Abstract
Nile tilapia Oreochromis niloticus, a euryhaline species, is a good candidate for culture in estuarine areas in the Philippine archipelago. Thus, the effects of stocking density on plasma cortisol, blood glucose, plasma aspartate transaminase (AST), and plasma alanine transaminase (ALT) were determined. The group of juvenile Nile tilapia O. niloticus (14.67 ± 0.12 cm TL and 44.57 ± 0.48 g W) was subjected to three different stocking densities (6, 12 & 24/60 L) for 14 days in 15‰ rearing condition. The experiment was composed of three treatments with triplicated groups arranged in a completely randomized design (CRD). Highest stocking density affected the plasma cortisol, blood glucose, plasma AST and ALT of Nile tilapia by increasing its concentration level in the blood. These manifestations suggest that overcrowding in Nile tilapia affects the physiological function through hormonal secretion, glucose utilization, and protein catabolism of the species.
Highlights
Nile tilapia Oreochromis niloticus L. is a euryhaline species that has considerable potential for culture in high saline waters, especially in the Philippines where estuarine environments are common
It commences with an initial short-latency increase in plasma levels of catecholamines released from stores in the chromaffin tissue of the kidney, followed by a longer latency but usually more prolonged elevation in plasma cortisol levels following de novo synthesis by interrenal tissue [7]
Blood glucose was quantified following the method of Mustafa et al, [12] in which ooze of fresh blood from the severed caudal peduncle was slightly dropped into the tip of the glucose strip that was inserted in a standard glucometer (Apex Biotechnology Corp.) and reading of the result was obtained in situ
Summary
Nile tilapia Oreochromis niloticus L. is a euryhaline species that has considerable potential for culture in high saline waters, especially in the Philippines where estuarine environments are common. With the invasion of tilapia production into the brackishwater, an appropriate stocking density in these farming areas should be put into consideration. Stress in fish affects its overall performance as it undergoes several responses that compromise health and growth. It commences with an initial short-latency increase in plasma levels of catecholamines released from stores in the chromaffin tissue of the kidney, followed by a longer latency but usually more prolonged elevation in plasma cortisol levels following de novo synthesis by interrenal tissue [7]. This study was conducted to determine appropriate stocking density in hyperosmotic conditions without compromising the overall health capability of the species. The hematological indices such as plasma cortisol, blood glucose, plasma aspartate transaminase, and alanine transaminase of juvenile Nile tilapia reared in hyperosmotic conditions were quantified
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