Effect of Ca2+ on survival and development of metamorphosing bonefish (Albula sp.) leptocephali |
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Authors: | E Pfeiler |
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Institution: | (1) Departamento de Ciencias Marinas, Instituto Tecnológico y de Estudios Superiores de Monterrey (ITESM), Campus Guaymas, Apartado Postal 484, Guaymas, Sonora 85400, Mexico, MX |
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Abstract: | Bonefish (Albula sp.) larvae (leptocephali) from the Gulf of California complete metamorphosis in ˜10 d in natural seawater (35‰S; Ca2+ conc = 10.5 mM). The increase in ossification that occurs near the end of the non-feeding metamorphic period, in addition to the ability
of larvae to complete metamorphosis in dilute seawater (8‰ S) prompted the present study, where the effects of varying the
external calcium ion concentration, Ca2+]e, of artificial seawater (ASW) on the survival, development and internal (whole-body) calcium ion content, (Ca2+)i, of unfed metamorphosing larvae were investigated. Early-metamorphosing larvae placed in␣ASW, where Ca2+]e = 10.1 mM, survived for up to 10 d and developed normally without exogenous nutrients. In shorter-term experiments (4 to 5 d), no differences
in survival were found for larvae in ASW with Ca2+]e rang-ing from 1.5 to 10.1 mM. However, in Ca2+-free ASW, most larvae died within 27 h and no larvae survived more than 42 h; the median lethal time (LT50), and its 95% confidence limits, were 14.5 (10.0 to 20.9) h. High mortality (81% after 20 h) also occurred in 1.0 mM Ca2+ ASW, but 2 of 16 larvae tested survived for 96 h. The 96 h median tolerance limit (TLM), corrected for control mortality, was 1.2 mM Ca2+. In natural seawater, larval (Ca2+)i remained relatively constant ( = 0.419 mg larva−1)␣in early- and intermediate-metamorphosing larvae, and then increased to a mean value of 0.739 mg larva−1 in advanced larvae, indicating that Ca2+ was␣taken up from the medium at this stage; the increase in (Ca2+)i corresponded to the period of ossification of the vertebral column. Internal (whole-body) magnesium ion content (Mg2+)i showed no significant change during metamorphosis ( = 0.089 mg larva−1). No significant differences in (Ca2+)i were found in advanced larvae in natural seawater and those in ASW, with Ca2+]e ranging from 2.0 to 10.1 mM. However, clearing and staining revealed that ossification of the vertebral column had not yet occurred in advanced larvae
from 2.0 to 10.1 mM Ca2+ ASW. Also, low Ca2+]e (1.0 to 2.0 mM) usually produced deformed larvae that swam erratically, at times showing “whirling” behavior.
Received: 21 August 1996 / Accepted: 26 August 1996 |
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