DEVELOPING A NON-INVASIVE METHOD TO ASSESS GREEN STURGEON (ACIPENSER MEDIROSTRIS) CONDITION.  

Non-invasive methods to determine sturgeon condition are needed for both aquaculture and sturgeon conservation.  Our aim was to determine whether a Distell fish fatmeter could be used for reliable assessment of green sturgeon condition.  There is no documented use of this technology with sturgeon species.  To establish the relationship between lipid content and fatmeter reading, we conducted a laboratory experiment on green sturgeon held in captivity at the Conte Anadromous Fish Research Center.  Thirty sexually-immature sturgeon (age 8, total length 75.1 - 114 cm, weight 1.9 - 7.4 kg) were held in Connecticut River water at 14ºC, and under five different feeding rates: 0.1%, 0.25%, 0.5%, 1.0%, 1.5% of body weight/d.  All experimental sturgeon carried a previously implanted Passive Integrated Transponder (PIT) that provided unique identification.  We conducted proximate composition analysis on muscle tissue of sacrificed animals, along with fatmeter readings, after 167-169 days.  Muscle fat content was determined via supercritical fluid extraction (SFE) using carbon dioxide and an ethanol modifier.  Five fatmeter measurements were taken at each of three different sites along the dorsal flank above the lateral line.  Four sturgeon died of causes unknown.  One sturgeon from the 0.25 % body weight/d treatment died on day 89, and 3 from the 1.0 % body weight/d treatment died on days 147, 149, and 149.  These fish were excluded from the analysis.  For all treatments, mean total length increased between the initial sample and the end of the experiment.  However, fish fed the lowest ration decreased in mean weight and condition factor.  As expected, hepatosomatic index (liver weight /body weight x100 %) increased with feeding ration.  Additionally, muscle protein content was positively correlated with ration, and inversely correlated with muscle moisture content.  In spite of a wide range of resulting individual muscle lipid levels (0.5 - 3.4%), the fatmeter readings did not accurately reflect flesh lipid content (Figure 1), regardless of the position on the sturgeon body where they were taken.  The readings may have been affected by the presence of scutelets, on the skin or lack of a sturgeon-specific instrument calibration.  Further refinement of this technology is needed if it is to be used on sturgeon either in aquaculture settings or in the wild.