Abstract :
[en] The sheepshead minnow is widely used in
ecotoxicological studies that only recently have begun
to focus on disruption of the thyroid axis by xenobiotics
and endocrine disrupting compounds. However, reference
levels of the thyroid prohormone thyroxine (T4)
and biologically active hormone 3,5,30-triiodothyronine
(T3) and their developmental patterns are
unknown. This study set out to describe the ontogeny
and morphology of the thyroid gland in sheepshead
minnow, and to correlate these with whole-body
concentrations of thyroid hormones during early
development and metamorphosis. Eggs were collected
by natural spawning in our laboratory. T4 and T3 were
extracted from embryos, larvae and juveniles and an
enzyme-linked immunoassay was used to measure
whole-body hormone levels. Length and body mass,
hatching success, gross morphology, thyroid hormone
levels and histology were measured. The onset of
metamorphosis at 12-day post-hatching coincided with
surges in whole-body T4 and T3 concentrations.
Thyroid follicles were first observed in pre-metamorphic
larvae at hatching and were detected exclusively in
the subpharyngeal region, surrounding the ventral
aorta. Follicle size and thyrocyte epithelial cell heights
varied during development, indicating fluctuations in
thyroid hormone synthesis activity. The increase in the
whole-body T3/T4 ratio was indicative of an increase in
outer ring deiodination activity. This study establishes a
baseline for thyroid hormones in sheepshead minnows,
which will be useful for the understanding of thyroid
hormone functions and in future studies of thyroid
toxicants in this species.
Scopus citations®
without self-citations
9
