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

Authors: BRICKNELL, IAN - University Of Maine; Pietrak, Michael

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: 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 of sea lice that had visible 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 with a pH only slightly lower than that of 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 hemoglobin level was surprisingly low. Lice that had been feeding on salmon had a digestive tract osmolarity that was reduced compared to starved animals. Suggesting that about 28% of the gut contents was food material and 72% was seawater. In lice placed in a lower salinity environment the osmolarity of starved lice’s digestive tract fell to match that of 25ppt 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 (35ppt or 25ppt seawater) the lice were in. In conclusion the digestive tract is an important organ for maintaining equilibrium and further research is required to understand the digestive and osmoregulatory role the digestive tract provides.

Technical 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 hemoglobin 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 with a pH of 8.15 only slightly lower than that of 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 hemoglobin 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 25ppt 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 (35ppt or 25ppt 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.