Effects of temperature and salinity on the survival and development of mud crab, Scylla serrata (Forsskål), larvae

The combined effects of temperature and salinity on larval survival and development of the mud crab, Scylla serrata, were investigated in the laboratory. Newly hatched larvae were reared under 20 °C temperature and salinity combinations (i.e. combinations of four temperatures 25, 28, 31, 34 °C with five salinities 15, 20, 25, 30, 35 g L−1). The results showed that temperature and salinity as well as the interaction of the two parameters significantly affected the survival of zoeal larvae. Salinity at 15 g L−1 resulted in no larval survival to the first crab stage, suggesting that the lower salinity tolerance limit for mud crab larvae lies somewhere between salinity 15 and 20 g L−1. However, within the salinity range of 20–35 g L−1, no significant effects on survival of zoeal larvae were detected (P>0.05). The combined effects of temperature and salinity on larval survival were also evident as at low salinities, both high and low temperature led to mass mortality of newly hatched larvae (e.g. 34 °C/15 g L−1, 34 °C/20 g L−1 and 25 °C/15 g L−1 combinations). In contrast, the low temperature and high salinity combination of 25 °C/35 g L−1 resulted in one of the highest survival to the megalopal stage. It was also shown that at optimal 28 °C, larvae could withstand broader salinity conditions. Temperature, salinity and their interaction also significantly affected larval development. At 34 °C, the mean larval development time to megalopa under different salinity conditions ranged from 13.5 to 18.5 days. It increased to between 20.6 and 22.6 days at 25 °C. The effects of salinity on larval development were demonstrated by the fact that for all the temperatures tested, the fastest mean development to megalopa was always recorded at the salinity of 25 g L−1. However, a different trend of salinity effects was shown for megalopae as their duration consistently increased with an increase in salinity from 20 to 35 g L−1. In summary, S. serrata larvae tolerate a broad range of salinity and temperature conditions. Rearing temperature 25–30 °C and salinity 20–35 g L−1 generally result in reasonable survival. However, from an aquaculture point of view, a higher temperature range of 28–30 °C and a salinity range of 20–30 g L−1 are recommended as it shortens the culture cycle

Effects of tank colour on larval survival and development of mud crab Scylla serrata (Forskal)

Hatchery culture of mud crabs has not yet achieved commercial viability despite decades of research efforts. Further research is therefore needed to better understand larval culture requirements of the crab. Based on anecdotal observations, an experiment was carried out to test whether the background colour of the culture vessel affected larval culture success. Newly hatched larvae of Scylla serrata were reared in culture vessels of five colours, i.e., black, dark green, maroon, sky blue and white. Larval survival and development were monitored daily until all of them either moulted to the first crab stage or died. The results showed clear effects of background colour on larval survival. A general tendency of higher larval survival in darker-coloured backgrounds was evident. In particular, overall zoeal survival for larvae reared in black vessels was significantly higher than those reared in white ones. Background colour also appeared to affect larval development. Larvae reared in darker backgrounds generally had shorter development times and more synchronized moulting. A significant delay in zoeal development was observed in larvae reared in white vessels. Dark backgrounds possibly facilitated more efficient feeding, reduced settlement of larvae at the bottom of the vessels as well as minimized stress. This result appears to be the first to demonstrate that background colour can significantly affect larval survival and development of a crustacean species.\u

Occult Hepatitis C virus infection among hemodialysis patients

Occult hepatitis C virus (HCV) infection (i.e., detectable HCV-RNA in the liver or peripheral blood mononuclear cells) in the absence of both serum HCV-RNA and anti-HCV antibodies has not been investigated in hemodialysis patients. In this study, real-time PCR and in situ hybridization was used to test for the presence of genomic and antigenomic HCV-RNA in peripheral blood mononuclear cells of 109 hemodialysis patients with abnormal levels of liver enzymes. Occult HCV infection, determined by the presence of genomic HCV-RNA, was found in 45% of the patients; 53% of these patients had ongoing HCV replication, indicated by the presence of antigenomic HCV-RNA. Patients with occult HCV infection had spent a significantly longer time on hemodialysis and had significantly higher mean alanine aminotransferase levels during the 6 mo before study entry. Logistic regression analysis revealed that mortality was associated with age >60 yr (odds ratio 3.30; 95% confidence interval 1.05 to 10.33) and the presence of occult HCV infection (odds ratio 3.84; 95% confidence interval 1.29 to 11.43). In conclusion, the prevalence of occult HCV infection is high among hemodialysis patients with persistently abnormal values of liver enzymes of unknown cause. The clinical significance of occult HCV infection in these patients requires further study

Influence of binder type on leaching rate and ingestion of microbound diets by mud crab, Scylla serrata (Forsskål), larvae

Microbound diets (MBD), composed of nutrients held within a matrix or binder, were shown to be readily ingested by larvae of the mud crab, Scylla serrata (Forsskål). In an effort to improve experimental MBD developed for S. serrata larvae, this study determined the effects of various binders on estimated larval ingestion of MBD as well as their leaching rates. Microbound diets with the same dietary compositions were bound with either agar, alginate, carrageenan, gelatin or zein. All diets contained 14C-labelled rotifers and were fed to Zoea I, III, V larvae and megalopae. The 14C content of larvae fed 14C-labelled MBD for 2 h was used to estimate the relative ingestion rates of MBD. For all larval stages tested, the estimated mean larval ingestion of MBD did not differ significantly between binder types (P>0.05). Determination of the amount of 14C-labelled nutrient leaching from MBD bound with various binders after 30, 60 and 240 min of immersion showed that for all types of binders, 14C leaching occurred primarily within the first 30 min of immersion. Zein-bound MBD consistently showed the lowest numerical leaching rate among the five binders tested for all immersion periods examined, and the differences compared with other binders were often significant, particularly after 60 and 240 min of immersion. Larval feeding experiments showed that MBD prepared with binders showing higher rates of leaching were not utilized to a greater degree by S. serrata larvae. Furthermore, unnecessary leaching from MBD particles wastes dietary nutrients and is likely to impact on water quality. On this basis, our results suggest that because of its consistently lower leaching rates, zein is probably a more suitable binder for MBD developed for S. serrata larvae