Low-cost aquatic lab animal holding system

Fish Hacks: Hybridizing Stand-Alone Zebrafish System Plumbing and Pumps to Extend and Improve Function

One of the greatest expenses in running a zebrafish laboratory is the aquatic systems used for housing. These critical pieces of equipment are essential and incorporate components undergoing constant activity in pumping water, monitoring, dosing, and filtration. The systems available on the market are robust, yet ongoing activity eventually leads to the need for repair or replacement. Moreover, some systems are no longer commercially available, impairing the ability to service this critical infrastructure. In this study, we demonstrate a do it yourself (DIY) method to re-engineer an aquatic system's pumps and plumbing, which hybridizes a system no longer commercially available with components used by active vendors. This transition from a two external pump Aquatic Habitat/Pentair design to an individual submerged pump Aquaneering-like plan saves funds by expanding infrastructure longevity. Our hybridized configuration has been in uninterrupted use for >3 years, supporting zebrafish health and high fecundity.

Physiological responses of three species of unionid mussels to intermittent exposure to elevated carbon dioxide

Freshwater systems are at risk owing to increasing carbon dioxide (CO₂) levels, and one of the possible reasons for these elevations is the deployment of non-physical fish barriers to prevent invasive fish movements. Carbon dioxide barriers have the potential to create short, chronic and intermittent exposures of CO₂ for surrounding freshwater biota. Although intermittent exposures to a stressor may be more ecologically relevant, the majority of laboratory tests use chronic or short-term time periods to determine how organisms will respond to an environmental stressor. Measurements of the physiological responses of three species of unionid mussel, giant floaters (Pyganodon grandis), threeridge (Amblema plicata) and plain pocketbook (Lampsilis cardium), exposed to control pCO₂ (~1000 µatm) or intermittent conditions of pCO₂ (ranging from ~1000 to ~55 000 µatm) 12 times per day over a 28 day period were gathered. There was no indication of recovery in the physiological responses of mussels between applications of CO₂, suggesting that the recovery time between CO₂ pulses (1.5 h) was not sufficient for recovery from the CO₂ exposure period (0.5 h). Observations of acid-base and stress responses were consistent with what has been observed in chronic studies of freshwater mussels exposed to elevated pCO₂ (i.e. elevations in HCO₃^-, Ca²⁺, Na⁺ and glucose, and decreases in Mg²⁺ and Cl^-). However, species differences were observed across almost all variables measured, which emphasizes the need for multispecies studies.

Zebrafish Sensitivity to Botulinum Neurotoxins

Botulinum neurotoxins (BoNT) are the most potent known toxins. The mouse LD₅₀ assay is the gold standard for testing BoNT potency, but is not sensitive enough to detect the extremely low levels of neurotoxin that may be present in the serum of sensitive animal species that are showing the effects of BoNT toxicity, such as channel catfish affected by visceral toxicosis of catfish. Since zebrafish are an important animal model for diverse biomedical and basic research, they are readily available and have defined genetic lines that facilitate reproducibility. This makes them attractive for use as an alternative bioassay organism. The utility of zebrafish as a bioassay model organism for BoNT was investigated. The 96 h median immobilizing doses of BoNT/A, BoNT/C, BoNT/E, and BoNT/F for adult male Tübingen strain zebrafish (0.32 g mean weight) at 25 °C were 16.31, 124.6, 4.7, and 0.61 picograms (pg)/fish, respectively. These findings support the use of the zebrafish-based bioassays for evaluating the presence of BoNT/A, BoNT/E, and BoNT/F. Evaluating the basis of the relatively high resistance of zebrafish to BoNT/C and the extreme sensitivity to BoNT/F may reveal unique functional patterns to the action of these neurotoxins.

Zebrafish (Danio rerio) bioassay for visceral toxicosis of catfish and botulinum neurotoxin serotype E

Visceral toxicosis of catfish (VTC), a sporadic disease of cultured channel catfish ( Ictalurus punctatus) often with high mortality, is caused by botulinum neurotoxin serotype E (BoNT/E). Presumptive diagnosis of VTC is based on characteristic clinical signs and lesions, and the production of these signs and mortality after sera from affected fish is administered to sentinel catfish. The diagnosis is confirmed if the toxicity is neutralized with BoNT/E antitoxin. Because small catfish are often unavailable, the utility of adult zebrafish ( Danio rerio) was evaluated in BoNT/E and VTC bioassays. Channel catfish and zebrafish susceptibilities were compared using trypsin-activated BoNT/E in a 96-hr trial by intracoelomically administering 0, 1.87, 3.7, 7.5, 15, or 30 pg of toxin per gram of body weight (g-bw) of fish. All of the zebrafish died at the 7.5 pg/g-bw and higher, while the catfish died at the 15 pg/g-bw dose and higher. To test the bioassay, sera from VTC-affected fish or control sera were intracoelomically injected at a dose of 10 µl per zebrafish and 20 µl/g-bw for channel catfish. At 96 hr post-injection, 78% of the zebrafish and 50% of the catfish receiving VTC sera died, while no control fish died. When the VTC sera were preincubated with BoNT/E antitoxin, they became nontoxic to zebrafish. Histology of zebrafish injected with either VTC serum or BoNT/E demonstrated renal necrosis. Normal catfish serum was toxic to larval zebrafish in immersion exposures, abrogating their utility in VTC bioassays. The results demonstrate bioassays using adult zebrafish for detecting BoNT/E and VTC are sensitive and practical.

Evaluation of visible implant elastomer tags in zebrafish (Danio rerio)

The use of the visible implant elastomer (VIE) tagging system in zebrafish (Danio rerio) was examined. Two tag orientations (horizontal and vertical) at the dorsal fin base were tested for tag retention, tag fragmentation and whether VIE tags affected growth and survival of juvenile zebrafish (1–4 month post hatch). Six tag locations (abdomen, anal fin base, caudal peduncle, dorsal fin base, pectoral fin base, isthmus) and 5 tag colors (yellow, red, pink, orange, blue) were evaluated for ease of VIE tag application and tag visibility in adult zebrafish. Long-term retention (1 year) and multiple tagging sites (right and left of dorsal fin and pectoral fin base) were examined in adult zebrafish. Lastly, survival of recombination activation gene 1^−/− (rag1^−/−) zebrafish was evaluated after VIE tagging.

The best tag location was the dorsal fin base, and the most visible tag color was pink. Growth rate of juvenile zebrafish was not affected by VIE tagging. Horizontal tagging is recommended in early stages of fish growth (1–2 months post hatch). VIE tags were retained for 1 year and tagging did not interfere with long-term growth and survival. There was no mortality associated with VIE tagging in rag1^−/− zebrafish.

The VIE tagging system is highly suitable for small-sized zebrafish. When familiar with the procedure, 120 adult zebrafish can be tagged in one hour. It does not increase mortality in adult zebrafish or interfere with growth in juvenile or adult zebrafish.

Characterization of rag1 mutant zebrafish leukocytes

Background

Zebrafish may prove to be one of the best vertebrate models for innate immunology. These fish have sophisticated immune components, yet rely heavily on innate immune mechanisms. Thus, the development and characterization of mutant and/or knock out zebrafish are critical to help define immune cell and immune gene functions in the zebrafish model. The use of Severe Combined Immunodeficient (SCID) and recombination activation gene 1 and 2 mutant mice has allowed the investigation of the specific contribution of innate defenses in many infectious diseases. Similar zebrafish mutants are now being used in biomedical and fish immunology related research. This report describes the leukocyte populations in a unique model, recombination activation gene 1^-/- mutant zebrafish (rag1 mutants).

Results

Differential counts of peripheral blood leukocytes (PBL) showed that rag1 mutants had significantly decreased lymphocyte-like cell populations (34.7%) compared to wild-types (70.5%), and significantly increased granulocyte populations (52.7%) compared to wild-types (17.6%). Monocyte/macrophage populations were similar between mutants and wild-types, 12.6% and 11.3%, respectively. Differential leukocyte counts of rag1 mutant kidney hematopoietic tissue showed a significantly reduced lymphocyte-like cell population (8%), a significantly increased myelomonocyte population (57%), 34.8% precursor cells, and 0.2% thrombocytes, while wild-type hematopoietic kidney tissue showed 29.4% lymphocytes/lymphocyte-like cells, 36.4% myelomonocytes, 33.8% precursors and 0.5% thrombocytes.

Flow cytometric analyses of kidney hematopoietic tissue revealed three leukocyte populations. Population A was monocytes and granulocytes and comprised 34.7% of the gated cells in rag1 mutants and 17.6% in wild-types. Population B consisted of hematopoietic precursors, and comprised 50% of the gated cells for rag1 mutants and 53% for wild-types. Population C consisted of lymphocytes and lymphocyte-like cells and comprised 7% of the gated cells in the rag1 mutants and 26% in the wild-types.

Reverse transcriptase polymerase chain reaction (RT-PCR) assays demonstrated rag1 mutant kidney hematopoietic tissue expressed mRNA encoding Non-specific Cytotoxic cell receptor protein-1 (NCCRP-1) and Natural Killer (NK) cell lysin but lacked T cell receptor (TCR) and immunoglobulin (Ig) transcript expression, while wild-type kidney hematopoietic tissue expressed NCCRP-1, NK lysin, TCR and Ig transcript expression.

Conclusion

Our study demonstrates that in comparison to wild-type zebrafish, rag1 mutants have a significantly reduced lymphocyte-like cell population that likely includes Non-specific cytotoxic cells (NCC) and NK cells (and lacks functional T and B lymphocytes), a similar macrophage/monocyte population, and a significantly increased neutrophil population. These zebrafish have comparable leukocyte populations to SCID and rag 1 and/or 2 mutant mice, that possess macrophages, natural killer cells and neutrophils, but lack T and B lymphocytes. Rag1 mutant zebrafish will provide the platform for remarkable investigations in fish and innate immunology, as rag 1 and 2 mutant mice did for mammalian immunology.

Zebrafish kidney phagocytes utilize macropinocytosis and Ca+-dependent endocytic mechanisms

Background

The innate immune response constitutes the first line of defense against invading pathogens and consists of a variety of immune defense mechanisms including active endocytosis by macrophages and granulocytes. Endocytosis can be used as a reliable measure of selective and non-selective mechanisms of antigen uptake in the early phase of an immune response. Numerous assays have been developed to measure this response in a variety of mammalian and fish species. The small size of the zebrafish has prevented the large-scale collection of monocytes/macrophages and granulocytes for these endocytic assays.

Methodology/Principal Findings

Pooled zebrafish kidney hematopoietic tissues were used as a source of phagocytic cells for flow-cytometry based endocytic assays. FITC-Dextran, Lucifer Yellow and FITC-Edwardsiella ictaluri were used to evaluate selective and non-selective mechanisms of uptake in zebrafish phagocytes.

Conclusions/Significance

Zebrafish kidney phagocytes characterized as monocytes/macrophages, neutrophils and lymphocytes utilize macropinocytosis and Ca²⁺-dependant endocytosis mechanisms of antigen uptake. These cells do not appear to utilize a mannose receptor. Heat-killed Edwardsiella ictaluri induces cytoskeletal interactions for internalization in zebrafish kidney monocytes/macrophages and granulocytes. The proposed method is easy to implement and should prove especially useful in immunological, toxicological and epidemiological research.