Diversification of brackishwater aquaculture in Indonesia: tilapia culture in Aceh

Traditional brackishwater aquaculture in Indonesia focuses on production of shrimp and milkfish. However, since the 1990’s production of shrimp, particularly Penaeus monodon, has become problematic because ofthe prevalence of white-spot disease. Crop losses due to white-spot disease have limited production of P. monodon in traditional tambak throughout Indonesia. Because of this, many tambak have fallen into disuse, or their use islimited. In response, we are developing and trialling diversification options for tambak farmers in Aceh and South Sulawesi. Alternative production options that we are evaluating include Nile tilapia (ikan nila) and soft-shell crab(kepiting lunak) in Aceh, and Nile tilapia, swimming crab (rajungan) and rabbitfish (baronang) in South Sulawesi. In Aceh our main focus has been on Nile tilapia (Oreochromis niloticus) culture, either alone or co-cultured with milkfish (Chanos chanos). We have undertaken trials with farmers in Samalanga and Jangka (Kab. Bireuen) and Banda Mulia (Kab. Aceh Tamiang). Overall, our trials have shown that tilapia will grow and survive well at salinities below 20 ppt. Above 20 ppt, growth rate is reduced and the fish are prone to bacterial disease. At salinities above 20 ppt, milkfish (bandeng) perform better in ponds than tilapia. Our trials in Aceh have demonstrated that Nile tilapia can provideincome to farmers comparable with shrimp culture. Out of a total of 22 trials to date, 9 ponds (41%) have met or exceeded our reference profitability of IDR 1–5 million per hectare per crop. Fourteen ponds (64%) have been‘profitable’, i.e. have generated positive economic returns. This figure is similar to the profitability figure for traditional shrimp ponds (64–73%), indicating that Nile tilapia culture in brackishwater ponds provides economic returns similar to traditional shrimp culture. Based on these results, we recommend Nile tilapia culture to farmers whose ponds are 20 ppt. This provides a profitable production option for farmers in areas subject to low salinities, or during the rainy season when salinities are depressed. Because outbreaks of white-spot disease are particularly common and severe during the rainy season, Nile tilapia culture provides a viable option for income generation for Acehnese tambak farmers under conditions where shrimp culture is too risk

Prevalence of Infectious Spleen and Kidney Necrosis Virus (ISKNV), Nervous Necrosis Virus (NNV) and Ectoparasites in Juvenile Epinephelus spp. Farmed in Aceh, Indonesia

A cross-sectional survey was used to estimate the prevalence of infections with the Infectious spleen and kidney necrosis virus (ISKNV, Megalocytivirus), nervous necrosis virus (NNV, Betanodavirus), and infestations with ectoparasites during the rainy season in juvenile grouper (Epinephelus spp.) farmed in Aceh, Indonesia. The survey was intended to detect aquatic pathogens present at 10% prevalence with 95% confidence, assuming 100% sensitivity and specificity using a sample size of 30 for each diagnostic test. Eight populations of grouper from seven farms were sampled. Additional targeted sampling was conducted for populations experiencing high mortality. Infection with NNV was detected at all farms with seven of the eight populations being positive. The apparent prevalence for NNV ranged from 0% (95% CI: 0–12) to 73% (95% CI: 54–88). All of the fish tested from the targeted samples (Populations 9 and 10) were positive for NNV and all had vacuolation of the brain and retina consistent with viral nervous necrosis (VNN). Coinfections with ISKNV were detected in five populations, with the highest apparent prevalence being 13% (95% CI: 4–31%). Trichodina sp., Cryptocaryon irritans and Gyrodactylus sp. were detected at three farms, with 66% to 100% of fish being infested. Hybrid grouper sourced from a hatchery were 5.4 and 24.9 times more likely to have a NNV infection and a higher parasite load compared to orange-spotted grouper collected from the wild (p < 0.001). This study found that VNN remains a high-impact disease in grouper nurseries in Aceh, Indonesia