Transcriptomic variations associated with salinity stress in Penaeus indicus.

BACKGROUND: The Indian white shrimp, Penaeus indicus a native species of India, is important brackishwater aquaculture species. Shrimps are euryhaline in nature and they regulate osmotic and ionic concentrations by osmoregulatory process. However, variations in abiotic factors such as salinity result in stress to the shrimps during culture period affecting their growth and immunity. METHODS AND RESULTS: To understand the adaptive mechanism to stress in low salinity conditions, RNA-seq was used to compare the transcriptomic response of P. indicus upto 3 weeks. De novo assembly using Trinity assembler generated a total of 173,582 transcripts. The assembly had a mean length of 854 bp, N50 value of 1243 bp and GC content of 42.33%. Differential gene expression analysis, resulted in identification of 2130, 3090, and 5351 DEGs in 7 days, 14 days and 21 days respectively of salinity stress period. The pathway prediction of the assembled trinity transcripts using KEGG database showed total number of 329 pathways linking 12,430 transcripts. KEGG pathway enrichment analyses led to the identification of several enriched pathways related to lipid metabolism, amino acid metabolism, glycolysis, signalling pathways etc. Selected genes involved in osmoregulatory process and immune response in shrimps were validated and analysed for the gene expression levels by quantitative real-time PCR (qPCR). CONCLUSION: This study on the adaptive transcriptomic response of P. indicus to low salinity, will further help in our understanding of the molecular mechanisms underlying osmoregulation mechanism in shrimps.

The effect of acclimation temperature and optimal temperature gradient for egg and larvae of silver moony (Monodactylus argenteus) during the early ontogenesis.

The early life history of a fish species is regulated by temperature, the most critical environmental cue. Thus, identifying the gradient of temperature that optimises the early development of a species is a prerequisite for standardising hatchery technology. Silver moony, Monodactylus argenteus is a tropical brackishwater ornamental fish that holds scope for the Indian and Global ornamental fish industry. This study unravels the effect of water temperature increments (26, 28, 30, 32, and 34 °C) on embryonic development, hatching, and survival rate, as well as the growth profile and survival rate of larvae at 5 days post-hatch (5 dph). Experiments were conducted to find out the optimal temperature gradient for egg incubation and early larval rearing. The experiment results revealed that the embryogenesis was accelerated at increasing temperatures, especially after the gastrula stage, and apparent differences were evident in each stage. However, the morphological development profile at each embryonic stage was similar throughout the temperature range. The incubation period differed significantly (P < 0.05) between the temperature gradients. The highest rates of hatching (90-100%) and survival after 12 hph were observed at 28 ºC and 30 ºC. Hatched-out larvae demonstrated the highest total length (1.92 ± 0.02 µm) at 34 °C, and the total length decreased at lower temperature levels. The yolk sac volume of larvae was shrunken with an increase in temperature, and a significant difference was observed between the studied temperatures. However, the oil globule diameter did not differ between the different temperatures. The total length and growth rate of 5 dph larvae were significantly different among the temperature treatments and increased with increasing temperature. In contrast, the survival rate of 5 dph larvae was highest at the range of 26 ºC and 30 ºC. The results indicated that the change in temperature from the spawning temperature (29 ± 1 °C) negatively influenced embryogenesis and the early development of M. argenteus. Based on the experimental results, the growth and survival of embryo and larvae were found to be optimum at 28 to 30 ºC. This prediction is of great importance for the effective management in the hatchery production phase, and especially the temperature could be considered the critical environmental cue.