Effects of High Stocking Density on Condition Factor and Profile of Free Thyroxine and Cortisol in Catla catla (Hamilton, 1822) and Labeo rohita (Hamilton, 1822)

Özet

High stocking density is a major problem in extensive aquaculture in Pakistan. Present study investigated its effect ofgrowth, levels of thyroxine (T4) and cortisol in two major carps of Pakistan; labeo (Labeo rohita) and catla (Catla catla). Onecohort of labeo (n=30) was kept at high stocking density (HD) (25 g/L). HD cohort was split into two replicates, eachcontaining a total of 15 fish. Second cohort of labeo (n=10) was reared at low stocking density (LD) of 4.4 g/L. LD cohortwas divided into two replicates, each containing a total of five fish. Similar protocol was followed for catla. Trial continuedfor the period of 30 days. At the end of trial, condition factor significantly decreased in HD cohorts of both species. Levels ofcortisol in HD cohorts (210±2.00 nmol/L in Catla catla; 425±3.00 nmol/L in Labeo rohita) were significantly higher thanthose in LD cohorts of both species. Values of T4 in HD cohorts were found to be 1.48±0.20 pmol/L in Catla catla and1.74±0.10 pmol/L in Labeo rohita at the end of trial which were significantly lower than at the commencement of trial.Suppression of growth, elevation in the levels of cortisol and decrease in profile of T4 in HD cohorts of both species was dueto stress induced by high stocking density. Furthermore, present study found that optimum stocking density for extensivefarming of both species should be approximately 4.4 g/L.