Abstract: A study of time series behavioural effects and post mortem changes of Clarias gariepinus under varying gear handling conditions was carried out using forty live samples of Clarias gariepinus of average body weight 165 gm bought from Aleshinloye market in Ibadan, Oyo State, Nigeria. The samples were grouped into 4 treatments A, B, C and D with 10 pieces in each treatment. Treatment A fish were fixed to Hook and line, fish species in treatment B were fixed to the gill net, treatment C fish were dragged from the pond with a dragnet and fish in treatment D (which served as the control) were washed with clean water and left to die naturally in a clean bowl of water. All treatments were left in the different gears to struggle and die at ambient temperature. They were also left in their various conditions after death for rigor mortis to occur and the time taken for rigor to resolve was noted and at the temperature they occurred. After fish from each treatment were packed in polythene bags with labels and then stored in the freezer at a temperature of-20°C. Organoleptic and chemical assessment test were carried out on samples of each treatment every fortnight for 10 weeks. The death time/rigor time and temperatures at which they occur were as follows:-Treatment A (Hook and line) 158.5 mm death time/181.00 rigor time at 26°C. Treatment B gilled fish) death time 241.50 min/169.00 min rigor time at 28°C. Treatment C (Dragged fish) death time 667.00 min/269.50 min. rigor time at 25°C. Treatment D (control left to die naturally) death time was 827.00 min/289.50 min. rigor time at 26.50°C. Rigor mortis does not last longer in struggling and exhausted fish as it is the case with treatments B and A coupled with their earlier death than in treatments C and D, although rigor mortis started earlier in C. Hence treatment A and B showed earlier signs of spoilage than C and D. Significant differences exist p<0.05 between the Total Volatile Base (TVB) and the weeks of storage with the gilled fish (Treatment B) having the highest overall TVB accumulation of 93.00 mg 100 gm^-1 fish indicating the fastest rate of spoilage, followed by Hook and line (Treatment A) 88.20 mg 100 gm^-1 fish, ranking third is the Dragged fish (Treatment C) with 84.50 mg^-1 100 gm fish, while the least value of 79.20 mg^-1 100 gm fish was recorded (in the control) indicating least spoilage. The organoleptic assessment followed a similar pattern. This is further confirmed by the positive correlation coefficients (A-r = 0.99, B-r = 0.99, C-r = 0.60 and D-r = 0.98) in all cases indicating increase rate of spoilage with storage length (weeks). The best gear to use for catching Clarias gariepinus (apart from allowing the fish to die naturally) as shown in the study is the DRAGNET, since this exerted far much less stress on the fish.