Plasma Stress Responses in Juvenile Red-Spotted Grouper (Epinephelus akaara) exposed to Abrupt Salinity Decrease.

Area of Science:

• Aquaculture
• Fish Physiology
• Environmental Stress

Background:

• Epinephelus akaara (red grouper) is an important aquaculture species.
• Understanding salinity tolerance is crucial for optimizing aquaculture practices and predicting environmental impacts.

Purpose of the Study:

• To investigate the acute plasma stress responses of juvenile Epinephelus akaara to abrupt decreases in salinity.
• To determine the no observed adverse effect level (NOAEL) for acute salinity challenges in this species.

Main Methods:

• Two size groups of juvenile E. akaara were exposed to varying salinity drops (34 PSU to 26, 18, or 10 PSU) for 72 hours.
• Plasma parameters (glucose, GOT, GPT, RBC count) and gill histology were analyzed.
• Fish physiological responses were monitored over the 72-hour exposure period.

Main Results:

• Significant increases in plasma glucose, glutamic oxalate transaminase (GOT), and red blood cell (RBC) counts were observed at 18 PSU and 10 PSU.
• Gill histological alterations, including hyperplasia and epithelial lifting, were noted at 18 PSU and 10 PSU.
• Fish exposed to 26 PSU showed osmotic adjustments, while those at 18 PSU and 10 PSU were in the primary adjustment phase.

Conclusions:

• The no observed adverse effect level (NOAEL) for a 72-hour acute salinity challenge in juvenile E. akaara was determined to be 26 PSU.
• Salinity drops to 18 PSU and below can induce acute adverse effects, potentially making fish more susceptible to additional stressors like temperature changes or handling.
• These findings are critical for managing E. akaara aquaculture and mitigating risks associated with environmental salinity fluctuations.