Complex sentence: Like its relative the oilfish ("Ruvettus pretiosus"), it cannot metabolize the wax esters (Gempylotoxin) naturally found in its diet, which accumulates to give an oil content in the muscle meat of 18--21%.
Split into simpler sentences: Like its relative the oilfish ("Ruvettus pretiosus"), it cannot metabolize the wax esters (Gempylotoxin) naturally found in its diet. These waxy oils accumulate to give an oil content in the muscle meat of 18--21%.