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Concentrations of selenium have been reported in the tissues of sturgeon species at levels that can cause adverse morphological defects. Pallid sturgeon (Scaphirhynchus albus), a federally listed endangered species, and shovelnose sturgeon (Scaphirhynchus platorynchus) populations are declining. Fish species are known to be sensitive to elevated selenium concentrations during larval stages. Exposure to selenium can be caused through contaminated water and through the diet. Additionally, females can maternally transfer selenium to their eggs. We wanted to determine if increased levels of selenium in the eggs of sturgeon cause effects such as scoliosis, deformities of the skull, and shortened snout detectable at early life stages to mimic the effects of maternally transferred selenium to eggs of pallid and shovelnose sturgeon. Newly fertilized eggs were injected with 0 µg (control), 8.4 µg (low), 16.8 µg (medium), or 25.5 µg (high) doses of selenium (as selenomethionine) per gram of egg. Young sturgeons were sacrificed and preserved in neutral buffered formalin at varying time points and later observed intact or cleared and stained to observe bones and cartilage. We made up to seven measurements on the dorsal and ventral sides of the heads of 22-24 day old sturgeon exposed to the various concentrations of selenium and those unexposed (control). Bodies of the sturgeon were checked for any noticeable curvature. Measurements were made on mandible, snout, and maxilla lengths to determine the severity of deformity attributed to selenium.
Results/Conclusions
Cleared larval sturgeon (5-6 days old) showed only cartilage and no bone development in the head. Bone was not detected until sturgeon were 22-24 days old. Means of all measurements were numerically larger in the high treated fish than the untreated controls, but sample size may have been too small to detect a significant difference. Some scoliosis was observed in the 5-6 day old samples of the high treatment. Selenomethionine appears to affect development of the vertebrae, but may not be affecting craniofacial development. We speculate that differences in craniofacial development between sturgeon and bony fishes (teleosts) may in part explain the lack of craniofacial effects selenomethionine of sturgeon.
