Physico-chemical characteristics of the improved extensive shrimp farming system in the Mekong Delta of Vietnam

Abstract

Consecutive failure of the improved extensive shrimp farming system has deterred the economy of some coastal areas in Vietnam. To investigate pond physicochemical characteristics, a monitoring scheme was performed in the Cai Nuoc district of Southern Vietnam. Results show that the system was not optimal for shrimps.While ponds were not contaminated by organic loadings or major nutrients (N, P) and salinity and pH were most optimal for shrimp, more than 37% of dissolved oxygen (DO) measurements were lower than recommended. In the early morning hours, DO measurements were even much lower (0.84^2.20 mg L À 1 ). Sulphate (SO 4 2 À ) concentrations were most within the acceptable range. Total suspended solids (TSS) were above the acceptable limit (o50 mg L À 1 ). Iron, alkalinity and hydrogen sulphide were also higher than recommended. Pond sediment was anaerobic (redox potential À 422 to À 105 mV) and contained high amounts of organic matter (9.842 1.96%). Lethal DO levels, high TSS and anoxic sediment are the drawbacks in this system. Suggested measures to improve pond conditions are (1) allowing sedimentation before ¢lling culture ponds, (2) covering dikes, (3) including no-culture breaks between shrimp crops, (4) drying pond bottom, (5) removing sediment and (6) controlling pond's vegetation.

Concurrent rice-shrimp-crab farming systems in the Mekong Delta: Are conditions (sub) optimal for crop production and survival?

“…The minimum individual harvest weight was 17 g in 2014 and 29 g in 2015. Under the P. monodon growth model of Jackson and Wang (1998), and given the mean monthly minimum water temperature of the ponds for 2014 (25°C) and 2015 (27°C), shrimp would take~120 days and 180 days to reach the minimum 2014 and 2015 harvest weights respectively (comparable with culture periods reported elsewhere; Tho et al, 2011). Mud crab (S. paramamosain, crablet stages 1 and 2) were also stocked periodically throughout the study period at densities of 0.4 ind./m 2 .…”

“…chronic) periods of sub‐lethal DO, as opposed to short‐term, acute events, are particularly stressful for shrimp (Allan & Maguire, ) but are not uncommon in rice‐shrimp farms in the region (e.g. Tho et al., ). Additionally, the combination of poor water quality conditions (beyond low DO alone), as measured in our study, likely exacerbates shrimp stress and ultimately poor production outcomes.…”

“…either above or below) the optimal range of values for shrimp, based on the ranges provided in the studies by Anon. (2006) and Tho et al (2011), and using the most conservative ranges where differences existed between these two sources, for water temperature, salinity, dissolved oxygen, alkalinity, pH, dissolved inorganic nitrogen (NO 2 -N, NO 3 -N, NH 4 -N) and TSS (Table 1). We performed the same calculation for water salinity based on the optimal range for rice production (<1.6 g/L, or <3.0 dS/m; Grattan, Zeng, Shannon & Robert, 2002).…”

“…Since the 1980s, farming systems have evolved to improve production, and today the black tiger prawn, Penaeus monodon , is the most commonly cultured shrimp in the dry season (Joffre & Bosma, ; Nhuong et al., ; Tho, Ut & Merckx, ). Farmers also stock other animal species on occasion (e.g.…”

Co-producing Better Management Practice standards for shrimp aquaculture in Indonesia

“…These are well established measures for more intensive forms of production aimed at mitigating the incidence of disease by reducing the incidence of virus carrying organisms, reducing excessive nutrient loads and reducing the acidity of pond soil -all of which are also major factors in reducing the overall productivity of ponds (e.g. Tho et al 2011;Walker and Mohan 2009). However, producers state that none of these measures are feasible in their extensive systems.…”