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This study examined the responses of a population of brook stickleback (Culaea inconstans) exposed to pulp mill effluent at Jackfish Bay, Lake Superior, Canada, in May 2007 and May 2011. Brook stickleback were extirpated from the effluent-receiving site, presumably due to anoxia after this period. Females at the effluent-receiving site had significantly larger gonad sizes in 2007 and 2011. In 2011, effluent-exposed female gonadal development was significantly advanced when compared with reference sites; they were the second most mature when compared among three different reference sites. Analysis of 7-ethoxyresorufin-O-deethylase activity revealed that effluent-receiving site females had greater CYP1A induction in 2007 and significantly greater CYP1A induction in 2011. Effluent-receiving site males showed significantly reduced CYP1A induction in 2007 and significantly greater induction in 2011. Chemical evaluation of sediment from the receiving environment showed elevated levels of resin acids and the polycyclic aromatic hydrocarbon, retene. Higher condition factors and more mature gonads were consistent with higher winter and spring temperatures modified by effluent or by lake vs. stream environments. Overall, effects on effluent-exposed brook stickleback were not consistent with reported effects in white sucker exposed to the same effluent in previous studies. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).

Reproductive impairment in fishes exposed to pulp and paper effluent has been observed in the wild for three decades. Despite intense research, identification of causative agents, if indeed the changes are strictly chemically mediated, has yet to be achieved. This review examines the body of research developed over the last six years that was directed at understanding the mechanisms of reproductive dysfunction in fishes associated with pulp mill effluent exposures. Research has continued to show diminishing effects of effluent exposure on fish reproductive physiology. Observations of exposure to androgens and estrogens continue to be observed and new evidence suggests that antiestrogens may be present. The presence of androgenic steroids remains a consistent observation, and those androgens appear to be native to wood. Recent studies have also suggested a number of alternate mechanisms beyond androgens or estrogens. One such possibility is that neuroactive substances are interfering with endocrine balance critical to reproduction. A second possibility is that some reproductive effects in the field may be due to nutritional factors, and thus reproductive impacts are caused by indirect effects of pulp mill effluent exposure. Ongoing mechanistic studies, particularly with paired field-lab components, are required to make further progress.

The effluent of the Tasman pulp and paper mill (Kawerau, New Zealand) has been intensively studied for its effects on the health of fishes between 1998 and present. This review summarizes peer-reviewed scientific literature on the reproductive effects of the Tasman Mill effluent on fishes. In the 1990s there was an emerging body of literature from around the world showing that exposure to pulp and paper effluent could cause subtle reproductive alterations in exposed fishes. Locally, the Tarawera River had proved to be a difficult environment to conduct field studies. To overcome some of the difficulties with studying fish populations in the Tarawera River, initial studies on the reproductive health of fishes were focused on mesocosm and laboratory bioassays. During the later part of this period of study, wild fish population sampling was conducted inriver to assess the cumulative impact of multiple discharges. The initial mesocosm studies were conducted with rainbow trout exposures over an entire reproductive development cycle. The Tasman Mill effluent was initially observed to cause reductions in gonad size in females corresponding with lower circulating sex steroid hormones and reduced egg and larval sizes. This result was not observed again in the two subsequent long-term exposures conducted after 2001. Laboratory studies initially found the effluent to have a masculinizing effect on female mosquitofish (Gambusia affinis). This mosquitofish masculinization response disappeared after 2001 and was also not seen in effluent-exposed wild populations. Upstream and downstream populations of the native common bully (Gobiomorphus cotidianus) showed different reproductive timing, and investigation revealed that genetic differences were a potential reason for these differences. Subsequent investigation compared the Tarawera River bully to genetically similar Rangitiki River bully and found no evidence of reproductive alterations. The entire body of published data was assessed with regards to changes at the mill and chemical profiles of the effluent. It was evident that continuing effort on the part of the mill has resulted in gradual improvement in effluent quality over the duration of the studies. However, the disappearance of reproductive effects as assessed by multiple bioassays corresponds to one major change: screen room closure in the pulp mill. This change would have resulted in wood extractives being shunted from the treatment system to the recovery boiler, resulting in a net reduction in compounds derived from wood.

To evaluate currently available bioassays for their use in investigating the causes of pulp and paper mill effluent effects on fish reproduction, the responses of wild white sucker (Catostomus commersoni) collected from the receiving environment at the bleached kraft mill at La Tuque, Quebec, were compared with responses of fathead minnow (Pimephales promelas) exposed to effluent in a laboratory lifecycle test. White sucker collected at effluent exposed sites had increased liver size but none of the reproductive effects that had been documented in earlier field studies at this site. Exposure to 1, 3, 10, 30, and 100% bleached kraft mill effluent (BKME) in the lab led to significantly decreased length, but increased weight and liver size in male fathead minnow. Female length was also decreased and liver size was increased at high effluent exposures. Most effluent concentrations (1 to 30%) significantly increased egg production compared with controls. The fathead minnow lifecycle assay mirrored the effects seen in wild fish captured downstream of the BKME discharge. These results will be used to select short-term fish tests for investigating the causes of and solutions to the effects of mill effluents on fish reproduction.

This study examined the comparative physiological health of the endemic New Zealand common bully (Gobiomorphus cotidianus) in the Tarawera and Rangitaiki Rivers. Bully were sampled downstream of pulp and paper effluent inputs in the Tarawera River and compared with a similar inland population in the Rangitaiki River. Condition factor and liver somatic index did not differ between populations, but Tarawera River bullies possessed larger gonads. Haematological assessments found smaller erythrocytes with reduced haemoglobin content, and increased leukocyte concentrations in Tarawera River females. Male and female Tarawera River bullies had significantly induced hepatic ethoxyresorufin-O-deethylase (EROD) activity. Greater ovarian follicular steroid production was also found for Tarawera River females. Microscopic analysis of ovarian tissue samples found no histopathological abnormalities in either population and indicated a slightly advanced vitellogenic stage of development in the Tarawera River population. It is concluded that the difference in steroid production between populations was most likely linked to gonad size and developmental status. In line with the disappearance of physiological effects in recent controlled laboratory and mesocosm pulp and paper effluent exposures, this study further demonstrates that, with the exception of EROD induction, characteristic pulp and paper effluent effects are not obvious in wild Tarawera fish.

Under the Canadian Environmental Effects Monitoring (EEM) program for pulp and paper effluents, the observation of a national response pattern of decreased gonad size and increased fish condition and liver size has triggered a centralized multiagency investigation of cause (IOC) of reproductive impacts in fishes. The purpose of the component of the IOC study presented here is to compare a number of fish bioassays for determining reproductive and reproductive-endocrine effects of a bleached kraft mill effluent. The bleached kraft mill chosen for this study had demonstrated the national response pattern in previous EEM cycles. The bioassays employed to examine reproduction were fathead minnow (Pimephales promelas) 5- and 21-d, mummichog (Fundulus heteroclitus) 25-d, and zebrafish (Danio rerio) 7-d tests, all of which had egg production as the primary reproductive endpoint. Additional bioassays examining reproductive-endocrine endpoints included a 7-d mummichog test, a 7- and a 21-d threespine stickleback (Gasterosteus aculeatus) test, a rainbow trout (Oncorhynchus mykiss) 7-d test, and in vitro sex steroid receptor and plasma protein binding bioassays. The zebrafish and fathead minnow reproductive tests showed significant suppression of egg production at the 100% effluent concentration. Endocrine data derived from the tests showed that this effluent did not impact steroidogenic endpoints at any concentration. Bioassays showed that this effluent i) was capable of eliciting cytochrome P4501A induction at as low as 10% vol/vol effluent, ii) was weakly androgenic at 10% vol/vol, and iii) showed no evidence of in vivo estrogenicity. These results were consistent with in vitro receptor binding assays showing a highly variable level of androgenic equivalents over six months of effluent testing, with little evidence of estrogenic activity. Bioassay results were consistent in that the overall conclusion was that this effluent has only a weak potential to cause reproductive impairment and would likely not do so at environmentally relevant concentrations. Field studies and a fathead minnow lifecycle study conducted concurrently were in agreement with reproductive bioassay results as white sucker exposed in the receiving environment no longer had significantly reduced gonadal development. Overall, this study provided evidence that the laboratory assays evaluated for various reproductive endpoints have potential application for future IOC work.

The use of multiple spawning fishes in environmental effects monitoring programs has proven difficult for a number of reasons including the inability to predict reproductive investment and ensure synchronous sampling of reference and impacted populations. The estuarine resident northern mummichog (Fundulus heteroclitus macrolepidotus) has been successfully used as a sentinel for effects of pulp and paper mill effluents in Atlantic Canada and has been proposed for monitoring other anthropogenic impacts. This study investigated the spatial and temporal variability of the somatic parameters used to describe fish performance, specifically measures of energy use and storage, in estuaries located in Prince Edward Island, Canada. Three sites with varying levels of agricultural input were studied. Fish at all sites depleted their energy reserves over winter, as reflected in depressed condition, liver size, and gonad size, but then quickly replenished them in May. These population parameters were highly variable throughout the reproductive season and within an estuary. Spawning was continuous at all sites without indication of lunar or other periodicity. We conclude that repeated sampling is required to assess reproductive output in the northern mummichog and densities of adults and young-of-the-year deserve further investigation as a potentially less logistically demanding indicator of eutrophication.