This article presents technical and bioeconomic information on culture-based grow-out production of groupers in Vietnam.Grouper farming has good future potential as a viable alternative livelihood for fishers. It is found to be very profitable for cage farmers in northern Vietnam and marginally profitable for cage and pond farmers in central Vietnam. Productivity and total revenue are highest in the north, reflecting relatively high stocking rates, aquaculture area, and harvest prices. Cost per unit production is highest for centrally located cage farmers. The dominant cost sources for these farms are feed (40-60% of total costs) and, to a lesser extent, seed (20%) and labor (12-19%). The feed conversion ratios for these systems, where grouper are fed exclusively low-value finfish, is calculated to be 9 in the north and 12 in the center. It seems that improving the livelihood of grouper farmers in Vietnam is dependent on reducing their dependence on wild stocks for seed and feed, and increasing area and growout time for central farmers. If pellets are to be widely adopted by grouper farmers, perceptions regarding the poor adaptability, relatively slow growth rates compared with low-value finfish, and poor availability of pellets need to be overcome.

The results of bioeconomic analysis informed by a survey of 80 small‐scale mud crab farmers in Vietnam are presented in this paper. Mud crab farming in Vietnam is profitable, with net revenue being approximately 135 and 41 million VND/year (USD 7000–USD 2100 per year) in the central and southern regions, respectively. Profitability was significantly higher in the centre compared with the north, as almost three times the biomass is harvested in the centre compared with the south (in turn, due to higher aquaculture area and survival rates). The benefit–cost ratio (the ratio between total revenue and total costs) is 3.55 in the centre and 1.97 in the south. The crabs are fed almost exclusively on low‐value finfish in the centre and the south. Feeding rates were found to be low, with 95% of biomass gain coming from natural feed in the environment rather than supplementary feeding by the farmer. If pellets are to be adopted widely by mud crab farmers, negative perceptions regarding the poor adaptability of mud crab to pellets (northern farmers only), relatively slow growth rates compared with low‐value finfish and lack of availability of pellets need to be overcome.

Culture‐based growout of tropical spiny lobster, Panulirus ornatus, is a nascent and unique industry that faces a number of challenges and opportunities. Of particular interest to this study is the imminent development of pelleted diets for lobster (probably within 3 yr) that will potentially reduce the industry's dependence on bycatch for feed (with benefits to wild stocks of fish and reduced downstream environmental impacts). The aim of this paper is to conduct a bioeconomic analysis of lobster growout farming in Vietnam and analyze the cost‐effectiveness of potential manufactured feed diets for these farms. Growout lobster farming is found to be a high‐cost and high‐return industry, with a benefit cost ratio of approximately 1.44. Approximately 60% of the total costs are feed related, with the quantity of feed being the production parameter with the highest variability. Hence, reducing the cost and increasing the efficiency of feeding will have a significant impact on the level and variability of profit. It is expected that manufactured diets will improve the profitability by approximately 267 million VND/yr for an individual farmer (15,000 USD) and approximately 435 billion VND/yr for the industry (24 million USD). This is expected to double again if the diets have the added benefit of reducing mortality through the inclusion of vitamins and other additives.

Selective breeding for marine finfish is challenging due to difficulties in reproduction, larval rearing, and on-growth in captive environments. The farming of Asian seabass (Lates calcarifer) has all these problems and our knowledge of the quantitative genetic information (heritability and correlations) of traits necessary for commercial exploitation is poor. The present study was conducted to address this knowledge gap and to provide information that can be applied to sea bass and other aquaculture species. We carried out a comprehensive genetic evaluation for three traits (body weight, total length, and survival) collected from a breeding population for Asian seabass over an eight-year period from 2010 to 2017. Statistical analysis was carried out on 4,567 adult fish at 105, 180, 270, 360, 450, and 570 days post-hatch (dph). The heritabilities (h2) estimated for body weight and length using linear mixed model were moderate to high (0.12 to 0.78 and 0.41 to 0.85, respectively) and they differed between the measurement periods. Survival during grow-out phase was analyzed using threshold logistic and probit models. The heritability estimates for survival rate on the underlying liability scale (hL2) varied from 0.05 to 0.21. When the observed heritability obtained from the linear mixed model was back-transformed to the liability scale, they were similar but not significant. In addition, we examined effects of genotype by environment (G × E) interaction on body traits. The genetic correlation for body weight between tank and sea cage cultures were high (0.91–0.94) in the first and second rearing periods (180 and 270 dph) but the correlation was decreased to 0.59 ± 0.33 at 360 dph. This suggests that the genotype by environment interaction is important for body traits in this population. Furthermore, the genetic correlations of body weights between different measurement periods were moderate but different from one. This suggests that body weights measured at different time points may be different traits and selection for improved early weight may not capture all genetic expressions in subsequent rearing periods in Asian seabass. Selection of the nucleus in sea cages may produce genotypes that do not perform equally well in tanks, although this deserves further studies to determine a suitable selection environment and optimize the breeding program. This paper discusses challenges encountered during implementation of the selection program for L. calcarifer.

This study assessed the protein and energy requirements of Cobia (Rachycentron canadum) using a bio-energetic factorial approach. Using a series of interrelated studies, several parameters were defined to enable the construction of a bio-energetic factorial model for this species. The studies included two controlled laboratory experiments and also extensive field-data collection from commercial and research farms in Vietnam. The devised model includes parameters for both maintenance and protein demands; the effect of fish live-weight on maintenance protein (LW 0.697), lipid (LW 0.972), and energy demands (LW 0.815); the efficiencies of protein, lipid and energy utilisation at various protein, lipid and energy intake levels; and the variability in whole body composition with varying live-weight. The protein utilisation efficiencies (0.456 • [protein intake]-0.445), lipid utilisation efficiencies (1.292 • [lipid intake]-1.120) and energy utilisation efficiencies (0.651 • [energy intake]-48.41) were similar to other carnivorous fish species. However, the maintenance requirements for both energy (74.3 kJ/ kgBW 0.8 / dat 28ºC) and protein (0.99 g/ kgBW 0.7 /d at 27.9ºC) were about double to other species. Using this modelling approach it was possible to iteratively derive optimal dietary protein and energy specifications for this species.