3) Nitrogen and anaerobic metabolism and haemocyanin levels in the white shrimp Litopenaeus vannamei exposed to short term hypoxia.

In summer, high temperatures are combined with severe nocturnal hypoxia in shrimp farming ponds in Northwest Mexico. Under these conditions the white shrimp Litopenaeus vannamei, have shown some mortality when the duration of hypoxia times are longer than 3-4 h. Haemolymph ammonia, total protein, haemocyanin, lactate levels, and ammonia fluxes were measured in the white shrimp Litopeneaus vannamei challenged to short-term severe hypoxia (10 % oxygen saturation) for 30, 60, 90, 120 or 180 min at 28 ºC. The principal objective was to evaluate changes in the physiology of this species when being exposed to hypoxia over similar times to those that might encounter during its aquiculture farming in Northwest Mexico.

The data obtained here indicate that the mean ammonia efflux rate of this species under control conditions (normoxia) and 28 ºC was 8.00 ± 0.88 µmol g -1 h -1 this value being reduced to 3.81 ± 0.19 µmol g -1 h -1 after 180 min exposure to hypoxia. Mean normoxic blood haemocyanin levels were 1.04 ± 0.11 mmol L -1 with the lowest and highest value of 0.82 ± 0.06 mmol L -1 and 1.42 ± 0.08 mmol L -1 being measured after 180 m and 120 m of hypoxia, respectively. Haemolymph lactate level during normoxic conditions was 3.44 mg/dL this increasing to 45.39 mg/dL after 180 minute exposure to hypoxia. Large variability in data within individual time periods was found. Mortalities for the various time periods of hypoxia are: 0% (normoxia), 0% (30 minutes), 13% (60 minutes, 90 minutes, and 120 minutes) and 26% (180 minutes), respectively. The results are discussed in relation to the physiological ecology of the unique aquaculture farming conditions of L. vannamei in Northwest Mexico.