Abstract

Freshwater mussels (family Unionidae) are critically imperiled with an estimated 70% of species classified as endangered, threatened or of special concern.⁴ Many mussel species are declining so rapidly that their existence may come to depend on captive management and propagation. Unfortunately, when relocated or brought into captivity, a high proportion of these normally long-lived animals die within the first year.² The development of nonlethal methods of hemolymph collection from mussels³ has facilitated progress in identifying cytological¹ and chemical³ indicators of health, once reference ranges are established. The logistics of a full year of data collection in the wild is challenging, limiting data collection to summer only. Use of a captive flow-through system that attenuates dynamic, environmental fluctuations may be a way to develop reliable reference ranges for freshwater mussels that are more inclusive of its year round physiology. This study aimed to 1) provide initial reference ranges for cellular differentials and chemistry values from two common genera, Amblema plicata (n = 21) and Quadrula spp. (n = 18), collected and sampled in the wild; and 2) develop an understanding of shifts in cellular differentials and chemical fluctuations in each genera by translocating A. plicata (n = 16), Quadrula spp. (n = 14) animals into a captive flow through facility and monitoring the population over one year. Nine of the original 40 animals sampled in the wild were translocated into captivity as captive controls.

Cellular differentials included four cell types: eosinophilic granulocyte, basophilic granulocyte, large agranulocyte and small agranulocyte enumerated at each time point. Chemical constituents measured in hemolymph included: sodium, chloride, potassium, phosphorus, magnesium, calcium, glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP). Eosinophilic granulocytes predominated in both genera. In A. plicata, eosinophilic granulocytes ranged from 53 to 73%, large agranulocytes from 19 to 41%, basophilic granulocytes from 1 to 6% and small agranulocytes from 1 to 3%, compared to Quadrula spp. with 44–61% eosinophilic granulocytes, 8–27% basophilic granulocytes, 28–40% large agranulocytes, and less than 1 % small agranulocytes. Cell differentials were found to be genus-specific at baseline and for the first month in captivity (p < 0.05). Total hemocyte counts between genera differed at 2 weeks and in November (p < 0.10). Significant differences in sodium, potassium, chloride, magnesium, ALT, AST, and ALP were found between genera at baseline (p < 0.05). Both genera showed declines in sodium, chloride, and potassium in the first month in captivity and had marked increases in all electrolyte values in November. Calcium and glucose values remained steady in the population until the last collection point in June when values in both parameters declined. Phosphorus levels increased in both genera with significantly higher levels seen in A. plicata in February (p < 0.05). A greater proportion of animal deaths occurred after winter sampling, potentially indicating that sampling during winter quiescence is not recommended. This study provides a foundation for hematological and chemical baseline reference ranges for A. plicata and Quadrula spp. and a preliminary understanding of shifts in blood cells and hemolymph chemistries in a population of mussels in captivity over one year.

Acknowledgements

I would like to thank Trisha Gibson, Brooke Kelly, Kody Kuehnl, and Tom Watters from the Columbus Zoo and Aquarium Freshwater Mussel Conservation Research Center for their mussel expertise and dedication to the conservation of these imperiled amazing little creatures. Many thanks to the Morris Animal foundation, the Ohio Division of Wildlife, the Columbus Foundation and Chemical Abstracts for support of this research.

References

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3.  Volety AK. 2008. Effects of salinity, heavy metals and pesticides on health and physiology of oysters in the Caloosahatchee Estuary, Florida. Ecotoxicology 2008; 17(7): 579–590.

4.  Burkard MJ, Leavell SA, Weiss RB, Kuehnl K, Valentine KH, Watters GT, Wolfe BA. Analysis and cytologic characterization of hemocytes from freshwater mussels (Quadrula spp). Vet Clin Pathol 2009; 38(4): 426–436.