Aquaculture & Fisheries

Biography

Biography: Nelly Wabete

Abstract

Shrimp farming is an important economical sector in New Caledonia based on a non indigenous domesticated species, the Pacific Blue Shrimp Litopenaeus stylirostris. Animals with orange gills have been observed recently in grow-out ponds and up to 70% of the shrimp in one pond could be affected. This coloration impacts the quality product in the processing plant, leading to less-value shrimp for farmers. The phenomenon occurred when the average weight of shrimp is around 18g and after 80 days of rearing, concomitantly with a high feeding rate and an important phytoplanctonic biomass. Temporal fluctuations in gills coloration were also noticed. Individual observations allowed to conclude that gills coloration intensity varies according to the intermoult stages, from white in postmolt stage to a deep orange in premolt stage and disappeared after the molting (figure 1). Orange gills percentage was greatly reduced in shrimp population by isolating them from the soil with floating cages in earthen impacted ponds. Histological, biochemical and scanning electron microscopy (SEM) studies have shown that heterogeneous iron layers were settled on the tissue surface and the iron concentration was tenfold higher in the orange gills than in white ones. Some bacterial colonisations have also been observed and are assumed to be involved in the iron precipitation processes which lead to these orange colorations. Very high concentrations in dissolved iron (till 70μM) were measured in the sediment pore water suggesting an environmental triggering of the phenomenon. All these results raise questions about the impact of orange gills on shrimp health, and in which conditions this phenomenon is promoted.