Fish, developmental effects

Figure 7 shows the effect of ectopic administration of T3 to the developing zebrafish embryo. At nontoxic concentration (50 nM), only a moderate fraction (less than 5%) of the zebrafish transcriptome shows significant changes. Ossification, visual processes, and the hematopoietic system were the physiological processes most affected by the treatment, in a pattern consistent with an advancement of the development in these particular functions (Fig. 7b). Genes involved in these three processes are known targets for TDCs during metamorphosis in amphibians, teleost fishes, and lampreys [54—60], and constitute molecular counterparts of different endpoints used to test for TDC in amphibians [56, 58]. Therefore, they are excellent candidates for markers of thyroid disruptors in zebrafish at early developmental stages. Chapter 14 provides a more in-deep description of the developmental effects of thyroid disruption in zebrafish embryos.

In the late 1950s the subtle and serious consequences of methyl mercury exposure became evident in Minamata, Japan. Initially, early signs of uncoordinated movement and numbness around the lips and extremities, followed by constriction in visual fields in fishermen and their families, baffled health experts. Developmental effects were clearly evident in infants who exhibited subtle to severe disabilities. This spectrum of adverse effects was finally related to methyl mercury exposure from consumption of contaminated fish. Minamata Bay was contaminated with mercury and methyl mercury from a factory manufacturing the chemical acetaldehyde. Mercury was used in the manufacturing process, which also resulted in both mercury and methyl mercury being discharged into Minamata Bay. The fish in the bay accu-... 

The primary human exposure to methyl mercury is from consumption of contaminated fish. The most sensitive population is the developing fetus or infant due to the effects of methyl mercury on the nervous system (neurotoxic) and developmental effects. Exposure limits and fish consumption advisories are directed at pregnant women, women of childbearing age, and children. All agencies also recognize that fish consumption has many nutritional benefits and is an important part of many people s diet. Nevertheless, the widespread distribution of mercury and subsequent bioaccumulation of methyl mercury requires that many agencies have developed recommendation for levels of mercury in fish. Below is a list of some of these recommendations, but it is very important to consult the local fish consumption advisories. 

Mercury - organic (Hg-CH3) Tremor, developmental effects on nervous system Fish... 

Bacteria convert mercury (quick silver) to methyl mercury (CH3-Hg) in an effort to detoxify the mercury. Other organisms, including fish, consume the bacteria along with the methyl mercury. Larger fish consume the smaller fish and accumulate methyl mercury in muscle. Humans and other animals consume the fish and can be poisoned by the mercury. The developing fetus is particularly sensitive to the adverse developmental effects of methyl mercury. The tragic effects of fetal methyl mercury... 

Fish partial and full life-cycle test methods have been used successfully for many years to assess the effects of nonendocrine active chemicals (McKim 1977) and more recently to focus on high-priority endocrine disrupters (Tyler et al. 1998 Huet 2000 Lange et al. 2001). In some cases, there may also be a need to measure the potential for chronic effects on amphibians, for which developmental effect test methods are available (Devillers and Exbrayat 1992 Pickford et al. 2003). Again, in line with current knowledge, PNEC assessments should be based on impaired fitness parameters (e.g., reduced rates of fertility, development, or fecundity) and not on molecular or biochemical changes (see Figure 4.3). 

Methylmercury is the form of mercury most commonly associated with a risk for developmental effects. Exposure can come from foods contaminated with mercury on the surface (for example, from seed grain treated with methylmercury to kill fungus) or from foods that contain toxic levels of methylmercury (as in some fish, wild game, and marine mammals). Mothers who are exposed to methylmercury and breast-feed their infant may also expose the child through the milk. The... 

There are differences in the outcomes of these epidemiology studies on low level chronic exposures to methylmercury in foods. Davidson et al. (1998) report no adverse developmental effects associated with prenatal and postnatal exposure to methylmercury in fish in a Seychelles Island cohort of children at age 66 months (n=708). The exposure levels are reflected in maternal hair levels of 6.8 ppm for the prenatal exposure (SD=4.5, n=711) and children s hair levels of 6.5 ppm (SD=3.3, n=708) for both the prenatal and subsequent postnatal exposure. The age-appropriate main outcome measures included (1) the... 

Monosson, E. Reproductive and developmental effects of PCBs in fish a synthesis of laboratory and field studies. Rev. Toxicol. 3 25-75, 2000. 

Schantz, SL University of Illinois Urbana Developmental effects of fish-borne toxicants in rats USDA or cooperating state institutions... 

Seegal, Richard F Wadsworth Center, Albany, NY Developmental effects of fish borne toxicants in the rat NIEHS... 

A number of studies have summarized potential impacts to different types of organisms, including adult fish, developmental fish, zooplankton, and benthic fauna. While earlier studies focused mainly on lethal impacts to coastal fauna exposed to strong acids, recent data have focused on deep-water organisms exposed to CO2, and have included sub-lethal effects. Impacts include respiratory stress (reduced pH limits oxygen binding and transport of respiratory proteins), acidosis (reduced pH disrupts an organism s acid/basis balance), and metabolic depression (elevated CO2 causes some animals to reach a state of torpor). 

Several trends are evident from Table 9.6 (1) freshwater fishes are more sensitive to zinc than marine species (2) embryos and larvae are the most sensitive developmental stages (3) lethal and sublethal effects occur in the range 50 to 235 pg Zn/L for most species, and 4.9 to 9.8 pg Zn/L for brown trout (Salmo trutta) and (4) behavioral modifications, such as avoidance, occur at concentrations as low as 5.6 pg Zn/L. 

Reproductive impairment seems to be one of the more sensitive indicators of zinc stress in freshwater teleosts, with effects evident in the range 50 to 340 pg Zn/L (Spear 1981). In some cases, reproduction was almost totally inhibited at zinc concentrations that had no effect on survival, growth, or maturation of these same fish (Brungs 1969). Zinc-induced developmental abnormalities were documented in marine teleosts, but concentrations tested were grossly elevated. Eggs of the Baltic herring (Clupea harengus), for example, exposed to >6 mg Zn/L have an altered rate of development and produce deformed larvae with cellular disruptions in the brain, muscle, and epidermis (Somasundaram 1985 Somasundaram et al. 1985). 

---