Fish health management in cage aquaculture

Finfish is the primary source of animal protein for humans in many parts of the world and per capita consumption of fish has been increasing from an average of 9.9 kg in the 1960s to 19.2 kg in 2012 (FAO, 2014). Growing global population, dwindling natural fish stocks, and the increasing demand are the major drivers for increasing fish production. Aquaculture remains the only option to meet these demands and globally, the share of aquaculture is projected to rise to 62% of the total fish production by 2030. However, considering the limitations of the traditional aquaculture systems due to environmental issues, carrying capacities etc., it has been recognized that cage culture, especially mariculture has many advantages. Over the years, cage culture has become one of the economically viable methods of large-scale production of high-value food fishes

Volatilization of inorganic mercury by Isochrysis galbana Parke from aquatic system

The loss of mercury added cxtraneously as an inorganic source to the algal cultures (Jsochrysis sp.) and to the seawatcr containing in situ phytoplankton populations off Cochin was determined quantitatively. Such loss of mercury was attributed to uptake as well as volatilisation of mercury (Hg") by the activity of phytoplankton and micro - organisms. The rate of removal of mercury in the culture system was 54% per day and that by in situ phytoplankton was 38

Distribution of luminescent Vibrio harveyi and their bacteriophages in a commercial shrimp hatchery in South India

Luminescent Vibrio harveyi is a natural microflora of marine and coastal water bodies and is associated with mortality of larval shrimp in penaeid shrimp hatcheries. It is also known that the bacteriophages occur virtually in all places where their hosts exist. In this study, distribution of luminescent V. harveyi and the bacteriophages affecting these hosts was examined in a commercial Penaeus monodon hatchery during three shrimp larval production cycles, including a cycle affected by luminescent bacterial (LB) disease outbreak

Effect of temperature and salinity on the infectivity pattern of white spot syndrome virus (WSSV) in giant tiger shrimp Penaeus monodon (Fabricius, 1837)

White spot disease (WSD) caused by the lethal white spot syndrome virus (WSSV) continues to be the major cause of mortality among farmed tiger shrimp in India and elsewhere, resulting in an annual loss of about 4-6 billion US$. Among the environmental variables, temperature and salinity of the rearing water are considered to be major triggering factors for white spot disease outbreak. In order to characterise the effect of salinity and temperature on the pathogenecity of WSSV infection in giant tiger shrimp Penaeus monodon, a laboratory challenge study was conducted at different levels of temperature (16, 25, 27, 28, 30, 32 and 36 ºC) and salinity (0.5, 5, 10, 15, 30 and 45 g l-1) with virulent white spot syndrome virus. Significant influence of temperature (p<0.05) on the percentage mortality and time until death of shrimp affected by the virus was observed, whereas salinity did not show any effect. Significantly higher survival rate was recorded in animals exposed at 32 ºC (37%) and 36 ºC (14%), 21 days post-challenge (dpc). All the shrimp challenged at other temperature levels, however, died after 21 dpc. These results demonstrated preference of WSSV for lower temperatures and higher survival in temperature ranges of 32 ºC to 36 ºC. The present observation may help to develop a management option to control the WSSV inflicted mortalities by selecting favorable hyperthermic rearing conditions for the shrimp

Histopathology of Y-organ in Indian white shrimp Fenneropenaeus indicus, experimentally infected with white spot syndrome virus

Histopathology of Y-organ (moulting gland) in Indian white shrimp Fenneropenaeus indicus was studied after challenging the shrimp with virulent white spot syndrome virus (WSSV). Histopathological investigation on the Y-organ collected from moribund shrimps revealed the presence of intranuclear basophilic inclusions, characteristic of WSSV. More than 70% of the Y-organ cells were infected, suggesting the degenerated state of the organ. The cellular integrity of the Y-organ was completely destroyed by the WSSV. Further, Y-organ tissue samples collected from all the 16 experimental shrimp were positive by one-step polymerase chain reaction (PCR), confirming severe WSSV infection. The infected Y-organ in F. indicus with majority of the organ cells observed in the lysed condition suggests a physiological dysfunction of the organ. In uninfected and healthy controls, the lobulated Y-organ showed closely packed normal cells with prominent nuclei and sparse cytoplasm. Physiological implication of a degenerated Y-organ in the moulting and reproduction of the penaeid shrimp is discussed

Inhibition of primary production as induced by heavy metal ions on phytoplankton population off Cochin

The effect of five metals (Cd, Ni, Cr, Pb and Hg) at different concentrations below and above tolerance limits, in the primary productivity off Cochin was investigated. It was observed that cadmium, nickel, lead, chromium and mercury even at low concentrations were found inhibiting the primary productivity. Among the metals tested, nickel apfieared to be the least toxic and mercury the most toxic in their inhibitory effect. It was evident that the synergistic effect of inhibition was more acute when the metals were present in combination than each metal individually

Involvement of Enterobacter cloacae in the mortality of the fish, Mugil cephalus

Enterobacter cloacae, an enteric bacterium that belongs to the family Enterobacteriaceae, is widely distributed in nature. It is found in faeces of humans and animals, water, soil, plants, plant materials, insects and dairy product