Edmundo Casillas

Effect of Pollution on Fish Diseases: Potential Impacts on Salmonid Populations

Abstract Anthropogenic factors have contributed to the precipitous decline of wild Pacific salmon stocks, although the mechanisms and processes at work are largely unknown. Pollution may be one of these factors. Sediments in estuaries are known to act as repositories for contaminants, and estuaries are important habitats for ocean- and river-migrating salmon. We have shown that juvenile salmon Oncorhynchus spp. and their prey bioaccumulate chlorinated hydrocarbons and aromatic hydrocarbons—important classes of toxic xenobiotics. Furthermore, we have shown that exposure to these pollutants can lead to immunosuppression and increased disease susceptibility in juvenile salmon. Whether pollution influences natural disease outbreaks in host populations, including salmon, is currently unknown. It is postulated that the occurrence of disease depends on the interaction of the host, the environment, and the pathogen. Absence of pathogens would reduce the potential for adverse environments to influence disease outb...

Relationship of serum chemistry values to liver and kidney histopathology in English sole (Parophrys vetulus) after acute exposure to carbon tetrachloride

Abstract Carbon tetrachloride (CCl4) was injected intraperitoneally into English sole (Parophrys vetulus) to determine relationships between induced lesions of liver and kidney tissue and serum indicators of tissue damage. The CCl4 doses used were from 4 to 63% of the 96-h LC50 (4.8 ml CCl4/kg). Within 48 h post injection, histopathological changes in liver ranged from subcapsular hepatocellular coagulation necrosis with sinusoidal congestion to coagulation necrosis of centrally located hepatocytes and hepatocellular fatty change. Kidney lesions were minor at low doses of CCl4 but at higher doses pyknosis, microvacuolar degeneration, scalloping of the brush border and frank necrosis of the tubular epithelium in the second proximal kidney tubule were seen. Serum alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) activities were correlated with specific liver lesions. In addition, serum glucose was elevated 8 h after CCl4 injection, whereas serum albumin, total protein, bilirubin and urea nitrogen did not significantly change in relation to liver lesions after CCl4 exposure. Serum phosphate was found to be elevated in fish with kidney lesions. Serum creatinine, magnesium and calcium also reflected kidney damage, but only at the higher CCl4 concentrations. These studies suggest that some, but not all, of the classically used serum chemical indices of damage in liver and kidney tissue have diagnostic and prognostic utility for this species of marine fish.

Genetic and otolith isotopic markers identify salmon populations in the Columbia River at broad and fine geographic scales

Processes occurring in freshwater, estuarine, and marine habitats strongly influence the growth, survival and reproductive success of salmonids. Nonetheless, implementing an ecosystem model explicitly linking these important habitats has been hindered by the inability to track the source identity of individuals where they co-occur. Here we explore the development and integration of natural markers- molecular and isotopic to characterize the natal sources of Chinook salmon (Oncorhynchus tshawytscha) in the Mid and Upper Columbia River summer/fall-run (UCR Su/F) population. Microsatellite DNA markers identified the majority of juveniles collected in rivers and hatcheries in the Mid and Upper Columbia River watershed to the Summer/Fall-run population in this watershed with 90% posterior probabilities of group membership. Strontium isotopes (87Sr/86Sr) measured in the natal rearing portion of the otolith showed significant geographic variation among natal rivers and hatcheries. Natal sites exhibited a wide dynamic range in 87Sr/86Sr source signatures (0.7043–0.7142), such that on average 61% of individuals were correctly classified to the location from which they were collected. We found that multilocus genotypes and otolith 87Sr/86Sr ratios collected on the same individuals were complementary markers when applied in a hierarchy. Microsatellites successfully assigned individuals to the broader UCR Su/F genetic group and 87Sr/86Sr provided finer-scale geographic assignments to five natal river and hatchery groups nested within the UCR Su/F population. The temporal stability of both genetic and 87Sr/86Sr markers, together with the coast-wide microsatellite baseline currently being used for mixed-stock fisheries management supports the further development and integration of 87Sr/86Sr markers to potentially achieve finer levels of stock resolution. Stock identification at the scales of individual rivers and hatcheries would help elucidate the abundance, distribution, and the relative contributions of natal sources important for the recovery and spatial management of Chinook salmon.

Simultaneous exposure of English sole (Parophrys vetulus) to sediment-associated xenobiotics: Part 2—chronic exposure to an urban estuarine sediment with added 3H-benzo[a]pyrene and 14C-polychlorinated biphenyls☆

Abstract 1. 1. The accumulation of aromatic hydrocarbons (AHs) and polychlorinated biphenyls (PCBs) kv English sole (Parophrys vetulus) exposed for up to 108 days to an urban (test) sediment was compared to that for English sole exposed to sediment from a reference area. The concentrations of identified AHs and PCBs in the test sediment were 32 μg/g dry weight and 2·2 μg/g dry weight, respectively. English sole exposed to test and reference sediments for 108 days had biliary concentrations of aromatic compounds fluorescing at BaP wavelengths of 0·6 μg/g, wet weight and hepatic concentrations of PCBs of 1·4 ± 0·6 μg/g wet weight which were ten and eight times, respectively, as great as those in reference sole. These results show that accumulation of AHs and PCBs from sediment by English sole is a significant route of uptake in contaminated environments. 2. 2. 3H-benzo(a)pyrene (BaP) and 14C-PCBs were added to the test sediment to compare the uptake and metabolism of BaP to that of PCBs by sole. Steady-state concentrations of 3H-BaP and 14C-PCBs in tissues and fluids were reached by 4 days and 14 days, respectively. At steady state, the level of covalent binding of 3H-BaP to hepatic proteins in test sole was six times greater than that of 14C-PCBs, and there was significantly greater relative formation of BaP-glutathione (GSH) conjugates than PCB-GSH conjugates. Thus, the amount of BaP metabolized to reactive metabolites was greater than that for PCBs, even though the concentration of 14C-PCBs in liver of test sole was five times as great as that of 3H-BaP. 3. 3. Trace amounts of 3H-BaP were also added to the reference sediment to determine how simultaneous exposure of English sole to those contaminants already present in the test sediment affected the metabolism and disposition of BaP. The 3H-BaP concentration ratios for liver to sediment and bile to sediment, as well as proportions of biliary BaP-GSH conjugates in test sole, were significantly greater than in reference sole. Thus, the formation and accumulation of potentially toxic metabolites of a carcinogenic AH (BaP) in sole liver were increased by simultaneous exposure to contaminants present in an urban sediment.

Patterns of oocyte development and related changes in plasma 17-β estradiol, vitellogenin, and plasma chemistry in English sole Parophrys vetulus Girard

Abstract Ovarian development was monitored in female English sole Parophrys vetulus Girard from three sites in Puget Sound: Sinclair Inlet and Port Susan, where fish are normally resident, and University Point, a known spawning area for English sole. Histological changes in ovary and liver as well as changes in plasma estradiol and vitellogenin levels, gonadosomatic index, hepatosomatic index, and calcium, phosphate, magnesium, glucose, triglyceridesm total protein, and albumin concentrations in the plasma over the reproductive cycle were assessed. Vitellogenesis in female English sole began in the early fall, and swapping activity reached its peak in February. Oocyte development was group synchronous with two distinct clutches of oocytes in the maturing ovary. In general, the cytological and physiological changes which English sole underwent during the reproductive cycle were similar to those observed in other teleost species. However, certain distinctive features were observed, including a high prevalence of atresia of nonyolked oocytes.

Survey of Pathogens in Juvenile Salmon Oncorhynchus Spp. Migrating through Pacific Northwest Estuaries

Abstract Although the adverse impact of pathogens on salmon populations in the Pacific Northwest is often discussed and recognized, little is currently known regarding the incidence and corresponding significance of delayed disease-induced mortalities. In the study reported herein, we surveyed the presence and prevalence of selected micro- and macroparasites in out-migrant juvenile coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha from 12 coastal estuaries in the Pacific Northwest over a 6-year period (1996–2001). The major finding of this study was the widespread occurrence of pathogens in wild salmon from Pacific Northwest estuaries. The six most prevalent pathogens infecting both juvenile Chinook and coho salmon were Renibacterium salmoninarum, Nanophyetus salmincola, an erythrocytic cytoplasmic virus (erythrocytic inclusion body syndrome or erythrocytic necrosis virus), and three gram-negative bacteria (Listonella anguillarum, Yersinia ruckeri, and Aeromonas salmonicida). The most pre...

Contaminant effects on reproductive success in selected benthic fish

Abstract Field studies on ovarian development in English sole from urban and nonurban sites in Puget Sound, Washington, USA, demonstrated that animals with elevated levels of fluorescent aromatic compounds (FACs) in bile were less likely to enter vitellogenesis and had lower plasma concentrations of estradiol than female sole with low levels of contaminant exposure. Biliary FACs were positively correlated with hepatic P450 activity, which was also elevated in sole showing inhibited ovarian development. These findings suggest that contaminant exposure may disrupt vitellogenesis in female fish. Results of the field study were supported by laboratory experiments showing that pretreatment of gravid female English sole with extracts of contaminated sediment decreased levels of endogenous estradiol. A similar response was observed in rock sole and flathead sole treated with Prudhoe Bay crude oil. However, exposure of English sole to sediment extracts had little effect on the activity of hepatic-steroid-metabolizing enzymes, indicating that some mechanism other than enhanced steroid metabolism may be responsible for reductions in endogenous circulating-steroid levels. Our recent studies suggest that reductions in endogenous estradiol levels may result from depressed ovarian steroidogenesis, as contaminant-associated reductions in in-vitro ovarian estradiol production were observed in English sole, rock sole, and flathead sole. Preliminary studies on winter flounder and white croaker indicate that they may also experience reproductive impairment as a result of exposure to contaminants, but the phase of the reproductive cycle that is most severely impacted varies from species to species.

Hepatotoxic effects of CCl4, on English sole (Parophrys vetulus): possible indicators of liver dysfunction

Selected serum parameters (enzyme activities and triglycerides) and liver glutathione and vitamin C concentrations were measured in English sole (Parophrys vetulus) after i.p. injection of carbon tetrachloride (CCl4), a hepatotoxin in fish. Serum lactate dehydrogenase (LDH), alkaline phosphatase (AP) and glutamate dehydrogenase (GDH) activities and the concentration of triglycerides increased in a dose-dependent manner 24 hr post injection. Concentrations of glutathione (reduced and oxidized) and ascorbic acid (vitamin C) in liver did not change in response to CCl4 toxicity 24 hr post injection. These studies indicate that serum AP activity and triglyceride concentrations can be useful in assessing the effects of CCl4-induced liver toxicity in this species of marine fish. Serum LDH and GDH activity should be used with some caution in assessing liver damage in English sole, as other tissues represent more likely sources for serum activity. The levels of liver antioxidants do not appear to be significantly affected, 24 hr post injection, by this particular hepatotoxin.

Indicators of reproductive development in prespawning female winter flounder (Pleuronectes americanus) from urban and non-urban estuaries in the northeast United States

The relationship between exposure to xenobiotic compounds and ovarian development was evaluated in prespawning female winter flounder (Pleuronectes americanus) sampled from eleven sites on the northeast coast of the United States during the 1988 and 1989 spawning seasons. Three sites were located in Boston Harbor, MA, four sites were in Raritan Bay, NJ and four sites were in nearby embayments. Sediments from these sites exhibited a wide range in concentrations of xenobiotic compounds (e.g. aromatic hydrocarbon (PAH) concentrations ranged from 20 to 50 000 ng/g dry wt. and polychlorinated biphenyl (PCB) concentrations ranged from 2 to 1400 ng/g dry wt.), with the sites in Boston Harbor and Raritan Bay the most heavily contaminated. The following parameters associated with ovarian development were measured: ovarian developmental stage, ovarian atresia, gonadosomatic index, plasma estradiol, fecundity and egg weight. Contaminant exposure was assessed by measuring concentrations of fluorescent aromatic compounds (FACs) in the bile, hepatic aryl hydrocarbon hydroxylase (AHH) activity, concentrations of PCB in liver, ovary and brain and concentrations of xenobiotic-DNA adducts in liver tissue. Additionally, liver tissue was examined histologically for the presence of suspected toxicopathic lesions. In general, indicators of contaminant exposure were elevated and prevalences of suspected toxicopathic lesions were highest in fish from sites within Boston Harbor and Raritan Bay. Hepatic AHH activity, however, was heavily influenced by the reproductive cycle and showed little correlation with other indicators of contaminant exposure. Evidence of decreased egg weight and increased atresia in fish with high tissue concentrations of PCB or high levels of FACs in bile was observed. However, contaminant exposure had no clear negative impact on gonadal recrudescence, gonadosomatic index, plasma estradiol concentrations, or fecundity in female winter flounder. These results are in contrast to results with another Pleuronectid species, English sole (Pleuronectes vetulus), which shows inhibited gonadal development and lower plasma estradiol concentrations at contaminated sites in Puget Sound, WA. The apparent difference between English sole and winter flounder in susceptibility to contaminant-induced reproductive dysfunction could be related to a number of factors, including the differences in the migratory behavior of the two species during the reproductive season. English sole reside in contaminated estuaries throughout vitellogenesis and move offshore to spawn, while winter flounder often remain offshore for extended periods during early vitellogenesis and move into contaminated estuaries prior to spawning. Because of these contrasting migration patterns, both the duration and timing of exposure to contaminants during gonadal recrudescence may differ substantially in these two species and may contribute, in part, to the observed differences in the prevalence of reproductive dysfunction in fish from contaminated estuaries.

Effects of contaminated sediments on viability, length, DNA and protein content of larval surf smelt, Hypomesus pretiosus

Abstract Mortality, abnormal morphology, growth, DNA and protein content of larval surf smelt (Hypomesus pretiosus) were evaluated after 96-h exposures to contaminated sediments from Puget Sound, Washington. Radiolabeled polynuclear aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) added to sediment were accumulated by exposed larvae, providing evidence of an exposure route for hydrophobic compounds from the sediment to the larvae. Sediment mixtures with high concentrations of contaminants were often acutely toxic, while exposure to diluted sediments resulted in sublethal changes—decreases in growth and DNA content. The DNA content of larvae was found to be the most sensitive of the sublethal measures. Both DNA content and the proportion of normal larvae were inversely related to PAH and PCB concentrations of test sediments. The results suggest that measurement of DNA content in conjunction with determination of the proportion of normal larval surf smelt can provide better discrimination for assessing toxicity due to contaminants in this sediment bioassay system than measurement of mortality alone. Because some larval fish may be at risk to sediment-associated contaminants, this bioassay may be useful for assessing the effects on larval marine fishes exposed to contaminants.