Evaluation of water quality during successive severe drought years within Microcystis blooms using fish embryo toxicity tests for the San Francisco Estuary, California.

In the San Francisco Estuary, California, the largest estuary on the Pacific Coast of North America, the frequency and intensity of drought and associated cyanobacteria blooms are predicted to increase with climate change. To assess the impact of water quality conditions on estuarine fish health during successive severe drought years with Microcystis blooms, we performed fish embryo toxicity testing with Delta Smelt and Medaka. Fish embryos were exposed to filtered ambient water collected from the San Francisco Estuary during the Microcystis bloom season in 2014 and 2015, the third and fourth most severe recorded drought years in California. Medaka embryos incubated in filtered ambient waters exhibited high mortality rates (>77%), which was mainly due to bacterial growth. Medaka mortality data was negatively correlated with chloride, and positively correlated with water temperature, total and dissolved organic carbon, and ambient and net chlorophyll a concentration. Delta Smelt embryo mortality rates were lower (<42%) and no prominent seasonal or geographic trend was observed. There was no significant correlation between the Delta Smelt mortality data and water quality parameters. Aeromonas was the dominant bacteria that adversely affected Medaka. The growth of Aeromonas was suppressed when salinity was greater than or equal to 1psu and resulted in a significant reduction in mortality rate. Bacterial growth test demonstrated that the lysate of Microcystis cells enhanced the growth of Aeromonas. Toxin production by Microcystis is a major environmental concern, however, we conclude that dissolved substances released from Microcystis blooms could result in water quality deterioration by promoting growth of bacteria. Furthermore, a distinctive developmental deformity was observed in Medaka during the toxicity tests; somite formation was inhibited at the same time that cardiogenesis occurred and the functional heart was observed to be beating. The exact cause of the embryonic developmental deformity is still unknown.

Effects of 17ß-estradiol and 17α-ethinylestradiol on the embryonic development of the clearhead icefish (Protosalanx hyalocranius).

Estrogenic effects of 17ß-estradiol (E2) and 17α-ethinylestradiol (EE2) on animals have been widely reported. The high sensitivity of fish in the early-life stages to xenobiotics can be exploited to evaluate the developmental effects of environmentally relevant levels of E2 and EE2. In this work, clearhead icefish (Protosalanx hyalocranius) embryos (blastula stage) were exposed to E2 or EE2 at concentrations between 0.05 ng/L and 1 mg/L. The toxicity endpoints of mortality, teratogenesis, and hatching retardation were evaluated. The results showed that continuous exposure of the fish embryos/larvae to higher concentrations of E2 and EE2 dramatically increased mortality after 17 days, when the hatching period started. An E2 concentration of 8 µg/L (day 16) and an EE2 concentration of at 0.2 mg/L (day 18) induced maximum teratogenesis rates of 30% and 35%, respectively. Embryos exposed to 0.2 mg E2 or EE2/L had a significantly retarded hatching time compared to the control. Thus, although environmentally relevant concentrations E2 and EE2 are not lethal for P. hyalocranius embryos or larvae, their ability to induce teratogenesis and hatching retardation merits concern.

Integrating multiple bioassays to detect and assess impacts of sublethal exposure to metal mixtures in an estuarine fish.

Estuaries are natural sinks for a wide range of urban, industrial and agricultural contaminants that accumulate at potentially toxic but non-lethal concentrations, yet we know relatively little about the long-term impacts of toxicants at these levels on aquatic organisms. In this study, we present an integrated, multi-pronged approach to detect and assess the impacts to estuarine fish of exposure to sublethal concentrations of metal mixtures. Our aims were to (1) examine the effects of sublethal metal exposure on the embryonic development of Galaxias maculatus, an estuarine spawning fish native to southeastern Australia, (2) determine whether sublethal exposure during development has knock-on effects on larval behaviour, and (3) establish whether a signature of metal exposure during embryogenesis can be detected in larval otoliths ("ear bones"). G. maculatus eggs are fertilised in water but develop aerially, in direct contact with estuarine sediments. We were thus also able to explore the relative importance of two exposure pathways, water and sediment. Embryos were exposed to two concentrations of a metal mixture containing Cu, Zn and Pb in water (during fertilisation) and on spiked sediments (during development), using a fully crossed experimental design. Overall, we found that exposure to the metal mixture reduced embryo survival and slowed embryonic development, resulting in poorer quality larvae that exhibited a reduced phototactic response. Differences in exposure to metals between treatment and control embryos were also permanently recorded in the developing otoliths. Combined these three approaches have the potential to be a powerful novel bioassessment tool as they provide a means of identifying a history of metal exposure during the embryonic period and linking it to suboptimal early growth and performance traits which could have long term fitness consequences.

Cloning the Dmrt1 and DmrtA2 genes of ayu (Plecoglossus altivelis) and mapping their expression in adult, larval, and embryonic stages.

The Dmrt family of genes are involved in sex differentiation in different species of invertebrates, and some vertebrates including human. In this study, we cloned the full-length cDNA of ayu (Plecoglossus altivelis) Dmrt1 and DmrtA2. Sequence and phylogenetic tree analyses showed ayu Dmrt1 showed highest similarity to that of Oncorhynchus mykiss while ayu DmrtA2 is most similar to that of Oryzias latipes. Fluorescence-based quantitative reverse transcription PCR (qRT-PCR) revealed the Dmrt1 was predominantly expressed in the testis. At the larval stages, Dmrt1 mRNA expression level was highest during 52-64 days post hatching (dph) and at the gastrula stage during embryonic development. DmrtA2, meanwhile, was specifically expressed in the ovary and was highly expressed in the female brain tissue, but not male brain tissue. During the larval stages, DmrtA2 expression remained high before day 34, and then fluctuated while generally decreasing. During embryonic development, DmrtA2 expression increased gradually and peaked at the hatching stage. Our data suggest that ayu Dmrt1 might participate in the differentiation and maintenance of testis while DmrtA2 may play a role in ovary-differentiation and mature-ovary maintenance. DmrtA2 might also participate in brain development.

Toxicity of crude oil and pyrene to the embryos of beach spawning capelin (Mallotus villosus).

Due to a northward shift in oil and gas activities, there is an increasing need to understand the potential anthropogenic impacts of oil-related compounds on sub-Arctic and Arctic organisms, particularly those in coastal habitats. Capelin (Mallotus villosus), a key fish species in the Barents Sea ecosystem, undertakes aggregated spawning at both intertidal and subtidal coastal localities in northern Norway. To investigate the sensitivity of capelin embryos to oil compounds, newly fertilized capelin eggs were collected from a spawning beach and exposed until hatch (32 days) to either the water soluble fraction of crude oil or the single PAH compound, pyrene. Threshold levels for egg mortality, development and hatching success were determined. Concentrations of 40 µg/L crude oil (∑26 PAHs) and 55 µg/L pyrene significantly increased embryonic mortality rates and decreased hatching success, compared with controls, indicating that a potential oil spill in the vicinity of capelin spawning grounds may cause significant impacts. No significant incidence of adverse effects such as yolk sac oedema, pericardia oedema, haemorrhages, craniofacial abnormalities, premature hatch or inhibited growth was observed. Histological studies of hatched larvae did not reveal specific sublethal effects in tissues and organs. Developmental delays and subsequent embryo death were noticed at the period of eye pigmentation in affected groups. Early life-history stages of capelin are sensitive indicators of PAH impacts, but the mechanisms responsible for the toxic effects require further investigation.