Osmolarity and composition of cell culture media affect further development and survival in zebrafish embryos

Ontogenetic Changes in Blood Osmolality During the Postembryonic Development of Zebrafish (Danio rerio)

The zebrafish Danio rerio is a teleost model species widely used in developmental genetics, biomedical studies, toxicology, and drug screening. Despite the interest of this species in research, little is known through indirect observations about its blood osmolality, which is a key parameter for diverse experiments. In this study, we directly measured blood osmolality using nano-osmometry at different stages of zebrafish postembryonic development. We found that blood osmolality is close to 240 mOsm·kg⁻¹ in early larvae. It progressively increased to ∼270 mOsm·kg⁻¹ during the larval development before reaching ∼300 mOsm·kg⁻¹ after metamorphosis in juveniles and later in adults. These ontogenetic changes in blood osmolality illustrate the physiological changes in osmoregulation associated with postembryonic development, including metamorphosis. These values are of practical interest for adjusting the osmolality of fixatives and cell and tissue culture media for research using zebrafish as a model.

Reduction in activity by noxious chemical stimulation is ameliorated by immersion in analgesic drugs in zebrafish

Research has recently demonstrated that larval zebrafish show similar molecular responses to nociception to those of adults. Our study explored whether unprotected larval zebrafish exhibited altered behaviour after exposure to noxious chemicals and screened a range of analgesic drugs to determine their efficacy to reduce these responses. This approach aimed to validate larval zebrafish as a reliable replacement for adults as well as providing a high-throughput means of analysing behavioural responses. Zebrafish at 5 days post-fertilization were exposed to known noxious stimuli: acetic acid (0.01%, 0.1% and 0.25%) and citric acid (0.1%, 1% and 5%). The behavioural response of each was recorded and analysed using novel tracking software that measures time spent active in 25 larvae at one time. Subsequently, the efficacy of aspirin, lidocaine, morphine and flunixin as analgesics after exposure to 0.1% acetic acid was tested. Larvae exposed to 0.1% and 0.25% acetic acid spent less time active, whereas those exposed to 0.01% acetic acid and 0.1–5% citric acid showed an increase in swimming activity. Administration of 2.5 mg l−1 aspirin, 5 mg l−1 lidocaine and 48 mg l−1 morphine prevented the behavioural changes induced by acetic acid. These results suggest that larvae respond to a noxious challenge in a similar way to adult zebrafish and other vertebrates and that the effect of nociception on activity can be ameliorated by using analgesics. Therefore, adopting larval zebrafish could represent a direct replacement of a protected adult fish with a non-protected form in pain- and nociception-related research.

Ultraviolet radiation and handling medium osmolarity affect chimaerism success in zebrafish

The effects of a predefined ultraviolet radiation dose (0.529 mW/cm2 for 30s) together with two different micromanipulation medium osmolarities (30 mOsm/kg vs 300 mOsm/kg) were tested on embryo survival at different developmental stages and on the somatic (skin) and germ-line chimaerism rates. Somatic (13%, 6/47 adults) and germ-line chimaerism (50% pigmented F1 larvae) were detected only in the UV-treated recipient embryos micromanipulated in a 300 mOsm/kg medium. From the results obtained, we concluded that the conditions cited above were the most suitable to improve somatic and germ-line chimaerism rates in zebrafish.

Micromanipulation medium osmolarity compromises zebrafish (Danio rerio) embryo and cell survival in chimaerism experiments

In zebrafish chimaerism experiments, the cell injection can involve intra-embryonic cell lyses by osmolar effects. Moreover, the donor cells can be injured during manipulation due to osmolar changes into the transplant pipette. Therefore, the present study aimed to assess the effects of manipulation medium osmolarity on embryonic survival and donor cell viability.In Experiment I, 0.1 microl to 0.15 microl approximately of an isosmolar solution (300 mOsm) was injected into recipient embryos, which were kept at 300 (E1) or 30 mOsm (E2). Survival at day 1 was significantly higher in the E2 group than in E1 (E1: 68% vs E2: 81%, p < 0.05), but after 5 days embryo survival in the E1 group was slightly higher. In Experiment II, donor cells from zebrafish embryos were exposed (or not) to a possible osmolarity change (inner pipette medium: 300 mOsm vs external medium: 30 or 300 mOsm) using two different micropipette outer diameters, 40-50 and 60-70 microm. Cell mechanical damage was detected in the 40-50 microm pipette (p < 0.05), but not by the handling medium osmolarity. Results recommend the use of a 300 mOsm manipulation medium and bore-sized pipettes adjusted as closely as possible to the donor cell size.