Effect Threshold for Selenium Toxicity in Juvenile Splittail, Pogonichthys macrolepidotus A

In fish, selenium can bioaccumulate and cause adverse impacts. One of the fish species potentially at risk from selenium in the San Francisco Bay (California, USA) is the splittail (Pogonichthys macrolepidotus). Previous studies have derived a whole body NOAEL and LOAEL of 9.0 and 12.9 mg/kg-dw, respectively, for selenium in juveniles. However, the NOAEL/LOAEL approach leaves some uncertainty regarding the threshold of toxicity. Therefore, the raw data from the original experiment was re-analyzed using a logistic regression to derive EC10 values of 0.9 mg/kg-dw in feed, 7.9 mg/kg-dw in muscle, 18.6 mg/kg-dw in liver for juvenile splittail. Selenium concentrations in the dietary items of wild splittail exceed the EC10 values derived here. Thus, deformities previously reported in wild splittail may have resulted from selenium exposures via the food chain

Embryonic and Larval Development of Sacramento Splittail Pogonichthys macrolepidotus

Embryonic and larval development of Sacramento splittail (Pogonichthys macrolepidotus) was characterized from zygote to metamorphosis in laboratory conditions. Fertilized eggs were obtained from induced and natural tank spawning of adults caught in the Yolo Bypass of the Sacramento River. Splittail produced transparent adhesive eggs with a moderate perivitelline space. Duration of embryonic development from fertilization to hatching was 100 h at 18 ± 0.5 °C. Newly hatched larvae were 5.2 to 6.0 mm total length with no mouth opening. Yolk-sac larvae were demersal and absorbed the yolk within 10 days post-hatch. Exogenous feeding started at 6 days post-hatch, concomitant with swim bladder inflation and swim-up movement. Fin differentiation began at approximately 10 d post-hatch (ca. 8.3 to 8.85 mm total length) and was completed at 50 d post-hatch (ca. 19.6 to 20.85 mm total length) when larval finfold was fully resorbed and the adult complement of fin rays was present in all fins, but scales were still lacking.

Heat Shock Protein 70 (HSP70) responses in tissues of white sturgeon and green sturgeon exposed to different stressors

A factorial experiment was conducted to compare the responses of heat shock protein 70 (Hsp70) in seven different tissues of White Sturgeon Acipenser transmontanus and Green Sturgeon A. medirostris after they were exposed to four different stressors. Three White Sturgeon (2.3 ± 0.1 kg [mean ± SE]) and three Green Sturgeon (2.3 ± 0.1 kg [mean ± SE]) were each subjected to one of four different stressors, after which the Hsp70 levels in seven different tissues were measured using Western blot. The four stressors were heat shock, cold shock, air exposure, and food deprivation; and the seven tissues sampled were mucus, heart, liver, gastrointestinal tract, gill, spleen, and white muscle. We also sampled tissues of three White Sturgeon and three Green Sturgeon without any stressor, and measured their Hsp70 levels as a control. We compared Hsp70 responses of the stressed sturgeon with those of the control, which was set at 100%, and found that Hsp70 responses were significantly (P < 0.05) affected by the different stressors and also varied significantly among the tissues. For both species of sturgeon, heat shock was shown to be the most effective stressor inducing Hsp70 responses and mucus was the most responsive tissue. Under heat shock stress, Hsp70 responses in all tissues except liver were significantly higher in the White Sturgeon than in the Green Sturgeon. When both species of fish were exposed to heat shock, cold shock, or food deprivation, White Sturgeon showed significantly higher Hsp70 responses in mucus than did Green Sturgeon. In summary, heat shock elicited the highest Hsp70 responses and mucus was the most sensitive tissue. Based on the tissue Hsp70 responses, White Sturgeon were predicted to have a better defense mechanism against heat shock than Green Sturgeon

The Effect of feeding rate on the growth performance of green sturgeon (<i>Acipenser medirostris</i>) fry

Four one-week growth trials were conducted on green sturgeon fry to determine the effect of feeding rate on their growth performance at 18 °C when they were fed a salmonid soft moist feeds containing 445–457 g kg−1 of crude protein and 201–207 g kg−1 of lipid. The fry used in Trials I-IV were 5–8 weeks after their initiation of exogenous feeding. Their average initial body weights were 1.63 ± 0.01, 2.63 ± 0.03, 5.08 ± 0.08 and 7.49 ± 0.05 g, respectively. Six feeding rates used were as follows: 2.5–15.0% body weight per day (% BW day−1) with a 2.5% increment in Trial I; 1.25–7.50% BW day−1 with a 1.25% increment in Trial II; and 2.0–7.0% BW day−1 with a 1.0% increment in Trials III and IV. Four replicates with 50 fry per tank in Trials I-III and 30 fry per tank in Trial IV were assigned randomly to each feeding rates. The final body weight, specific growth rate, feed efficiency, protein retention, and whole-body moisture, lipid, and energy contents were significantly (P &lt; 0.05) affected by the feeding rates. The optimum feeding rates determined by the broken-line model were 7.1, 5.7 and 5.3% BW day−1 for Trials I, II and IV, when the fry were 5, 6 and 8 weeks after their initiation of exogenous feeding, respectively

Effect of dietary selenomethionine on growth performance, tissue burden, and histopathology in green and white sturgeon

A comparative examination of potential differences in selenium (Se) sensitivity was conducted on two sturgeon species indigenous to the San Francisco Bay-Delta. Juvenile green (Acipenser medirostris), recently given a federally threatened status, and white sturgeon (Acipenser transmontanus) were exposed to one of four nominal concentrations of dietary l-selenomethionine (SeMet) (0 (control), 50, 100, or 200 mg SeMet/kg diet) for 8 weeks. Mortality, growth performance, whole body composition, histopathology, and Se burdens of the whole body, liver, kidneys, gills, heart, and white muscle were determined every 2 to 4 weeks. Significant (p 6lt; 0.05) mortality was observed in green sturgeon fed the highest SeMet diet after 2 weeks, whereas no mortality was observed in white sturgeon. Growth rates were significantly reduced in both species; however, green sturgeon was more adversely affected by the treatment. Dietary SeMet significantly affected whole body composition and most noticeably, in the decline of lipid contents in green sturgeon. Selenium accumulated significantly in all tissues relative to the control groups. After 4 and 8 weeks of exposure, marked abnormalities were observed in the kidneys and liver of both sturgeon species; however, green sturgeon was more susceptible to SeMet than white sturgeon at all dietary SeMet levels. Our results showed that a dietary Se concentration at 19.7 ± 0.6 mg Se/kg, which is in range with the reported Se concentrations of the benthic macro-vertebrate community of the San Francisco Bay, had adverse effects on both sturgeon species. However, the exposure had a more severe pathological effect on green sturgeon, suggesting that when implementing conservation measures, this federally listed threatened species should be monitored and managed independently from white sturgeon

Effects of dietary methylmercury on growth performance and tissue burden in juvenile green (<i>Acipenser medirostris</i>) and white sturgeon (<i>A. transmontanus</i>)

Triplicate groups of juvenile green and white sturgeon (30 ± 2 g) were exposed to one of the four nominal concentrations of dietary methylmercury (MeHg, 0 (control), 25, 50, and 100 mg MeHg/kg diet) for 8 weeks to determine and compare the effects on growth performance and mercury (Hg) tissue burden in the two sturgeon species. Mortality, growth performance as measured by percent body weight increase per day, hepatosomatic index, proximate composition of whole body, and Hg burden in the whole body, gill, heart, liver, kidney, and white muscle were determined to assess the adverse growth effects and bioaccumulation of dietary MeHg in sturgeon. Significantly higher mortality and lower growth rate (p &lt; 0.05) were noted in green and white sturgeon fed the MeHg diets compared to the controls. Green sturgeon fed the MeHg diets exhibited earlier and more severe adverse effects compared to white sturgeon. Mercury accumulated in all tissues in a dose-dependent manner regardless of species, and the highest Hg concentrations were found in the kidneys of both species. Dietary MeHg had no significant effect (p &gt; 0.05) on the whole body proximate compositions of either sturgeon species. In conclusion, green sturgeon was more susceptible to dietary MeHg toxicity than white sturgeon in our 8-week growth experiment based on the higher mortality and lower growth rate and body energy contents

Effects of feeding rates on growth performances of white sturgeon (<i>Acipenser transmontanus</i>) fries

Four 1-week growth trials were conducted to determine the effects of feeding rates on the growth performances of white sturgeon (Acipenser transmontanus) fries 6–9 weeks after initiation of feeding. Six feeding rates with four replications were used in each of the four trials, and the feeding rates were 3.0–8.0, 2.0–7.0, 1.0–6.0 and 1.0–6.0% body weight (BW) per day in 1% increment, respectively. Number of fries per replicate and their initial BW (means ± SEM) were 60, 45, 30 and 30 and 2.8 ± 0.1, 4.5 ± 0.4, 8.5 ± 0.7 and 10.0 ± 0.7 g, respectively. The fries were kept at 18–19 °C and fed a commercial salmonid feed (488 g kg−1 protein and 123 g kg−1 fat). Mortality was low and unrelated to feeding rates. Final body weights, body weight increases, specific growth rates and feed efficiency were significantly (P &lt; 0.05) affected by the feeding rates. Body moisture and lipid contents were significantly affected by feeding rates except body moisture content in trial II. Body protein contents were not affected by feeding rates except in trial III. Broken-line analysis on specific growth rates indicated that the optimum feeding rates were 6.5 ± 0.4, 4.8 ± 0.2, 4.2 ± 0.1 and 3.8 ± 0.2% body weight per day, respectively, for white sturgeon fries 6–9 weeks after initiation of feeding