Stable carbon (d 13 C) and nitrogen (d 15 N) isotope ratios were measured to investigate the migration of John's snapper Lutjanus johnii and its dependence on the food resources provided within the large Matang Mangrove Forest Reserve (40,151 ha), Malaysia. John's snapper, and its main prey food such as penaeids, Acetes shrimps and mysids, showed generally depleted d 13 C values in the inner mangrove area but more enriched values in the river mouth and coastal area. Some juveniles migrated into the inner mangrove areas, although they were also distributed near the river mouth areas. Isotopic signatures of snapper fish and prey reveal the ontogenetic migration of the youngest juvenile fish (\5 cm in total length) from the coastal area into the mangrove area, shifting their dependence from the coastal food web to the inner mangrove food web with their growth. The study shows the importance of the complex interconnected mangrove waterways and associated prey animals present in the large mangrove system to juvenile John's snapper.

A mass mortality event of blood cockles, Anadara granosa, occurred in aquaculture ground in Selangor in mid-February 2012. To identify factors contributing to this event, we estimated the changes in survival rate and population density of the blood cockles using data from field surveys carried out in late-January and mid-March, 2012. In addition, blood cockle samples were used for histological observation of various tissues with a light microscope. Furthermore, we examined the environmental factors that seemed to be involved in this mass mortality event using environmental data obtained in two surveys and weather data for the Selangor region from late-January to mid-March 2012. As a result of the field surveys and the histological observation, the mortality was estimated to be 30 % over, and the blood cockles were shown to be in the spawning season at this time of year. In addition, numerous individuals collected in mid-March had no food in the digestive duct, which suggested low food availability. Precipitation data for the Selangor region showed rainfall of 30 mm/day over four days in mid-February, which suggested an impact of freshwater flooding from rivers on the aquaculture ground. Normally, the blood cockles are tolerant to low-salinity environments. However, the fact that the flooding and associated environmental changes occurred, when the population was debilitated by reproductive activity, may have led to the mass mortality event in association with low food availability.

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Stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) were determined for the spotted scat (Scatophagus argus) in the Matang Mangrove Forest Reserve in Peninsular Malaysia. The ratios from fish samples along with those obtained from samples of their potential food items (i.e., mangrove leaves in the estuary, coastal phytoplankton, microphytobenthos) revealed wide variations, indicating that S. argus utilizes various food items between the coastal area at the river mouth to the inner mangrove estuary. The carbon isotope ratio in the fish body tended to be lower in fish sampled from the inner estuary as compared with fish at the river mouth. The carbon isotope ratio values of the fish body were relatively high in small fish (＜20 mm in total length [TL]) but lower in fish of 20-100 mm TL, and relatively higher in fish ＞100 mm TL. These findings strongly suggest that small-sized S. argus (＜20 mm TL) migrate from the outer coastal area into the mangrove estuary and utilize the mangrove estuary habitat as their nursery grounds before eventually returning to the river-mouth area as their growth progresses.

We analyzed the gonadal development and age of the spotted scat (Scatophagus argus) in the Matang Mangrove Forest Reserve, Malaysia. Histological analysis of gonads indicated that few females and males in the mangrove estuarine system were sexually mature, with few specimens having sizes greater than the typical maturation size (> 140 mm in total length for females, > 110 mm in total length for males). These observations suggested that S. argus do not mature sexually in the mangrove estuary. Growth analysis using age information from otolith increments suggested that S. argus moved or are carried into the mangrove estuary during the late tholichthys larval stage at a size of about 12 mm-14 mm in total length (ca. 37 days old), and that the fish use the estuary as a nursery ground before sexual maturation. The period of sojourn in the estuary is for a maximum of ca. 290 days for females by the size of ca. 160 mm-180 mm in total length and ca. 155 days for males by the size of ca. 110 mm in total length. After these nursery periods, grown specimens reaching sexual maturity are considered to leave the estuary habitats.