Aquaculture and the environment: the supply of and demand for environmental goods and services by Asian aquaculture and the implications for sustainability

The present paper explores the relationships between aquaculture and the environment In Asia, focusing on the demands for environmental goods and services among different sectors. Aquaculture in the region accounts for 88% of global production by weight and 80% by value. Nevertheless, environmental problems are increasingly apparent and the higher the demands for environmental goods and services, the more negative the impacts. Against a background of rapid social, economic and political change, the paper considers how the sustainability of the industry is best assured. An integrated view of resource use, in which aquaculture is but one activity, is necessary for sustainable development. The roles of planning, education, research and environmental management schemes are discussed.     

Biological Observations on the Mudskipper Pseudapocryptes elongatus in the Mekong Delta,Vietnam

Aspects of the population biology of the mudskipper, Pseudapocryptes elongatus, (Cuvier, 1816) were studied in Bac Lieu Province in the Lower Mekong Delta, Vietnam, including sex ratio, length–frequency distribution, sexual dimorphism, hepatosomatic index (HSI), female gonadosomatic index (GSI), gonad histology, fecundity and some observations on post‐larvae and juveniles. In the population studied the sex ratio was skewed toward males. Females had a shorter mean length and a lower mean growth rate than males. No mature males or females were observed among mudskippers sampled in estuarine canals from February to May 2004 during the dry season. It is suggested that P. elongatus migrates to the sea to spawn later in the year after onset of the wet season. Salinity tolerance was evaluated in a 96‐h experiment. This showed that P. elongatus is remarkably euryhaline and able to survive in salinities ranging from freshwater to 50 ppt. Gut content analysis revealed that P. elongatus is a herbivore, feeding mainly on pennate diatoms (93% of the diet).     

The influence of stocking density and food ration on fry survival and growth in Oreochromis mossambicus and O. niloticus female × O. aureus male hybrids reared in a closed circulated system

First-feeding stage tilapia fry were reared for 40 or 50 days in 20-l capacity aquaria at six stocking densities (2, 4, 6, 8, 10, 12 l^?1) and three feeding levels (6, 12, 24% of body weight daily). Fry survival and growth were improved at the higher feeding levels, but the percentage of fry surviving showed no consistent relationship to stocking density. Cannibalism accounted for a mortality rate of 10–35% in each experimental group and was inversely related to the level of feeding. Under equivalent conditions, O. niloticus female × O. aureus male fry had a higher rate of survival, better food conversion and were more uniform in size than O. mossambicus fry.     

Student Opportunity: Short-Term Exposure to International Agriculture

Opportunities abound to apply crop science to solving many of the world’s food problems. International agricultural research centers (IARCs) provide a window through which students can see the need for improved agricultural productivity and briefly experience the rewards of working on difficult but important issues. In today’s world of highly technical graduate education, students find it difficult to obtain exposure to international agriculture due to the extreme constraints on their time. Programs for students that provide a short-term exposure to IARC strategies can have long-term benefits for the student as well as the international center. A short-term student exchange program between a US university and the International Rice Research Institute (IRRI) and a special course on rice (research to production) offered at IRRI provide students with unique insights for averting food riots in the future. Details of these educational efforts are described in this paper.     

Pond production of the mud crabs Scylla paramamosain (Estampador) and S. olivacea (Herbst) in the Mekong Delta, Vietnam, using two different supplementary diets

The production performance of Scylla paramamosain and S. olivacea reared together in ponds and provided with different supplementary diets (crustaceans or trash fish) were evaluated with that of an unfed control group relying only on natural food available within the pond. Each treatment was conducted in triplicate. The aim was to evaluate two production strategies over a 130‐day grow‐out trial: (1) production to 200 g crab^?1, which is the minimum preferred marketable size in the Lower Mekong Delta (LMD) and (2) production to 300 g crab^?1, the size that fetches the highest market price. Growth production models were estimated which revealed that the rearing period required to produce crabs of 200 g was 102 days with supplementary feeding, compared with 120 days for the unfed control group. The rearing period needed to produce 300‐g‐sized crabs was estimated to be 144 days and 186 days for the supplementary fed and unfed groups respectively. The additional risk involved in rearing mud crabs to 300 g is not considered worthwhile, under similar culture conditions as observed in this trial, as a decrease in pond water quality and higher mortality rates were observed in the final month of culture needed to achieve this larger size.     

Morphometry and abnormalities of the feet of Kaimanawa feral horses in New Zealand

Objective The present study investigated the foot health of the Kaimanawa feral horse population and tested the hypotheses that horses would have a large range of foot morphology and that the incidence of foot abnormality would be significantly high. Procedures Abnormality was defined as a variation from what the two veterinarian assessors considered as optimal morphology and which was considered to impact negatively on the structure and/or function of the foot. Fifteen morphometric variables were measured on four calibrated photographic views of all four feet of 20 adult Kaimanawa feral horses. Four morphometric variables were measured from the lateromedial radiographs of the left forefoot of each horse. In addition, the study identified the incidence of gross abnormality observed on the photographs and radiographs of all 80 feet. Results There was a large variation between horses in the morphometric dimensions, indicating an inconsistent foot type. Mean hoof variables were outside the normal range recommended by veterinarians and hoof care providers; 35% of all feet had a long toe conformation and 15% had a mediolateral imbalance. Abnormalities included lateral (85% of horses) and dorsal (90% of horses) wall flares, presence of laminar rings (80% of horses) and bull-nose tip of the distal phalanx (75% of horses). Both hypotheses were therefore accepted. Conclusions The Kaimanawa feral horse population demonstrated a broad range of foot abnormalities and we propose that one reason for the questionable foot health and conformation is lack of abrasive wearing by the environment. In comparison with other feral horse populations in Australia and America there may be less pressure on the natural selection of the foot of the Kaimanawa horses by the forgiving environment of the Kaimanawa Ranges. Contrary to popular belief, the feral horse foot type should not be used as an ideal model for the domestic horse foot.