Evaluation of productions and economic returns from two brackishwater polyculture systems in tide-fed ponds.

摘要

To compare the production and economic performance of two polyculture systems with different species combinations in brackishwater tide-fed ponds, a 180-day trial was carried out. In the first combination (T1), mullets (Mugil cephalus, Liza tade and L. parsia at 3:1:1.3 ratio) and tiger shrimp (Penaeus monodon) and in the second (T2), milkfish (Chanos chanos) and tiger shrimp were stocked keeping the fishes and shrimp at 8000 and 20 000 numbers ha-1, respectively, in both treatments with duplicate ponds. Since shrimp was an important component of these two systems with open water exchange, the dynamics of heterotrophic bacteria (THB) including Vibrio spp. (TVC) and the occurrence of viral infection agents were studied to understand the disease risks. Among the fishes in T1, M. cephalus attained the highest final weight of 92.29+or-4.36 g followed by L. tade and L. parsia with 80.40+or-4.02 and 54.02+or-2.11 g, respectively. C. chanos in T2 had the highest net weight gain (127.85 g) and daily weight gain (0.71 g day-1), while M. cephalus in T1 attained the highest specific growth rate (1.60% day-1). Growth parameters of tiger shrimp were almost similar in both treatments, with no significant differences (P>0.05). Though total production of fishes and shrimp was lower in T1 (689 kg ha-1 180 day-1), it was not significantly different (P>0.05) from T2 (721 kg ha-1 180 day-1). Monthly THB and TVC were not alarming and the absence of viral infections in shrimp indicated no disease risk. Total income from T1 was significantly higher (P<0.05) than that of T2, but net income and benefit-cost ratio were insignificantly different between the treatments (P>0.05). The present findings indicate that upon availability of stocking materials, both polyculture systems would be suitable farming options.