Flow cytometric characterization of hemocytes of the flat oyster, Ostrea chilensis.

The flat oyster, Ostrea chilensis, native to New Zealand (NZ) and Chile is considered an important ecological, cultural and fisheries resource. Currently, commercial landings of this species in NZ are restricted due to low population numbers caused by ongoing mortalities resulting from the presence of the haplosporidian parasite, Bonamia exitiosa. More recently, the arrival of B. ostreae in NZ led to major mortalities in farmed stocks. To understand how diseases caused by Bonamia spp. affect this oyster species, a more complete understanding of its biology, physiology and immune system is needed. The present study characterized, for the first time, hemocytes of adult O. chilensis, from the Foveaux Strait, NZ, using flow cytometry (FCM) and histology. Based on the internal complexity of the hemocytes, two main circulating hemocyte populations were identified: granulocytes and hyalinocytes (accounting for ~30% and ~70% of the total circulating hemocyte population, respectively). These were further divided into two sub-populations of each cell type using FCM. A third sub-population of granulocytes was identified using histology. Using FCM, functional and metabolic characteristics were investigated for the two main hemocyte types. Granulocytes showed higher phagocytic capabilities, lysosomal content, neutral lipid content and reactive oxygen species production compared to hyalinocytes, indicating their important role in cellular immune defence in this species. Methods of hemocyte sampling and storage were also investigated and flow cytometric protocols were detailed and verified to allow effective future investigations into the health status of this important species.

Development of a method to cryopreserve Greenshell mussel™ (Perna canaliculus) veliger larvae.

Cryopreservation of larvae of Greenshell™ mussel Perna canaliculus, the most cultivated species in New Zealand, can provide flexibility for selective breeding programmes and enhance its global production. In this study, we set out to develop a reliable protocol for freezing D-stage larvae of Greenshell™ mussels that ensured long-term survival for successful rearing of thawed larvae in the hatchery. The effects of different combinations of cryoprotecting agents (CPA), varying CPA equilibration times, larval concentrations per straw as well as different larval development stages (48 h vs 72 h old) were evaluated by assessing the behavioural response (swimming activity, algal consumption), shell size and survival of larvae, up to 4 days post-thawing. The protocol yielding the best larval performances was a combination of the following CPA (final concentrations): 14% ethylene-glycol (EG) + 0.6 M trehalose (TRE) + 1% polyvinyl-pyrrolidone (PVP), prepared with Milli-Q water. Stocking densities ranging from 50,000 to 150,000 larvae per straw (0.25 mL) and a 20 min equilibration time gave the best results, while no significant differences in fitness were found between larvae cryopreserved at 48 h nor 72 h-old. Using the improved cryopreservation protocol, over 50% of previously cryopreserved D-larvae were able to survive after 4 days of rearing, compared with 65% in the unfrozen control. More importantly, about one third of thawed larvae were able to swim and feed, and to potentially develop further. These findings contribute to enhance the selective breeding programmes for this species.

Development stage of cryopreserved mussel (Perna canaliculus) larvae influences post-thaw impact on shell formation, organogenesis, neurogenesis, feeding ability and survival.

Cryopreservation of genetic material from farmed aquatic species is a valuable technique to advance selective breeding programs for stock improvement. In this study, effects of cryopreservation on development of trochophore and D-stage larvae of Greenshell™ mussel (Perna canaliculus) were evaluated through histology, light microscopy, scanning electron microscopy, and confocal microscopy. Larvae of both life stages were motile immediately post-thawing, but survival declined rapidly from 4 days post-fertilisation (dpf). At 18 dpf, ~23% of non-cryopreserved control larvae had progressed to the pediveliger stage, while <1% of cryopreserved larvae had survived. Control larvae grew faster and larger, and consumed more food than larvae cryopreserved at either life stage (trochophore or D-stage). Settlement competency was achieved in the control larvae at 21 days post-fertilization, with most remaining individuals developing eye spots. Organogenesis was delayed in all cryopreserved larvae, and eyespots did not appear at all. Neurogenesis was stunted in cryopreserved trochophore larvae but seemed to progress almost normally in their cryopreserved D-stage counterparts. Developing abnormalities in shell morphology rapidly became apparent in all mussels post-thaw, with trochophore larvae being most highly afflicted. These delays in organogenesis and overall development are indicative of cryo-injuries sustained at a cellular level. Our results show that D-stage larvae are somewhat more resilient to cryopreservation than trochophore larvae. D-larvae are good life-stage candidates for cryobanking genetic resources in this species because there is generally an excess of larvae from selective breeding family crosses and these can be banked and stored for later use. Further on-going research aims to improve the long-term viability of cryopreserved D-larvae for successful rearing.

Cryopreservation: Extending the viability of biological material from sea urchin (Echinometra lucunter) in ecotoxicity tests.

The sea urchin, Echinometra lucunter, is widely used in embryo-larval tests for ecotoxicological studies in Brazil and other countries. For each test, sea urchins are collected from the wild and this can cause impact on wild populations and it is limited by the weather and season which in turn limits the ability to carry out the tests. Cryopreservation is a method of live biological material storage at low temperature and can be used for long periods with little decline in viability, reducing the number of animals taken from the wild and enabling testing to be carried out on demand, irrespective of spawning season or location. In this study, 15 combinations of cryoprotective agents (CPAs) were evaluated on spermatozoa, subjected to a rapid cooling curve followed by immersion in liquid nitrogen. Twenty-four CPA combinations were evaluated on eggs subjected to a more gradual cooling curve in nitrogen vapor down to -35 °C and then plunging in liquid nitrogen. Fertilization tests using cryopreserved spermatozoa gave high pluteus larvae yields (≈80%) when concentrations of 10.5% or 13.65% ME2SO or 13.65% ME2SO+15.75% sucrose were used. The higher concentrations of ME2SO plus sucrose were more effective at maintaining the fertilization capacity of spermatozoa post-thawing. Egg cryopreservation was not successful with 0% fertilization observed post-thawing. The results suggest that it is feasible to implement spermatozoa cryopreservation as technological innovation to create a sperm bank for E. lucunter, which can be used in ecotoxicological tests, bringing benefits for researches and contributing to the conservation of the species.

Cryobanking of aquatic species.

This review is focused on the applications of genome cryobanking of aquatic species including freshwater and marine fish, as well as invertebrates. It also reviews the latest advances in cryobanking of model species, widely used by the scientific community worldwide, because of their applications in several fields. The state of the art of cryopreservation of different cellular types (sperm, oocytes, embryos, somatic cells and primordial germ cells or early spermatogonia) is discussed focusing on the advantages and disadvantages of each procedure according to different applications. A special review on the need of standardization of protocols has also been carried out. In summary, this comprehensive review provides information on the practical details of applications of genome cryobanking in a range of aquatic species worldwide, including the cryobanks established in Europe, USA, Brazil, Australia and New Zealand, the species and type of cells that constitute these banks and the utilization of the samples preserved. STATEMENT OF RELEVANCE: This review compiles the last advances on germplasm cryobanking of freshwater and marine fish species and invertebrates, with high value for commercial aquaculture or conservation. It is reviewed the most promising cryopreservation protocols for different cell types, embryos and larvae that could be applied in programs for genetic improvement, broodstock management or conservation of stocks to guarantee culture production.

Can additives ameliorate oxidative stress and improve development of Greenshell mussel (Perna canaliculus) oocytes during cryopreservation?

BACKGROUND: Cryopreservation of P. canaliculus oocytes has not yet been achieved. OBJECTIVE: The present study is to investigate whether the incorporation of: DMSO (0.09%), α-tocopherol (0.1 mM) plus taurine (1 mM) and ethylenediaminetetraacetic acid (EDTA; 0.1 mM), is beneficial during cryopreservation. METHODS: These three additives were incorporated to both the cryoprotectant (CPA) and recovery media, and evaluated in terms of development and oxidative stress at three key stages of cryopreservation: 1) cryoprotectant addition [10% v/v ethylene glycol plus 0.2M trehalose; final concentration], 2) cooling to -6 degrees C, and 3) cooling to -35 degrees C and liquid nitrogen immersion. RESULTS: Over all treatments (including controls) progressive cryopreservation steps resulted in a decrease in fertilization and development to D-larvae, an increase in macromolecular oxidative damage markers (protein carbonyls, lipid hydroperoxides and oxidized DNA), and a decrease in enzymatic (superoxide dismutase, catalase, glutathione S-transferase and glutathione reductase) and non-enzymatic antioxidants. CONCLUSION: Whilst results varied, the major effects of the additives were the improved percentage fertilization and a decrease in macromolecular damage.

Towards cryopreservation of Greenshell mussel (Perna canaliculus) oocytes.

Cryopreservation is a powerful tool for selective breeding in aquaculture as it enables genetic material from selected stock to be stored and crossed at will. The aim of this study was to develop a method for cryopreserving oocytes of the Greenshelltrade mark mussel (Perna canaliculus), New Zealand's main aquaculture species. The ability of oocytes to be fertilized post-thawing was used as the criterion for success in initial experiments and then subsequently, the ability of frozen oocytes to develop further to D-stage larvae was assessed. Ethylene glycol, propylene glycol, dimethyl sulphoxide and glycerol were evaluated at a range of concentrations with and without the addition of 0.2M trehalose using post-thaw fertilization as the endpoint. Ethylene glycol was most effective, particularly when used in combination with trehalose. A more detailed investigation revealed that ethylene glycol at 9% or 10% in the presence of 0.2-0.4M trehalose afforded the best protection. In experiments varying sperm to egg ratio and egg density in post-thaw fertilization procedures, D-larval yield averaged less than 1%. Following these results, a detailed experiment was conducted to determine the damaging steps in the cryopreservation process. Fertilization losses occurred at each step whereas D-larval yield approximately halved following CPA addition and was almost zero following cooling to -10 degrees C. Cryomicroscopy studies and fertilization results suggest that the inability of oocytes to develop to D-larvae stage after cooling to -10 degrees C and beyond are most likely related to some form of chilling injury rather than extracellular ice triggering intracellular ice formation. Further research is needed to determine the causes of this injury and to reduce CPA toxicity and/or osmotic effects.

Cryopreservation of sea urchin sperm and early life stages.

Sea urchins are excellent model organisms useful for several lines of biotechnological research. Sea urchins are typically collected from the sea and kept in research facilities all over the world for such purposes. Cryopreservation can be a very powerful tool to enhance the use of sea urchins as a model species for research. The development of cryopreservation protocols for different sea urchin gametes, embryos, and larvae allows year round access to high quality material outside the natural reproductive season. It also reduces the uncertainty and variability that may be caused by changing oceanic, meteorological, and environmental conditions. Access to cryopreserved gametes and embryos will allow using these model organisms in laboratories all around the world, regardless of their facilities or their proximity to a natural population of sea urchins. Cryopreservation is a very useful tool for aquaculture production, fisheries conservation, and wild stock enhancement allowing spat supply all year round without the need of conditioning broodstock for out of season reproduction-which is expensive, time consuming, and often unfruitful. It will also provide flexibility for selective breeding programs by allowing crossings of individuals with different reproductive seasons. Although cryopreservation protocols have been successfully developed for many valuable fisheries species such as sturgeons, salmonid fishes, and other marine invertebrates (e.g., oysters), only a small amount of research has been carried out regarding sea urchin cryopreservation. In this chapter, we outline protocols for the cryopreservation of sea urchin cells.

Greenshell™ Mussels: A Review of Veterinary Trials and Future Research Directions.

The therapeutic benefits of Greenshell™ mussel (GSM; Perna canaliculus) preparations have been studied using in vitro test systems, animal models, and human clinical trials focusing mainly on anti-inflammatory and anti-arthritic effects. Activity is thought to be linked to key active ingredients that include omega-3 polyunsaturated fatty acids, a variety of carotenoids and other bioactive compounds. In this paper, we review the studies that have been undertaken in dogs, cats, and horses, and outline new research directions in shellfish breeding and high-value nutrition research programmes targeted at enhancing the efficacy of mussel and algal extracts. The addition of GSM to animal diets has alleviated feline degenerative joint disease and arthritis symptoms, and chronic orthopaedic pain in dogs. In horses, GSM extracts decreased the severity of lameness and joint pain and provided improved joint flexion in limbs with lameness attributed to osteoarthritis. Future research in this area should focus on elucidating the key active ingredients in order to link concentrations of these active ingredients with their pharmacokinetics and therapeutic effects. This would enable consistent and improved efficacy from GSM-based products for the purpose of improved animal health.

Docosapentaenoic Acid (22:5n-3) Downregulates mRNA Expression of Pro-inflammatory Factors in LPS-activated Murine Macrophage Like RAW264.7 Cells.

Docosapentaenoic acid (22:5n-3, n-3 DPA) is a n-3 polyunsaturated fatty acid (PUFA) found in fish oil, and has been reported to have health benefits. This study investigated conversion of n-3 DPA, and examined the anti-inflammatory effects of n-3 DPA on activated macrophages. Murine macrophage-like RAW264.7 cells were incubated in culture media containing n-3 DPA for 72 h. The level of n-3 DPA in the fatty acid composition of the total lipid fraction increased in a dose-dependent manner. Furthermore, the levels of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were higher in treated cells than in control cells. In RAW264.7 cells stimulated by lipopolysaccharide (LPS), n-3 DPA significantly down-regulated mRNA expression of pro-inflammatory factors such as IL-6, IL-1ß, iNOS and COX-2. Production of IL-6 was also reduced by n-3 DPA in a dose-dependent manner. We found that n-3 DPA treatment resulted in greater IL-6 mRNA down-regulation than that achieved with EPA treatment, and was similar to that of DHA treatment. Furthermore, expression levels of IL-6 and IL-1ß mRNAs were measured in the presence of the delta-6 desaturase inhibitor SC26196 in the culture medium to inhibit the conversion of n-3 DPA to DHA. There was no significant difference in the down-regulation in the mRNA expression of pro-inflammatory cytokines in RAW264.7 cells by n-3 DPA with or without presence of SC26196. These results demonstrate that n-3 DPA exhibits anti-inflammatory effects in activated RAW264.7 cells, which are independent of DHA conversion.

The effect of external medium composition on membrane water permeability of zebrafish (Danio rerio) embryos.

The effect of external medium composition on chorion and plasma membrane permeability of zebrafish (Danio rerio) embryos was investigated in this study. Initially, survival of embryos spawned into varying strengths (10-40%) of Hank's solution (HBSS) was assessed. Development and hatching rates for embryos spawned into 30% and 40% HBSS were significantly lower than those obtained with embryos spawned into system water. The effect of embryo survival in 30% HBSS with different calcium levels was then investigated. Embryo survival in calcium free 30% HBSS or 30% HBSS with 10x the standard calcium concentration was similar to survival in standard 30% HBSS. Membrane water permeability was determined by measuring the floatation time of embryos in test solutions made up with heavy water (D2O) instead of deionized water. Intact embryos at early developmental stages were less permeable than later stages irrespective of the external medium that they were spawned into. In system water, the floatation time of embryos at one-cell and two-cell stages were 1323+/-83 and 1189+/-55 s, respectively, compared to 432+/-6 and 353+/-10 s at the high and 50% epiboly stages. Change of external medium composition had no effect on membrane permeability of intact embryos at early developmental stages. However, at later stages embryos spawned into 30% HBSS were less permeable than embryos spawned into system water, irrespective of calcium concentration. The flotation time of embryos at the high stage increased from 432+/-6s in system water to 468+/-10s in 30% HBSS. The study on dechorionated embryos showed that change of external medium composition had no effect on plasma membrane permeability.

Cryopreservation of Greenshell™ mussel (Perna canaliculus) sperm.

Cryopreservation is a valuable technique for aquaculture as it enables a library or bank of genetically valuable animals to be maintained in a cost-effective manner. Here, we describe a method to cryopreserve the sperm of the Greenshell™ mussel (Perna canaliculus) and how to use the sperm post-thawing to maximize larval production from thawed sperm in selective breeding.

Cryopreservation of sea urchin (Evechinus chloroticus) sperm.

A method was developed for cryopreserving sperm of the sea urchin, Evechinus chloroticus. Sperm fertilisation ability, mitochondrial function and membrane integrity were assessed before and after cryopreservation. Highest post-thaw fertilisation ability was achieved with lower concentrations (2.5%-7.5%) of dimethyl sulphoxide (DMSO). In contrast, post-thaw mitochondrial function and membrane integrity were higher for sperm frozen in intermediate and high DMSO concentrations (5%-15%). Surprisingly, some sperm frozen in seawater only, without DMSO, were able to survive post-thawing, although the fertilisation ability (10(6) sperm/ml; approximately 50% fertilisation), mitochondrial function and membrane integrity of these sperm were notably lower than of sperm frozen with DMSO (10(6) sperm cells/ml; 2.5%-7.5% DMSO; >85% fertilisation) at the concentrations tested. Amongst sperm from individual males, fertilisation ability varied before and after cryopreservation for both males frozen with and without cryoprotectant. Specific differences among males also varied. Sperm mitochondrial function and membrane integrity was similar among males before cryopreservation but differed considerably after cryopreservation. Cryopreserved sperm were able to fertilise eggs and develop to pluteus stage larvae. This study has practical applications and will provide benefits such as reduced broodstock conditioning costs, control of parental input and opportunities for hybridisation studies.

An investigation of oxidative stress and antioxidant biomarkers during Greenshell mussel (Perna canaliculus) oocyte cryopreservation.

Oxidative damage to proteins and lipids, the enzymatic and nonenzymatic antioxidants' response, and the fertilization and development capability of Perna canaliculus oocytes were investigated at critical treatment steps in a previously published controlled-rate cryopreservation protocol. The cryoprotectant (CPA) from this protocol comprises 10% ethylene glycol (v:v) and 0.2 M trehalose (wt/vol) final concentration. Critical treatment steps included (1) seawater control, (2) CPA addition, (3) CPA addition followed by cooling to -6 °C, (4) CPA addition and cooling to -10 °C, and (5) CPA addition and cooling to -35 °C and immersion in liquid nitrogen (LN). The percentage of fertilized oocytes was 53.8 ± 13.3% in the seawater control but was reduced to 26.0 ± 15.6% after -35 °C + LN treatment, whereas development to D-larvae was 21.0 ± 6.4% in the seawater control reduced to 4.8 ± 2.9% after cooling to -6 °C, and was zero at all the subsequent cooling steps. All oxidative damage biomarkers, protein carbonyls (PCs) and lipid hydroperoxides (LPs), and antioxidants, superoxide dismutase (SOD), catalase, glutathione peroxidase, percent reduced glutathione (%GSH), and total glutathione (defined as glutathione; reduced [GSH] plus glutathione disulphide; derived from two molecules of GSH [GSSG]) were measured over all treatments on unfertilized oocytes over a post-treatment recovery period of 0 to 240 minutes in seawater. An ANOVA showed that both treatment and post-treatment periods had significant effects on the concentrations of all biomarkers (P < 0.05). Protein carbonyls and LPs increased very little after CPA addition and cooling treatments, when compared with the seawater control, but large increases up to sixfold occurred between 0 and 240 minutes for the -35 °C + LN treatment. Concentrations of SOD, catalase, total glutathione, and %GSH at 0 minutes decreased by -31.2%, -26.9%, -21.9%, and -25.0%, respectively, between the seawater control and the -35 °C + LN treatment. In contrast, glutathione peroxidase concentrations at 0 minutes increased by 34.3% between the seawater control and the -35 °C + LN treatment. Although most biochemical biomarkers showed an increasing trend over time (0-240 minutes), total glutathione decreased in concentration over time in all treatments, with the greatest decrease after the -35 °C + LN treatment (-41.2%). Significant correlations between biomarkers and D-larvae yield were negative for LPs and positive for SOD, total glutathione, and %GSH (P < 0.05). This is the first report of an investigation using these oxidative stress biomarkers and antioxidant responses on mussel oocytes, and the results have proved useful in characterizing cellular injury during the cryopreservation process.

The potential for cryopreserving larvae of the sea urchin, Evechinus chloroticus.

Larvae of the sea urchin, Evechinus chloroticus, at varying stages of development, were assessed for their potential to survive cryopreservation. Ethylene glycol (EG) and dimethyl sulphoxide (Me2SO), at concentrations of 1-2 M, were evaluated as cryoprotectants (CPAs) in freezing regimes initially based on methods established for freezing larvae of other sea urchin species. Subsequent work varied cooling rate, holding temperature, holding time, and plunge temperature. Ethylene glycol was less toxic to larvae than Me2SO. However, no larvae survived freezing and thawing in EG. Larvae frozen in Me2SO at the gastrula stage and 4-armed pluteus stage regained motility post-thawing. The most successful freezing regime cooled straws containing larvae in 1.5 M Me2SO from 0 to -35 degrees C at 2.5 degrees C min(-1), held at -35 degrees C for 5 min, then plunged straws into liquid nitrogen. Motility was high 2-4 h post-thawing using this regime but decreased markedly within 24 h. Some 4-armed pluteus larvae that survived beyond this time developed through to metamorphosis and settled. Different Me2SO concentrations and supplementary trehalose did not improve long-term survival. Large variation in post-thaw survival was observed among batches of larvae produced from different females.

Cryopreservation of economically valuable marine micro-algae in the classes Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Haptophyceae, Prasinophyceae, and Rhodophyceae.

The ability to routinely cryopreserve micro-algal species reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. Cryopreservation is also a useful adjunct in aquaculture hatcheries for strains of micro-algae where the nutritional status may change as a result of continuous sub-culture. In this study, cryopreservation of isolates from seven micro-algal classes was investigated. Successful candidates included the marine dinoflagellates Amphidinium carterae, Amphidinium trulla, and Gymnodinium simplex, and the haptophytes Chrysochromulina simplex, Prymnesium parvum, Prymnesium parvum f. patelliferum, Isochrysis galbana, and Pavlova lutheri. Also successfully cryopreserved were the planktonic diatoms Chaetoceros calcitrans, Chaetoceros muelleri, Chaetoceros sp., and the benthic Nitzschia ovalis, the chlorophyte Chlamydomonas coccoides, the rhodophyte Porphyridium purpureum, the prasinophytes Tetraselmis chuii, and Tetraselmis suecica, and the cyanophytes Raphidiopsis sp., and Aphanizomenon flos-aquae. All species were successfully cryopreserved using 15% Me2SO.

Studies on membrane permeability of zebrafish (Danio rerio) oocytes in the presence of different cryoprotectants.

Investigation into fish oocyte membrane permeability is essential for developing successful protocols for their cryopreservation. The aim of the present work was to study the permeability of the zebrafish (Danio rerio) oocyte membrane to water and cryoprotectants before cryopreservation protocol design. The study was conducted on stage III and stage V zebrafish oocytes. Volumetric changes of stage III oocytes in different concentrations of sucrose were measured after 20 min exposure at 22 degrees C and the osmotically inactive volume of the oocytes (Vb) was determined using the Boyle-van't Hoff relationship. Volumetric changes of oocytes during exposure to different cryoprotectant solutions were also measured. Oocytes were exposed to 2 M dimethyl sulphoxide (DMSO), propylene glycol (PG), and methanol for 40 min at 22 degrees C. Stage III oocytes were also exposed to 2 M DMSO at 0 degrees C. Oocyte images were captured on an Olympus BX51 cryomicroscope using Linkham software for image recording. Scion Image was used for image analysis and diameter measurement. The experimental data were fitted to a two-parameter model using Berkeley Madonna 8.0.1 software. Hydraulic conductivity (L(p)) and solute (cryoprotectant) permeability (Ps) were estimated using the model. The osmotically inactive volume of stage III zebrafish oocytes was found to be 69.5%. The mean values+/-SE of Lp were found to be 0.169+/-0.02 and 0.196+/-0.01 microm/min/atm in the presence of DMSO and PG, respectively, at 22 degrees C, assuming an internal isosmotic value for the oocyte of 272 mOsm. The Ps values were 0.000948+/-0.00015 and 0.000933+/-0.00005 cm/min for DMSO and PG, respectively. It was also shown that the membrane permeability of stage III oocytes decreased significantly with temperature. No significant changes in cell volume during methanol treatment were observed. Fish oocyte membrane permeability parameters are reported here for the first time. The Lp and Ps values obtained for stage III zebrafish oocytes are generally lower than those obtained from successfully cryopreserved mammalian oocytes and higher than those obtained with fish embryos and sea urchin eggs. It was not possible to estimate membrane permeability parameters for stage V oocytes using the methods employed in this study because stage V oocytes experienced the separation of outer oolemma membrane from inner vitelline during exposure to cryoprotectants.

Membrane permeability characteristics and osmotic tolerance limits of sea urchin (Evechinus chloroticus) eggs.

Development of effective cryopreservation protocols relies on knowledge of the fundamental cryobiological characteristics for a particular cell type. These characteristics include osmotic behaviour, membrane permeability characteristics, and osmotic tolerance limits. Here, we report on measures of these characteristics for unfertilized and fertilised eggs of the sea urchin (Evechinus chloroticus). In NaCl solutions of varying osmolalities, sea urchin eggs behaved as ideal linear osmometers. The osmotically inactive volume (vb) was similar for unfertilized and fertilised eggs, 0.367+/-0.008 (mean+/-SE) and 0.303+/-0.007, respectively. Estimates of water solubility (Lp) and solute permeability (Ps) and their respective activation energies (Ea) for unfertilized and fertilised eggs were determined following exposure to cryoprotectant (CPA) solutions at different temperatures. Irrespective of treatment, fertilised eggs had higher values of Lp and Ps. The presence of a CPA decreased Lp. Among CPAs, solute permeability was highest for propylene glycol followed by dimethyl sulphoxide and then ethylene glycol. Measures of osmotic tolerance limits of the eggs revealed unfertilized eggs were able to tolerate volumetric changes of -20% and +30% of their equilibrium volume; fertilised eggs were able to tolerate changes +/-30%. Using membrane permeability data and osmotic tolerance limits, we established effective methods for loading and unloading CPAs from the eggs. The results of this study establish cryobiological characteristics for E. chloroticus eggs of use for developing an effective cryopreservation protocol. The approach we outline can be readily adapted for determining cryobiological characteristics of other species and cell types, as an aid to successful cryopreservation.