. The results also showed that fast thawing and stepwise removal of cryoprotectant improved oocyte survival significantly, with highest viability of 88.0+/-1.7% being obtained immediately after rapid thawing when assessed by trypan blue staining. However, after 2h incubation at 22 degrees C the viability of freeze-thawed oocytes decreased to 29.5+/-5.1%. Results also showed that the ATP level in oocytes decreased significantly immediately after thawing. All oocytes became translucent after freezing which complicated the use of GVBD test (in vitro maturation of oocytes followed by observation of germinal vesicle breakdown which results in oocytes becoming translucent). New oocyte viability assessment methods are urgently needed.

Cathepsin activities and membrane integrity of zebrafish (Danio rerio) oocytes after freezing to -196 degrees C using controlled slow cooling.

This study investigated enzymatic activity of cathepsins and the membrane integrity of zebrafish (Danio rerio) oocytes after freezing to -196 degrees C using controlled slow cooling. Stage III oocytes (>0.5mm), obtained through dissection of anaesthetised female fish and desegregation of ovarian cumulus, were exposed to 2M methanol or 2M DMSO (both prepared in Hank's medium) for 30min at 22 degrees C before being loaded into 0.5ml plastic straws and placed into a programmable cooler. After controlled slow freezing, samples were plunged into liquid nitrogen (LN) and held for at least 10min, and thawed by immersing straws into a 27 degrees C water bath for 10s. Thawed oocytes were washed twice in Hank's medium. Cathepsin activity and membrane integrity of oocytes were assessed both after cryoprotectant treatment at 22 degrees C and after freezing in LN. Cathepsin B and L colorimetric analyses were performed using substrates Z-Arg-ArgNNap and Z-Phe-Arg-4MbetaNA-HCl, respectively, and 2-naphthylamine and 4-methoxy-2-naphthylamine were used as standards. Cathepsin D activity was performed by analysing the level of hydrolytic action on haemoglobin. Oocytes membrane integrity was assessed using 0.2% Trypan blue staining for 5min. Analysis of cathepsin activities showed that whilst the activity of cathepsin B and D was not affected by 2M DMSO treatment, their activity was lowered when treated with 2M methanol. Following freezing to -196 degrees C, the activity of all cathepsins (B, D and L) was significantly decreased in both 2M DMSO and 2M methanol. Trypan blue staining showed that 63.0+/-11.3% and 72.7+/-5.2% oocytes membrane stayed intact after DMSO and methanol treatment for 30min at 22 degrees C, respectively, whilst 14.9+/-2.6% and 1.4+/-0.8% stayed intact after freezing in DMSO and methanol to -196 degrees C. The results indicate that cryoprotectant treatment and freezing modified the activities of lysosomal enzymes involved in oocyte maturation and yolk mobilisation.

Studies on cryoprotectant toxicity to early stage zebrafish (Danio rerio) ovarian follicles.

Cryoprotectants are substances characterised by their ability to reduce cryoinjury of biological materials during the course of freezing. Unfortunately cryoprotectants can be toxic for cells. The aim of this study is to investigate the toxicity of cryoprotectants to early stage ovarian follicles of zebrafish (Danion rerio) before designing protocols for their cryopreservation. Commonly used cryoprotectants methanol, dimethyl sulfoxide (DMSO), propylene glycol (PG) and ethylene glycol (EG) were studied. Experiments were conducted with stage I and II zebrafish ovarian follicles, which were incubated in 50% L-15 medium containing different concentrations of cryoprotectants (0.25-5M) for 30 min at room temperature. Stage III zebrafish ovarian follicles were also used as comparisons. Two different tests were used to assess ovarian follicle viability: trypan blue (TB) and Fluorescein diacetate (FDA) + propidium iodide (PI) staining. Both TB and FDA+PI tests indicated that cryoprotectant toxicity to ovarian follicles increased in the order of methanol, DMSO, PG and EG. FDA+PI test was shown to be more sensitive than TB staining. No Observed Effect Concentrations (NOECs) for stage I and II follicles were 2M, 1M, 0.5M, and 0.25M for methanol, dimethyl sulfoxide (DMSO), propylene glycol (PG) and ethylene glycol (EG) respectively when assessed with FDA+PI. Stage III ovarian follicles appeared to be more sensitive than stage I and II ovarian follicles.

Evaluation of zebrafish (Danio rerio) ovarian follicle viability by simultaneous staining with fluorescein diacetate and propidium iodide.

Reliable fish oocyte quality assessment methods are essential in developing protocols for cryopreservation as well as their in vitro maturation and fertilisation. Current ovarian follicle viability assessment methods either lack sensitivity (e.g. Trypan Blue staining-TB) or are stage dependent (e.g. in vitro maturation and observation of germinal vesicle breakdown-GVBD). The aim of the present study was to develop a new viability assessment method for zebrafish ovarian follicles that is reliable, sensitive and not-stage specific. Fluorescein Diacetate (FDA) and Propidium Iodide (PI) were used for the first time to assess viability of zebrafish ovarian follicles. After preliminary studies to evaluate the efficacy of FDA and PI, a combination of these two fluorochromes was subsequently chosen and compared with TB staining and GVBD test in a series of cryoprotectant toxicity studies and following cryopreservation using stage III ovarian follicles. In all cases the FDA-PI test proved to be more sensitive than TB staining but less sensitive than the GVBD test. Ovarian follicle survivals after 4M Methanol treatment for 30 min at 22 degree C were 67.4 +/- 4.4%, 43.9 +/- 3.8% and 19.6 +/- 1.9% using TB, FDA-PI and GVBD test respectively. Survivals after cryopreservation procedure were 38.9 +/- 4.0% and 28.9 +/- 2.5% using TB and FDA-PI respectively when Hank's solution was used as medium and 45.2 +/- 4.3% and 35.2 +/- 3.5% when KCl buffer was used. The results showed the method to be promising, and it may offer a new approach for viability assessment of fish ovarian follicles.

Development of a new method for isolating zebrafish oocytes (Danio rerio) from ovary tissue masses.

In order to study cryopreservation of zebrafish (Danio rerio) oocytes, large numbers of oocytes need to be isolated from the ovaries for experimental use. Zebrafish oocytes have been previously separated from ovaries mechanically and the method is laborious and time consuming. The aim of the present study was to develop a simple and rapid method for obtaining large number of morphologically and functionally intact zebrafish oocytes at different stages of development. Zebrafish ovaries were treated with three enzymes-trypsin, collagenase or hyaluronidase at different concentrations (0.2-1.6 mg/ml) for different time periods (5-20 min). Membrane integrity and development competence of the oocytes isolated mechanically and enzymatically from zebrafish ovary were assessed. The results showed that when optimal concentration and treatment time combinations were used, high separation and viability rates of oocytes could be obtained with all the three enzymes. The best conditions were confirmed as 1.6 mg/ml hyaluronidase treatment for 10 min or 0.4 mg/ml collagenase treatment for 10 min at 22 degrees C. Oocytes survivals after optimal hyaluronidase enzymatic separation were 96.6+/-0.7%, 92.9+/-1.3% and 94.6+/-0.9% for stages I, II and III oocytes, respectively using trypan blue staining. Successful enzymatic separation of zebrafish oocytes is reported here for the first time. The method developed in this study will undoubtedly assist investigations on cryopreservation of zebrafish oocytes and studies on zebrafish oocytes in general.

Development of a new rapid measurement technique for fish embryo membrane permeability studies using impedance spectroscopy.

Information on fish embryo membrane permeability is vital in their cryopreservation. Whilst conventional volumetric measurement based assessment methods have been widely used in fish embryo membrane permeability studies, they are lengthy and reduce the capacity for multi-embryo measurement during an experimental run. A new rapid 'real-time' measurement technique is required to determine membrane permeability during cryoprotectant treatment. In this study, zebrafish (Danio rerio) embryo membrane permeability to cryoprotectants was investigated using impedance spectroscopy. An embryo holding cell, capable of holding up to 10 zebrafish embryos was built incorporating the original system electrods for measuring the impedance spectra. The holding cell was tested with deionised water and a series of KCl solutions with known conductance values to confirm the performance of the modified system. Untreated intact embryos were then tested to optimise the loading capacity and sensitivity of the system. To study the impedance changes of zebrafish embryos during cryoprotectant exposure, three, six or nine embryos at 50% epiboly stage were loaded into the holding cell in egg water, which was then removed and replaced by 0.5, 1.0, 2.0 or 3M methanol or dimethyl sulfoxide (DMSO). The impedance changes of the loaded embryos in different cryoprotectant solutions were monitored over 30 min at 22 degrees C, immediately following embryo exposure to cryoprotectants, at the frequency range of 10-10(6)Hz. The impedance changes of the embryos in egg water were used as controls. Results from this study showed that the optimum embryo loading level was six embryos per cell for each experimental run. The optimum frequency was identified at 10(3.14) or 1,380 Hz which provided good sensitivity and reproducibility. Significant impedance changes were detected after embryos were exposed to different concentrations of cryoprotectants. The results agreed well with those obtained from conventional volumetric based studies.

Rapid ecotoxicological testing using transformed BF-2 cells incorporating a luminescent reporter gene.

Since there is an ethical need to minimise the experimental use of higher organisms such as fish, especially those used in acute toxicity testing, fish cells are considered to be useful surrogates for fish in toxicity screening. The use of fish cell lines in conventional bioassays such as neutral red retention assays is however labour intensive, lengthy and costly. The use of luminescent reporter genes has been explored in our laboratory. In this study, a transfected BF-2 cell line (BF-2/luc1) was used for rapid toxicity testing on selected chemicals and results were compared with those obtained with in vivo fish testing and in vitro fish cell neutral red retention assays. The effect of temperature on the sensitivity of BF-2/luc1 was also investigated. BF-2/luc1 cells were harvested and suspended in PBS at 2.5-3.0x10(6)cells/ml. Individual aliquots of the suspended cells (40 microl each) were incubated for either 0.5 or 6 h at room temperature (22 degrees C) in the presence or absence of the toxicants. Bioluminescence was assayed using 17.5 microl Brightglo luciferase reagent which lysed the cells and provided the substrate luciferin. Luminescence was measured in a luminometer (Turner TD 20/20). The EC50 values obtained from BF-2/luc1 cells (0.5-6 h) generally compared well with the LC50 values (24-96 h) obtained from the in vivo fish tests on a range of species. The present study also showed that BF-2/luc1 cell sensitivity increased significantly when incubation temperature during toxicant exposure increased from 15 to 35 degrees C. The use of luminescent reporter genes in monitoring fish cells offers the possible advantages of increased sensitivity over the neutral red retention assay and a more rapid test to replace stain based bioassays, and provides a rapid screening method that could reduce the need for acute fish toxicity testing.

Studies on cryoprotectant toxicity to zebrafish (Danio rerio) oocytes.

Cryopreservation of fish germ cells is an important measure in conservation of fish genetic material. Although investigations on cryopreservation of fish sperm and embryos have been carried out extensively, cryopreservation of fish oocytes has not been studied systematically. In the present study the toxicity of cryoprotectants to zebrafish (Danio rerio) oocytes was investigated. Commonly used cryoprotectants dimethyl sulfoxide (DMSO), methanol, ethylene glycol (EG), propylene glycol (PG), sucrose and glucose were studied. Stage III (vitellogenic), stage IV (maturation) and stage V (mature egg) zebrafish oocytes were incubated in Hank's medium containing different concentrations of cryoprotectants (0.25-4M) for 30 min at room temperature. Three different tests were used to assess oocyte viability: trypan blue (TB) staining, thiazolyl blue (MTT) staining and in vitro maturation followed by observation of germinal vesicle breakdown (GVBD). Results showed that the toxic effect of cryoprotectant on oocytes generally increased with increasing concentration. MTT test was shown to be the least sensitive testing method and gave poor correlation to subsequent GVBD results. Sensitivity of vital tests increases in the order of MTT, TB and GVBD. GVBD test showed that cryoprotectant toxicity to stage III zebrafish oocytes increased in the order of methanol, PG, DMSO, EG, glucose and sucrose. No Observed Effect Concentrations (NOECs) for stage III oocytes were 2M, 1M, 1M, 0.5M, less than 0.25M and less than 0.25M for methanol, PG, DMSO, EG, glucose and sucrose respectively. TB test also showed that the toxicity of tested cryoprotectants increased in the same order. The sensitivity of oocytes to cryoprotectants appeared to increase with development stage with stage V oocytes being the most sensitive.

Studies on the toxicity of dimethyl sulfoxide, ethylene glycol, methanol and glycerol to loach (Misgurnus fossilis) sperm and the effect on subsequent embryo development.

The process of sperm cryopreservation consists of several steps: equilibration of sperm in cryoprotectant medium, freezing of sperm to subzero temperatures, low temperature storage and thawing of the sperm suspension. It has been shown that cryopreservation can cause some damage to the genetic material of cells although the mechanism and significance of these changes are still unknown. The aim of this work was to study the effect of cryoprotectant equilibration process on genetic damage of Loach (Misgurnus fossilis) sperm, using embryo survival as an indicator. Decrease in embryo survival after the 20th stage is generally believed to result from the failure in the genome function of embryos. In the first set of the experiments, Loach sperm were equilibrated in cryoprotectants Me2SO, ethylene glycol, methanol and glycerol (0.6, 1.2, 2.5 M) for 60 min at 10 degree C. The effect of cryoprotectant equilibration on sperm was evaluated based on the survival of embryos derived from cryoprotectant treated sperm. Embryo survival was evaluated at the following stages: 7th, 14th, 17th, 20th, 23rd, 26th, 31st, 34th, 35th, 36th and 37th. Cryoprotectants at concentrations greater than 1.2 M had significant effect on the survival of the embryos after the 20th stage. The effect of glycerol was the most significant with 64.8 +/- 2.4% of embryos survival compared to 77.0 +/- 2.4% for control. Me2SO treatment also effects embryo survival significantly. Possible mechanisms of the genetic instability of cryoprotectants are discussed.

Combined physico-chemical and biological sensing in environmental monitoring.

Single-use conductivity and microbial sensors were used to investigate the effect of both species (chloride, nitrate, and sulphate) and concentration/osmolarity of anions on the metabolic activity of Escherichia coli. A new disposable, single-use conductivity sensor is described which is compatible with the CellSense mediated amperometric biosensor system. The effect of changing salinity and nitrate concentration on the response of E. coli to 3,5-dichlorophenol and mercuric chloride was determined. The implications for toxicity assessment of a hybrid sensing system, allowing the simultaneous monitoring of physico-chemical and biological data, are discussed.