Abstract
Simple SummaryIn vertebrates, thyroid hormones, triiodothyronine, and thyroxine play a pivotal role in regulating development, metamorphosis, and metabolism. Recently, the presence of endogenous thyroid hormone signaling has also been reported in invertebrates. We assayed thyroid hormone profiles in the red king crab, an iconic commercially important species, which was introduced into the Barents Sea in the 1960s and now is supporting a large-scale profitable fishery. Both thyroid hormones were detected in the crab hemolymph. Their levels fluctuated significantly depending on the maturity status of the crabs and sampling season. These findings confirm that thyroid hormones are involved in the specific physiological processes of red king crabs and may be used in aquaculture.Only a few studies have reported the presence and levels of thyroid hormones in invertebrates. At the same time, the administration of these hormones has been shown to be a profitable method for inducing growth in crustaceans. Knowledge of thyroid hormone concentrations is required to involve this approach in crustacean aquaculture. For this reason, we examined hemolymph samples of the invasive red king crab Paralithodes camtschaticus from the Barents Sea population for the levels of triiodothyronine (T3) and thyroxine (T4). Radioimmunoassays indicated that T3 ranged from 0.26 to 1.55 μg dL–1, whereas T4 varied from 52 to 203 μg dL–1. Adult crabs demonstrated higher levels of T3 than juveniles, while juvenile crabs had higher levels of T4 in comparison to larger conspecifics. The thyroxine levels were consistent throughout the study period. In contrast, significant seasonal variations were found for T3. In immature crabs, the maximum concentration was found in October, whereas in adult crabs, the highest level of T3 was registered in August. Most likely, these results are explained by changes in physiological conditions of the crabs associated with their molting calendar and migration activity. Our data may have important implications for aquaculture of Paralithodes camtschaticus in the Barents Sea.
Highlights
Triiodothyronine is the biologically active hormone, whereas thyroxine, the major thyroid hormone that is secreted from the thyroid gland consisting of follicles, is a precursor or prohormone
Iromo et al [11] studied thyroxin concentrations in hemolymph of female mud crabs of Scylla serrata from Tarakan Island, East Borneo, Indonesia, and found that immature crabs exhibited the lowest concentration of T4 (8.50 ± 2.17 ng mL–1 ), maturing crabs have the intermediate level of T4 (11.23 ± 2.06 ng mL–1 ), and the highest concentration was found in ripe females (15.33 ± 7.20 ng mL–1 )
Our data indicate that the hemolymph of adult crabs contains more triiodothyronine than juveniles, while immature crabs demonstrate higher thyroxine concentrations than mature individuals
Summary
There are two main thyroid hormones: 30 ,50 ,3,5-L-tetraiodothyronine (thyroxine), which is nowadays commonly called T4, and 30 ,5,3-L-triiodothyronine, T3 [1]. These hormones are composed of two tyrosyl residues linked through an ether linkage and substituted with 4 or 3 iodine residues, respectively. Non-vertebrate chordates, such as tunicates, cephalochordates, and the larvae of lampreys have the endostyle, which acts as a thyroid gland homolog [7,8]. Non-chordate invertebrates without thyroid follicles have been shown to accumulate iodo-compounds exogenously from seawater and through diets containing micro- and macroalgae [9]. Because thyroid hormones are able to affect reproduction processes in invertebrates, these substances are considered promising agents in shellfish aquaculture [14,15,16]
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