Dong-Fang Deng

Contaminant concentrations and histopathological effects in Sacramento splittail (Pogonichthys macrolepidotus).

Sacramento splittail (Pogonichthys macrolepidotus) is a species of special concern in California, due to multiple anthropogenic stressors. To better understand the potential impact of contaminant exposure, adult splittail were captured from the Sacramento-San Joaquin River Delta (California, USA) and analyzed for histopathology and contaminant exposure. Organochlorine contaminants (PCBs, DDTs, dieldrin, chlordanes, and PBDEs) and trace metals (Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Sn, V, and Zn) were detected in the tissues of all fish. In many samples, human health screening values were exceeded for PCBs (83 of 90 samples), DDTs (32 samples), and dieldrin (37 samples). In contrast, thresholds for fish effects were rarely exceeded. Histopathological analysis indicated the presence of macrophage aggregates in gonads, kidneys, and liver and a high incidence of liver abnormalities. In the liver, observed effects were often moderate to severe for glycogen depletion (55 of 95 fish), lipidosis (hepatocellular vacuolation; 51 fish), and cytoplasmic inclusion bodies (33 fish). Correlations between histopathology and tissue contaminant concentrations were weak and inconsistent. Significant correlations were observed between histopathology indicators and reductions in fish size, body condition, lipid content, and liver weight. These results suggest that splittail histopathology varies as a function of health and nutritional status, rather than exposure to legacy organic and metal pollutants.

Selenocompounds in juvenile white sturgeon: evaluating blood, tissue, and urine selenium concentrations after a single oral dose.

Selenium (Se) is an essential micronutrient for all vertebrates, however, at environmental relevant levels, it is a potent toxin. In the San Francisco Bay-Delta, white sturgeon, an ancient Chondrostean fish of high ecological and economic value, is at risk to Se exposure. The present study is the first to examine the uptake, distribution, and excretion of various selenocompounds in white sturgeon. A combined technique of stomach intubation, dorsal aorta cannulation, and urinary catheterization was utilized, in this study, to characterize the short-term effects of Se in the forms of sodium-selenate (Selenate), sodium-selenite (Selenite), selenocystine (SeCys), l-selenomethionine (SeMet), Se-methylseleno-l-cysteine (MSeCys), and selenoyeast (SeYeast). An ecologically relevant dose of Se (∼500 μg/kg body weight) was intubated into groups of 5 juvenile white sturgeon. Blood and urine samples were repeatedly collected over the 48 h post intubation period and fish were sacrificed for Se tissue concentration and distribution at 48 h. The tissue concentration and distribution, blood concentrations, and urinary elimination of Se significantly differ (p ≤ 0.05) among forms. In general, organic selenocompounds maintain higher blood concentrations, with SeMeCys maintaining the highest area under the curve (66.3 ± 8.7 and 9.3 ± 1.0 μg h/ml) and maximum Se concentration in blood (2.3 ± 0.2 and 0.4 ± 0.2 μg/ml) in both the protein and non-protein bound fractions, respectively. Selenate, however, did not result in significant increase of Se concentration, compared with the control, in the protein-bound blood fraction. Regardless of source, Se is preferentially distributed into metabolically active tissues, with the SeMet treated fish achieving the highest concentration in most tissues. In contrast, Selenite has very similar blood concentrations and tissue distribution profile to SeCys and SeYeast. From blood and tissue Se concentrations, Selenate is not stored in blood, but taken up rapidly by the liver and white muscle. Urinary elimination of Se is form dependent and peaks between 3 and 12 h post intubation. A basic understanding of the overall Se absorption, distribution, and elimination is provided through monitoring tissue Se concentrations, however, conclusions regarding to the dynamics and the specific processes of Se metabolism can only be inferred, in the absence of kinetic information.

Sublethal dietary effects of Microcystis on Sacramento splittail, Pogonichthys macrolepidotus.

The presence of the toxic cyanobacterium Microcystis in the upper San Francisco Estuary (SFE) since 1999 is a potential but to date an unquantified threat to the health and survival of aquatic organisms, such as fish and zooplankton. The microcystins (MCs) predominantly in the LR-form (MC-LR) contained in Microcystis is hepatotoxic and a potential threat to the fishery. This study was conducted to determine the effects of dietary exposure of the endemic Sacramento splittail, Pogonichthys macrolepidotus in SFE to Microcystis and its toxin, MC-LR. Juvenile splittail (12.59 ± 0.7 g fish(-1)) were exposed to five diets for 28 d with MC-LR obtained from: (1) Microcystis harvested from the SFE and (2) a synthetic purified form of MC-LR. Three of the test diets contained 3.55 (D5), 9.14 (D10) and 17.13 (D20)mg MC-LR kg(-1) from Microcystis. The other two diets contained either purified MC-LR at 3.89 mg MC-LR kg(-1) (D5R) or no MC-LR (D0). The RNA/DNA ratio of fish muscle was significantly lower for all treatments fed test diets containing MC-LR compared to the control diet D0, suggesting Microcystis adversely affected nutritional status. Protein phosphatase 2A expression in the fish from the D5, D10 and D20 treatments were inversely affected by increasing concentrations of MC-LR. Cytoplasmic inclusion bodies and single cell necrosis were more prevalent and greater in severity in the fish exposed to the diets D10 and D20 compared to fish from the D0 treatment and indicate severe liver toxicity in splittail exposed to MC-LR. The sublethal effects on splittail characterized by this study suggest cyanobacterial blooms have the potential to affect splittail nutritional status and health in SFE.

Responses of heat shock protein 70 and caspase-3/7 to dietary selenomethionine in juvenile white sturgeon

An 8-week feeding trial was conducted to investigate the responses of juvenile white sturgeon (Acipenser transmontanus) to elevated dietary selenium (Se) based on the determination of the RNA/DNA ratio in muscle, heat shock protein 70 (Hsp70), and caspase-3/7 in muscle and/or liver tissues. Four semi-purified test diets were prepared by adding different levels of L-selenomethionine (0, 50, 100, and 200 mg/kg diet). The analytical determinations of total Se were 2.2, 19.7, 40.1, and 77.7 mg/kg diet. The sturgeon (initial body weight: 30 ± 2 g; mean ± SEM) were raised in indoor tanks provided with flow through freshwater (18–19 °C). There were three replicates for each dietary treatment with 25 fish per replicate. The liver and muscle tissues were collected at 4 and 8 weeks after feeding the test diets. A significant interaction between duration and levels of dietary Se exposures on RNA/DNA ratio in the muscle tissue was detected (P < 0.05). Although there was no significant main effect due to the duration of dietary Se exposures (i.e., 4 weeks versus 8 weeks) on muscle RNA/DNA ratio (P ≥ 0.05), the ratio was significantly decreased with increasing dietary Se levels. Significant main effects were caused by the duration and levels of dietary Se exposures on Hsp70 in both the muscle and liver tissues, with significant increases in Hsp70 due to a longer exposure (8 weeks) and higher levels (40.1 and 77.7 mg Se/kg diet) of dietary Se. The caspase-3/7 activity in the liver were significantly higher in fish fed the diets containing 40.1 and 77.7 mg Se/kg diet than those fed the other diets. The toxic thresholds of Se in the muscle were estimated to be 32.2 and 26.6 mg Se/kg for the depressed specific growth rate and the induced Hsp70 response in muscle, respectively. This result indicated that the Hsp70 response in muscle is a more sensitive biomarker than the SGR of sturgeon for evaluating Se toxicity in white sturgeon. Results of the current study suggest that a mechanism involved with the activation of stress protein production and apoptosis protects white sturgeon from the lethal effect of Se.