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Key Event Title
Reduced, Posterior swim bladder inflation
Key Event Components
|swim bladder inflation||posterior chamber swim bladder||decreased|
Key Event Overview
AOPs Including This Key Event
Key Event Description
The teleost swim bladder is a gas-filled structure that consists of two chambers, the posterior and anterior chamber. In zebrafish, the posterior chamber inflates around 96-120 h post fertilization (hpf) which is 2-3 days post hatch, and the anterior chamber inflates around 21 dpf (days post fertilization). In fathead minnow, the posterior and anterior chamber inflate around 6 and 14 dpf respectively.
The posterior chamber is formed from a bud originating from the foregut endoderm (Winata et al., 2009). The posterior chamber operates as a hydrostatic organ. The volume of gas in the adult swim bladder is continuously adjusted to regulate body density and buoyancy.
Many amphibians and frogs go through an embryo-larval transition phase marking the switch from endogenous feeding (from the yolk) to exogenous feeding. In zebrafish, embryonic-to-larval transition takes place around 96 hours post fertilization (hpf). As in amphibians, the transition between the different developmental phases includes maturation and inflation of the swim bladder (Liu and Chan, 2002).
Reduced inflation of the posterior chamber may manifest itself as either a complete failure to inflate the chamber or a reduced size of the chamber.
How It Is Measured or Detected
In several fish species, inflation of the posterior chamber can easily be observed using a stereomicroscope because the larvae are still transparent during those early developmental stages. This is for example true for zebrafish and fathead minnow. Posterior chamber size can then be measured based on photographs with a calibrator.
When observing effects on swim bladder inflation, it is important to verify that reduced swim bladder inflation occurs at concentrations significantly lower than those causing mortality, since a wide variety of chemicals cause impaired posterior chamber inflation at exposure concentrations that also cause mortality (Stinckens et al., 2018).
Domain of Applicability
Taxonomic: Teleost fish can be divided in two groups according to swim bladder morphology: physoclistous (e.g., yellow perch, sea bass, striped bass) and physostomous (e.g., zebrafish and fathead minnow). Physostomous fish retain a duct between the digestive tract and the swim bladder during adulthood allowing them to gulp air at the surface to fill the swim bladder. In contrast, in physoclistous fish, once initial inflation by gulping atmospheric air at the water surface has occurred, the swim bladder is closed off from the digestive tract and swim bladder volume is regulated by gas secretion into the swim bladder (Wooley and Qin, 2010). Much of the evidence for impaired posterior chamber of the swim bladder currently comes from work on zebrafish and fathead minnow (Stinckens et al., 2018; Cavallin et al., 2017; Wang et al., 2020). Increasing evidence is becoming available on defects of swim bladder inflation in Medala (Oryzias latipes) (Gonzalez-doncel et al., 2003; Dong et al., 2016; Kupsco et al., 2016; Mu et al., 2018; Pandelides et al., 2021). This KE is plausibly applicable across fish species with swim bladders, both physostomous and physoclistous.
Life stage: The posterior chamber inflates during a specific developmental time frame. In zebrafish, the posterior chamber inflates around 96-120 hpf which is 2-3 dph. In the fathead minnow, the posterior chamber inflates around 6 dpf. Therefore this KE is only applicable to the embryonic life stage.
Sex: This KE/KER is plausibly applicable to both sexes. Sex differences are not often investigated in tests using early life stages of fish. In Medaka, sex can be morphologically distinguished as soon as 10 days post fertilization. Females appear more susceptible to thyroid‐induced swim bladder dysfunction compared with males (Godfrey et al., 2019). In zebrafish and fathead minnow, it is currently unclear whether sex-related differences are important in determining the magnitude of the changes in this KE/KER. Zebrafish are undifferentiated gonochorists since both sexes initially develop an immature ovary (Maack and Segner, 2003). Immature ovary development progresses until approximately the onset of the third week. Later, in female fish immature ovaries continue to develop further, while male fish undergo transformation of ovaries into testes. Final transformation into testes varies among male individuals, however finishes usually around 6 weeks post fertilization. Since the posterior chamber inflates around 5 days post fertilization in zebrafish, when sex differentiation has not started yet, sex differences are expected to play a minor role. Fathead minnow gonad differentiation also occurs during larval development. Fathead minnows utilize a XY sex determination strategy and markers can be used to genotype sex in life stages where the sex is not yet clearly defined morphologically (Olmstead et al., 2011). Ovarian differentiation starts at 10 dph followed by rapid development (Van Aerle et al., 2004). At 25 dph germ cells of all stages up to the primary oocytes stage were present and at 120 dph, vitellogenic oocytes were present. The germ cells (spermatogonia) of the developing testes only entered meiosis around 90–120 dph. Mature testes with spermatozoa are present around 150 dph. Since the posterior chamber inflates around 6 days post fertilization (1 dph) in fathead minnows, sex differences are expected to play a minor role in the current AOP.
Cavallin, J.E., Ankley, G.T., Blackwell, B.R., Blanksma, C.A., Fay, K.A., Jensen, K.M., Kahl, M.D., Knapen, D., Kosian, P.A., Poole, S.T., Randolph, E.C., Schroeder, A.L., Vergauwen, L., Villeneuve, D.L., 2017. Impaired swim bladder inflation in early life stage fathead minnows exposed to a deiodinase inhibitor, iopanoic acid. Environmental Toxicology and Chemistry 36, 2942-2952.
Dong W, Liu J, Wei LX, Yang JF, Chernick M, Hinton DE. 2016. Developmental toxicity from exposure to various forms of mercury compounds in medaka fish (oryzias latipes) embryos. Peerj. 4.
Godfrey A, Hooser B, Abdelmoneim A, Sepulveda MS. 2019. Sex-specific endocrine-disrupting effects of three halogenated chemicals in japanese medaka. Journal of Applied Toxicology. 39(8):1215-1223.
Gonzalez-Doncel M, de la Pena E, Barrueco C, Hinton DE. 2003. Stage sensitivity of medaka (oryzias latipes) eggs and embryos to permethrin. Aquatic Toxicology. 62(3):255-268.
Kupsco A, Schlenk D. 2016. Stage susceptibility of japanese medaka (oryzias latipes) to selenomethionine and hypersaline developmental toxicity. Environmental Toxicology and Chemistry. 35(5):1247-1256.
Liu, Y.W., Chan, W.K., 2002. Thyroid hormones are important for embryonic tolarval transitory phase in zebrafish. Differentiation 70, 36–45, http://dx.doi.org/10.1046/j.1432-0436.2002.700104.x.
Maack, G., Segner, H., 2003. Morphological development of the gonads in zebrafish. Journal of Fish Biology 62, 895-906.
Mu JL, Chernick M, Dong W, Di Giulio RT, Hinton DE. 2017. Early life co-exposures to a real-world pah mixture and hypoxia result in later life and next generation consequences in medaka (oryzias latipes). Aquatic Toxicology. 190:162-173.
Nagabhushana A, Mishra RK. 2016. Finding clues to the riddle of sex determination in zebrafish. Journal of Biosciences. 41(1):145-155.
Olmstead AW, Villeneuve DL, Ankley GT, Cavallin JE, Lindberg-Livingston A, Wehmas LC, Degitz SJ. 2011. A method for the determination of genetic sex in the fathead minnow, pimephales promelas, to support testing of endocrine-active chemicals. Environmental Science & Technology. 45(7):3090-3095.
Pandelides Z, Ussery EJ, Overturf MD, Guchardi J, Holdway DA. 2021. Inhibition of swim bladder inflation in japanese medaka (oryzias latipes) embryos following exposure to select pharmaceuticals alone and in combination. Aquatic Toxicology. 234.
Stinckens, E., Vergauwen, L., Ankley, G.T., Blust, R., Darras, V.M., Villeneuve, D.L., Witters, H., Volz, D.C., Knapen, D., 2018. An AOP-based alternative testing strategy to predict the impact of thyroid hormone disruption on swim bladder inflation in zebrafish. Aquatic Toxicology 200, 1-12.
van Aerle R, Runnalls TJ, Tyler CR. 2004. Ontogeny of gonadal sex development relative to growth in fathead minnow. Journal of Fish Biology. 64(2):355-369.
Wang, J.X., Shi, G.H., Yao, J.Z., Sheng, N., Cui, R.N., Su, Z.B., Guo, Y., Dai, J.Y., 2020. Perfluoropolyether carboxylic acids (novel alternatives to PFOA) impair zebrafish posterior swim bladder development via thyroid hormone disruption. Environment International 134.
Winata, C.L., Korzh, S., Kondrychyn, I., Zheng, W., Korzh, V., Gong, Z., 2009.Development of zebrafish swimbladder: the requirement of Hedgehogsignaling in specification and organization of the three tissue layers. Dev. Biol.331, 222–236, http://dx.doi.org/10.1016/j.ydbio.2009.04.035.
Woolley, L.D., Qin, J.G., 2010. Swimbladder inflation and its implication to the culture of marine finfish larvae. Reviews in Aquaculture 2, 181-190.