The effects of salinity on the gastric emptying time (GET) and absorption of nutrient along the alimentary tract of tiger
grouper (TG) × giant grouper (GG) (Epinephelus fuscoguttatus × E. lanceolatus) hybrid were studied. Juveniles TG×GG
hybrid grouper (10.0 ± 0.5 cm total length; 50.5 ± 2.0 g) were reared in different salinities (10, 15, 20, 25 and 30 parts per
thousand (ppt)) and fed with commercial pellet diet during the 60-day experimental period. The fish were then slaughtered
sequentially at different time intervals after initial feeding to obtain GET. Our results showed that low salinity (10-20 ppt)
lead to a shorter GET in the hybrid grouper. The shortest and longest GETs were observed in 15 ppt (12 h) and 30 ppt (18
h) treatments, respectively. Apparent digestibility coefficient (ADC) using ash contents was measured to determine the
absorption of nutrient in each treatment. The absorption of macronutrient in TG×GG hybrid grouper was increased as
the salinity decreased. The highest absorption occurred in 15 ppt (72% protein, 75% lipid, 68% carbohydrate and 74%
energy) while the lowest absorption occurred in 30 ppt (59% protein, 64% lipid, 34% carbohydrate and 55% energy).
The findings of this study suggested that 15 ppt salinity facilitates faster digestion and maximize the nutrient absorption
of TG×GG hybrid and may enhance the growth rate of this newly developed grouper species.
The study was conducted at Merambong Shoal (01°19.979’N, 103°35.965’E) in the Sungai Pulai estuary, Johor Straits, Malaysia from January to December 2005. Standing biomass of male and female Strombus canarium sub populations was calculated monthly based on the abundance value of each cohort and on the length-weight relationship. Secondary production was estimated using increment summation method, upon recognition of cohorts following the size-frequency distribution analysis using Bhattacharya and Hasselblad’s NORMSEP methods. Monthly variations in standing biomass
(B) and production (P) showed higher values during the wet season compared to dry season, which indicate seasonal variations. Total production (P) was estimated at 0.14 gAFDWm-2yr-1 and 0.45 gAFDWm-2yr-1, while the annual mean population biomass was estimated at 0.13 gAFDWm-2 and 0.26 gAFDWm-2, for males and females, respectively. The P/ ratio was therefore calculated at 1.08 yr-1 for male and 1.73 yr-1 for female, which was within the values reported for other gastropod species. Estimates using empirical methods commonly used in secondary production studies found
that none could be applied to the species. Considering the large amount of time, effort and resources involved in the conventional production estimation method, more studies are needed to establish a reliable production estimates for S. canarium, and possibly other gastropod species within the tropical region.
A total of 230 individuals of Strombus were sampled at various locations along the Johor Straits, Malaysia. There were four species of Strombus present in the study areas i.e. Strombus canarium Linnaeus, 1758; Strombus urceus Linnaeus, 1758; Strombus marginatus subspecies succinctus Linnaeus, 1767; Strombus marginatus subspecies robustus Sowerby, 1874; and Strombus vittatus subspecies vittatus Linnaeus, 1758. Strombus canarium was the most common, widely distributed and most abundant, followed by S. urceus, while the others were only rarely found. Among the species Strombus marginatus and Strombus vittatus were two new distribution records for the Johor Straits. Since all Strombus were traditionally harvested and consumed by the locals since long ago, further studies are needed particularly regarding the population dynamics and fishery of the harvested species.
Growth, mortality and recruitment of the sergestid shrimps Lucifer intermedius, collected from the Sungai Pulai seagrass area in Johor, Peninsular Malaysia was investigated between April 2007 and December 2007 using monthly length-frequency data. The shrimps were collected during the day by subsurface towing of a Bongo net with a mesh size of 500 μm for 30 minutes. Total length was measured monthly for 50 individuals and the estimated extreme length was 10.42 mm. The von Bertalanffy growth parameters, K and L∞ were estimated as 1.40 yr-1 and 11.10 mm, respectively. The growth performance index (φ’) was 2.237 while total mortality (Z) was calculated at 5.32 yr-1. The natural and fishing mortality was 2.99 yr-1 and 2.33 yr-1, respectively. The recruitment pattern of L. intermedius was continuous throughout the year with two major peaks. The exploitation rate (E) was estimated at 0.44. This indicates that fishery status of L. intermedius in the Sungai Pulai sea grass area of Johor Strait is below the optimum level of exploitation (E < 0.50).
The abundance of marine benthic organisms often exhibits distinct distributional patterns, which is generally governed by many physical and biological factors specific to the habitat. In this study, the spatial and temporal variations in abundance of the dog conch, Strombus canarium Linnaeus 1758, a commercially important marine gastropod, was investigated. Assessment of conch abundance at Merambong seagrass bed, Malaysia, was conducted using a transect belt method. Sampling stations were randomly selected and environmental parameters associated with the habitat were recorded. The species showed distinct spatial distributional pattern. Conch densities were significantly higher in sheltered areas, mainly in mixed seagrass bed dominated by Halophila spp. and with high sediment organic content. The densities were relatively very low in areas dominated by the tape seagrass, Enhalus acoroides. The species studied also showed distinct temporal variation in abundance. The abundance value was seasonally varied with highest density recorded during the wet monsoon season (p<0.05). The densities were otherwise very low during the dry season, except for a slight peak in July. Since the conch is a very important fishery species within the Johor Straits and regulations on their harvesting is still lacking, this information would be very important for their sustainable management.