An Adult Zebrafish Diet Contaminated with Chromium Reduces the Viability of Progeny

Abstract

The lack of standardized diet for laboratory animals can have profound effects on animal health and lead to less reproducible research outcomes. Live diets are commonly used in zebrafish culture and, although they are a more natural feed than flake or pellet food, are also a potential source of pathogens and toxic compounds. Heavy metals are a group of such compounds, which can accumulate in fish leading to developmental abnormalities, reduced growth, and increased rates of mortality. Two to three weeks after feeding adult zebrafish a new lot of nonhatching decapsulated brine shrimp cysts (Decaps), embryos at the University of Minnesota Zebrafish Core Facility (ZCF) and the University of Utah Centralized Zebrafish Animal Resource (CZAR) began to exhibit an orange color in the yolk, and larval health began to decline. The concentration of chromium in the Decaps (69.6 mg/kg) was more than 30 times that of other zebrafish diets tested (up to 2.1 mg/kg) and is thought to be the cause of the observed symptoms. Within 3 weeks of removing the Decaps from the feeding regimen, the orange coloration in the yolks began to diminish, the morphological abnormalities began to subside, and larval survival rates began to increase. Thus, implementation of standardized zebrafish diets and regular feed-quality testing may help to prevent the introduction of contaminants to zebrafish research facilities.

Dietary Contaminants and Their Effects on Zebrafish Embryos

“…Contamination is so prevalent that the Utah Department of Environmental Quality has declared that there is a potential risk to human consumption of waterfowl in the area [ 17 ], which consume brine shrimp and other invertebrates that inhabit the lake [ 18,19 ]. In a recently reported study, brine shrimp cysts at the University of Minnesota and University of Utah zebrafish facilities were found to contain chromium levels more than 30 times greater than any other zebrafish diet tested [ 2 ]. Offspring from adults fed the contaminated diets exhibited orange coloration in the yolks, cardiac edema, misshapen yolk sacs, developmental delay, lack of swim bladder inflation, and high mortality [ 2 ].…”

“…Currently, the only way to analyze feed for dietary contaminants is for an individual zebrafish facility to send samples into a lab for custom analysis. Contaminants have been detected in companion animal feeds, rodent chow, and fish feeds [ 2,[12][13][14][15] ]. In most incidences, the contamination levels are well below the threshold that is considered a health risk for humans.…”

Dietary Contaminants and Their Effects on Zebrafish Embryos

“…Deleterious compounds can also enter a fish’s body via consumption of food. Live and manufactured feeds used in the culture of zebrafish have been known to contain deleterious compounds due to natural or human sourced toxins [1,2]. Absorption of nutrients, including toxins, mostly occurs in the small intestine.…”

“…Contaminants have been detected in companion animal feeds, rodent chow, and fish feeds [2,12,13,14,15]. In most incidences, the contamination levels are well below the threshold that is considered a health risk for humans.…”

“…One reported incident occurred at the University of Minnesota and University of Utah zebrafish facilities in 2016. Abnormally high levels of chromium were found in brine shrimp cysts that were fed to adult zebrafish which resulted in major malformations, discoloration, and near 100% mortality of zebrafish embryos [2].…”