SeaBird CTD

The SeaBird SBE 25plus supports several sensors including SBE-3/SBE-4 temperature and conductivity sensors, and Sea-Bird Scientific auxiliary sensors — dissolved oxygen, pH, fluorescence, oil, radiance (PAR), light transmission, turbidity, nitrates. The CTD is battery operated, and can withstand deep sea measurements.

https://www.seabird.com/profiling/sbe-25plus-sealogger-ctd/family?productCategoryId=54627473768