RESPIRATORY ADAPTATIONS OF THE ESTUARINE MUD SHRIMP, CALLIANASSA JAMAICENSE (SCHMITT, 1935) (CRUSTACEA, DECAPODA, THALASSINIDEA)

¹ Department of Biology, University of Southwestern Louisiana, Lafayette, Louisiana 70504

Callianassa jamaicense survives exposure to aquatic and aerial anoxia for more than 3 days. In normoxic water-saturated air it survives for ca. 16 days. The rate of oxygen consumption (V_o2) in air is less than 40% of V_o2 in water. Aquatic V_o2 is regulated above critical oxygen tensions (P_c) of 10 to 25 mmHg when animals are allowed to slowly deplete oxygen from a sealed bottle. Mean aquatic V_o2 of animals in a flow-through respirometer or in tubes placed into sealed BOD bottles ranges from 50 to 68 µl/ (g wet wt·hr) over oxygen tensions (P_o2) above the P_c.

After a 12-hr exposure to anoxic water, V_o2 is not regulated; post-anoxia V_o2 in hypoxic water (37 mmHg) is initially less than V_o2 measured in normoxic water (150 mmHg) before exposure to anoxia; post-anoxia V_o2 in normoxic water is initially two times the pre-anoxia V_o2 and suggests the development of an oxygen debt during anoxia. When P_o2 of ambient water is abruptly dropped from 150 to 37 mmHg, specimens of C. jamaicense exhibit a partial shutdown of aerobic metabolism, but the V_o2 begins to recover after 6 hr in hypoxia.

When oxygen tension is slowly decreased, pleopod ventilation rate varies little as P_o2 changes from 120 to 20 mmHg. The pleopod ventilation rate increases as P_o2 falls 20 to 10 mmHg, but decreases below 10 mmHg and stops after several hours under anoxia. The rapid response of taxis and pleopod activity when C. jamaicense is exposed to altered P_o2 suggests rapid perception of external oxygen levels and provides further circumstantial evidence of an oxygen receptor in thalassinids.

Tolerance of anoxia, metabolic regulation to a low P_c, low metabolic rates, metabolic responses following anoxia, and taxic response to altered P_o2 constitute adaptations to the hypoxic habitat of C. jamaicense.