A glimpse into the bio-physical environment of the sea louse (Lepeophtheirus salmonis (Krᴓyer 1837)) digestive tract

Abstract

The environment of the digestive tract of the sea louse Lepeophtheirus salmonis has been neglected as an area of research by sea lice researchers, with very few studies being carried out on digestion and osmoregulation in sea lice. This study presents an investigation into the environment of the digestive track in fed and starved sea lice. As well as a comparison of the contents of the digestive tract in regard to haemoglobin in sea lice that had frank blood present in their digestive system compared to sea lice that that did not appear to have ingested any blood. It was found that starved sea lice had a digestive tract that was osmotically very close to seawater. Probably due to the high buffering capacity of seawater. Even in lice that could be observed with a digestive tract that contained blood, the haemoglobin level was surprisingly low around 335 mg/dl−1. Lice that had been feeding on salmon had a digestive tract osmolarity of 815 mOsm kg−1 compared to 988.9 mOsm kg−1 in starved animals. Suggesting that about 28% of the gut contents was food material and 72% was seawater. In lice placed in a hypoosmotic environment the osmolarity of starved lice's digestive tract fell to 700 mOsm kg−1 matching that of 25 ppt seawater. This observation combined with the measurements of the haemolymph in this study confirms sea lice are osmoconformers as the haemolymph closely followed the osmolarity of the environment (35 ppt or 25 ppt seawater) the lice were in. In conclusion the digestive tract is an important organ for maintaining homeostasis and further research is required to understand the digestive and osmoregulatory role the digestive tract provides.