Rachel R. Leads | Geology Reports

USGS2026

Comparison of nonlethal techniques as indicators of lipid content in Lake Whitefish

Objective Energetic reserves are important indicators of the relative health of fish and fish populations. Body condition indices that relate fish weight to length are commonly used as quick, noninvasive methods for approximating lipid content and condition. A microwave meter (i.e., fat meter or energy meter) is a noninvasive method found to be more accurate in some species. The objective of this study was to evaluate the suitability of nonlethal techniques for estimating muscle lipid content in Lake Whitefish Coregonus clupeaformis . Methods We compared the sensitivity of three nonlethal indicators of lipid content to laboratory-extracted muscle lipid content in Lake Whitefish, including readings from a handheld microwave meter at several positions, Fulton’s condition factor, and relative weight. Results We found significant, positive relationships between lipid content and each estimation method, except relative weight, with weak to moderate correlations. The microwave meter was moderately correlated to lipid content when positioned anterior to the dorsal fin above the lateral line ( r 2 = 0.50), while other positions and combinations of positions had weaker correlations ( r 2 range = 0.27–0.45). Correlation was only slightly improved by including additional model variables (i.e., length and weight). Fulton’s condition factor was weakly correlated with lipid content ( r 2 = 0.19), while relative weight was not significantly correlated with lipid content. Conclusion The microwave meter provides an improvement to muscle lipid estimation compared with length–weight body condition indices; however, microwave meter readings alone do not constitute a reliable predictive measure for true muscle lipid content under the conditions tested here. We hypothesize that the low strength of correlation may be due to low muscle lipid content or the presence of thick scales in Lake Whitefish. Further investigation is needed to understand the mechanisms negatively affecting the predictive performance of the microwave meter in Lake Whitefish and other species.

Michigan↗

USGS2025

Influence of cardiotoxicity on visual function in developing zebrafish ( Danio rerio ) exposed to Deepwater Horizon crude oil

Polycyclic aromatic hydrocarbons (PAHs) are toxic constituents of crude oil that can induce cardiac dysfunction and vision impairment in early life stage (ELS) fishes. However, it is currently unknown whether visual impairments are independent effects or if they result from underlying PAH cardiotoxicity. To better understand this mechanism, microinjection of microRNA 133b (miR133b) was used to impair cardiac development in ELS zebrafish (injected at <1.25 hpf). Vision and cardiac endpoints were compared between miR133b-injected and oil-exposed zebrafish (4–72 hpf, 54.68–60.41 µg/L tPAH 50 ) to determine the influence of cardiac dysfunction and oil exposure on visual function. At 7 dpf, pericardial area and eye area were measured, and visual function was assessed by optokinetic response (OKR). Over 94 % of miR133b larvae and 45 % of oil-exposed larvae exhibited pericardial edema. Across treatments, there was a strong negative linear correlation between pericardial area and eye area ( r =-0.839, p < 0.0001). All miR133b larvae that exhibited pericardial edema and 18 % of the oil-exposed larvae that exhibited pericardial edema also exhibited reduced eye area (microphthalmia). In both the miR133b and oil groups, OKR was significantly reduced in larvae exhibiting pericardial edema ( p < 0.0001) and in larvae exhibiting reduced eye area ( p < 0.0001). A negative binomial generalized linear model (GLM) indicated that reduced eye area ( p < 0.0001), rather than pericardial edema ( p = 0.76), was a significant predictor of OKR. However, pericardial edema was strongly correlated with reduced eye area across treatments. These results suggest that visual effects may result from an interaction of cardiotoxicity as well as direct impacts to the visual system.

Aquatic Toxicology↗