Effect of periphyton on growth performance of grey mullet, Mugil cephalus (Linn.), in inland saline groundwater ponds

摘要

The present study attempts to assess the potential of artificial substrates to enhance fish production in inland saline groundwater ponds through periphyton production. Grey mullet, Mugil cephalus, was cultured for 100 days in ponds with substrate (treatment ponds) and without substrate (control ponds). To enhance the surface area, bamboo poles were used as substrate. The periphyton population, pigment concentration and hydrobiological characteristics of pond water were monitored. The studies revealed little difference in most of the water quality parameters observed in the two treatments. However, turbidity (27.0+/-0.1-35.0+/-0.1 Nephalo Turbidity Unit (NTU)), chlorophyll 'a'(6.6+/-0.6-7.6+/-0.6 mug L-1), plankton population (phytoplankton 8.4x10(3)-9.4x10(3) numbers L-1; zooplankton 4.0x10(3)-5.1x10(3) numbers L-1) and NH4-N (2.0+/-0.2-2.3+/-0.1 mg L-1) were high in the treatment with no additional substrate; however, in the treatment with substrate the total Kjeldahl nitrogen (9.8+/-0.8-10.8+/-0.7 mg L-1) and o-PO4 (0.1+/-0.01-0.1 mg L-1) remained significantly (P<0.05) higher. Highest periphyton biomass in terms of dry matter (DM) (0.8+/-0.01-1.4+/-0.01 mg cm(-2)), ash free DM (0.4+/-0.0-0.6+/-0.01 mg cm(-2)), chlorophyll 'a' (3.1+/-0.2-8.1+/-0.8 mug cm(-2)) and pheophytin 'a' (1.9+/-0.4-3.9+/-0.5 mug cm(-2)) was observed at 50 cm depth in ponds provided with additional substrate. Fifteen plankton genera showing periphytic affinity colonized the bamboo substrates. Fish growth (mean fish weight 524.3+/-8.7 g and SGR 2.5+/-0.1) was significantly (P<0.05) higher in ponds provided with additional substrate compared with control ponds (387.2+/-6.0). Length-weight relationship (LWR) (W=cL(n)) also showed that the exponential value ('n') of length was high in substrate-supported ponds (n=2.36) in comparison with controls (n=1.09). These studies suggest that a periphyton-supported aquaculture system can be used successfully for the culture of herbivorous brackishwater fish species like M. cephalus in inland saline groundwaters and thus could contribute to the development of sound and sustainable aquaculture technology.