Stress responses in rohu, Labeo rohita transported at different densities

• The changes in biochemical and haematological indices in rohu, Labeo rohita have been investigated to optimize the packing density.
• The levels of serum ALT, AST, LDH, creatinine, cortisol and glucose production were significantly increased.
• The serum ALT levels increment was more prominent.
• The optimum packing density for advanced rohu fingerlings for 2–3 h duration of transport would be 134 g L−1 of water.

Transportation of fish, although stressful, is an inevitable procedure in aquaculture practices. In this study, we investigated the changes in biochemical and haematological indices in advanced fingerlings of rohu, Labeo rohita in order to optimize the packing density as is imperative to avoid transportation stress and associated mortality. The fish (14.00–15.00 cm) were packed in sealed double layer oxygen packed polythene bags of 30 L capacity containing 7.5 L of water and transported for 2 h and 30 min in a motor vehicle at three packing densities, viz., 67 g L−1, 134 g L−1, and 201 g L−1 and transported from hatchery to Kolkata, India covering a distance of about 55 km. A cumulative mortality of 30% was recorded during and after transportation in fish transported at 201 g L−1; while the other two packing densities recorded no mortalities. Transportation and packing density induced stress affected the functioning of liver and kidney. The activities of transaminases and lactate dehydrogenase, breakdown of protein and creatinine phosphate, cortisol induced glucose production were significantly increased in advanced rohu fingerlings to cope with the energy demand posed by transportation and higher packing density stress. Low levels of dissolved oxygen and high levels of ammonia-nitrogen were noticed in different packing densities after transportation. The results suggested that the optimum packing density for advanced rohu fingerlings for 2–3 h duration of transport would be 134 g L−1, which kept the stress at low levels. The serum alanine aminotransferase levels can serve as a good marker for fish liver health as the increment was more prominent when subjected to transportation stress.