Effects of light intensity and photoperiod on the growth performance of juvenile Murray cods(Maccullochella peelii)in recirculating aquaculture system(RAS)

Murray cod(Maccullochella peelii)is a freshwater percichthyid fish that has a high market value and potential for culture in recirculating aquaculture systems(RASs).Illumination is an important environmental factor that affects the growth and physiological condition of fishes.A comprehensive understanding of the relationship between the light factors and the growth,nutrient composition and stress response of juvenile Murray cod in RAS is important to achieve satisfactory theoretical and practical aquaculture performance.Juvenile Murray cod were randomly assigned to nine RAS tanks with a volume of 1.5 m^(3),with each tank containing 120 fishes(3.5±0.5g).The fish were cultured for 120 days under different light intensities(1200,2400,and 3600 lx)and photoperiods(12L:12D,18L:6D and 24L:0D).The results showed that the final weight and feed conversion ratio of Murray cod under a light intensity of 1200 lx were significantly better than those under 3600 lx(P<0.05).The serum total protein and globulin were higher at the light intensity of 1200lx,compared to other light intensities.The blood urea nitrogen level improved with increasing light intensity at LD12:12 and LD18:6 of photoperiod,as well as the superoxide dismutase level improved significantly from LD18:6 to LD24:0 of photoperiod.The findings indicated that the optimal light condition to enhance growth at juvenile stage is 1200 lx of the light intensity and LD18:6 of the photoperiod.

A comparison of buffering species and regimes applied within a research-scale, recirculating aquaponics system

Murray Cod,Maccullochella peelii peelii,and Green Oak lettuce,Lactuca sativa,were used to test for differences between four buffering regimes in a research-scale,recirculating aquaponic system consisting of twelve,separate 140L aquaponic units.In the aquaponic system,where plant nutrients were supplied from fish wastes and plants stripped nutrients from the water before it was returned to the fish,the buffers tested were potassium bicarbonate,calcium hydroxide,mixed(an equal mixture of potassium bicarbonate and calcium hydroxide)and a control where the buffer used was sodium bicarbonate.Murray Cod had FCRs and biomass gains that were statistically identical in all treatments(SGR=1.19%/replicate/day;FCR=0.86).Lettuce yields were determined over a 21-day trial,with the potassium treatment(yield of 4.75 kg/m2)and mixed treatment(yield of 5.00 kg/m2)providing the highest production.Potassium and mixed treatments also had lower levels of nitrate accumulation(potassium treatment=7.80 mg/L;mixed treatment=8.77 mg/L)and the lowest levels of water use(potassium treatment=1.59 L/day;mixed treatment=1.60 L/day)compared with the other test treatment and the control.Mixed and calcium treatments yielded the lowest phosphate accumulations(mixed treatment=2.81 mg/L;calcium treatment=2.60 mg/L),but the calcium treatment may have been affected by calcium-phosphate complexing which may have led to false identifiable phosphate concentrations.For dissolved oxygen,pH and conductivity,no statistical differences were observed.Overall,results suggest that potassium-based buffer salts were superior to the other buffers tested in the research-scale aquaponic system tested.