Gill fouling in the economically important freshwater shrimp Macrobrachium rosenbergii (De Man, 1879) (Caridea: Palaemonidae)

The giant freshwater prawn, Macrobrachium rosenbergii (De Man, 1879), lives in freshwater environments of the Indo-West Pacific region and is commonly farmed. Males transition into three male morphotypes that differ in behavior and morphology. Small-clawed males (SM) molt into orange-clawed males (OC) that molt into the harvested and largest blue-clawed males (BC). Grooming behaviors can remove fouling such as sediment particles, bacteria, and other organisms, all of which are commonly found in the natural environment as well as in aquaculture environments. Because individuals of this species groom their bodies frequently, especially the gills, the objective of the study was to observe gills of male morphotypes and females and evaluate their fouling levels and types using light microscopy, bacterial counts, and scanning electron microscopy. The male morphotypes and females are fouled differently, with grooming behaviors being effective in removing sedimentary and bacterial fouling from the gills. Although their relative efficiencies in removing fouling materials from the gills were not statistically significant, OC and BC exhibited contrasting gill fouling patterns with higher bacterial than sedimentary fouling in the former but the opposite in the latter. This difference may be attributed to differential levels of fouling related to variation in behavioral priorities, grooming behaviors, and morphology. Control of bacterial and sedimentary fouling in aquaculture could have large implications on the quality and survival of harvested individuals.