Aquaculture has been the fastest-growing food production sector during the last decades. The supply–demand gap for fish is constantly widening, and declining freshwater availability is becoming a major limiting factor for production. Exploring alternative water resources, such as treated wastewater (TWW), has become a growing strategy for coping with the increasing water demand in agriculture. Reuse of wastewater or TWW for agriculture and aquaculture has been practiced around the world for centuries. However, the extent of the practice and the scientific attention paid to TWW reuse for aquaculture are negligible compared to those for agricultural irrigation. The objectives of this review are to present the existing literature on treated-wastewater-fed aquaculture, to evaluate the prospective reuse of TWW for aquaculture and its economic appraisal, and to identify the scientific and legislative gaps and challenges towards implementation. Most of the published studies on fish culture in TWW suggest that it is feasible in terms of fish survival and growth. Research also shows that fish are safe for human consumption in terms of microbiological contamination and the bioaccumulation of heavy metals and certain organic-micropollutants, with levels found to be in accordance with international standards for human consumption. Moreover, reuse of TWW as an alternative water source for aquaculture holds economic and environmental advantages. It appears that the sociocultural perception is a major barrier, which can be overcome by a combination of further research, legislation and public relations, which can support the implementation of TWW reuse for aquaculture.

Aquaculture in treated wastewater (TWW) has been practiced around the world, yet this field of research is backed with only scant scientific data, especially the aspect of the bioaccumulation of organic micropollutants (OMPs) in fish. The objectives of this study were to evaluate how fish culture in tertiary TWW (TTWW) affects commercially important traits, such as fish survival, growth rate and health, and to assess the potential risks associated with food safety and consumer protection. Cyprinus carpio juveniles were raised in 0%, 50% and 100% TTWW, for five months. Fish performance and health parameters were not affected by exposure to TTWW. The levels of heavy metals in the fish muscle were below the FAO and EU maximal permitted levels in edible fish. Seven out of 40 screened OMPs were detected in the TTWW samples at least once. Out of the 19 analyzed OMPs in fish tissues, four were detected in exposed fish. Carbamazepine and diclofenac were detected in the muscles and livers of fish grown in 50% and 100% TTWW at measurable concentrations. Carbamazepine-epoxide and diphenhydramine concentrations were below the limit of quantification (LOQ) in the muscle of the exposed fish, while diphenhydramine was detected above the LOQ level in two liver samples of fish grown in 100% TTWW. Based on the presented findings, TTWW can be successfully used for growing fish, and TTWW-grown fish met all the existing standards for heavy metals accumulation. However, the issue of OMP's bioaccumulation needs to be further studied in different fish species and culture conditions to broaden the perspective of the findings.

Treated wastewater (TWW) constitutes a sustainable water resource and has been used for fish culture in some countries around the world, although there are no comprehensive data on the effect of TWW on fish growth and health in the context of aquaculture production. Our objectives were to examine how fish culture in TWW affected fish growth and fitness, as well as compliance with the international standards for safe consumption. Guppy (Poecilia reticulata) fingerlings were reared in 0%, 50% and 100% tertiary TWW (TTWW), from the age of five days, for a period of four months. In water analyses, 33 out of 67 tested organic micropollutants (OMPs) were detected in the TTWW samples at least once, at concentrations that are typically reported in domestic TTWW. Fish survival ranged between 77-80% and did not differ between treatment groups. Fish growth and mortality following challenge infection with Tetrahymena sp. (which ranged between 64-68%), were similar among treatment groups. Of tested immunological parameters, lysozyme and anti-protease was similar among treatments while complement activity was highest in the 50% TTWW-reared fish. No abnormalities were observed in the histopathological analysis. Levels of heavy metals, polychlorinated-biphenyls (PCBs) and organochlorines (OCs) in fish were below the detection limit and below the Food and Agriculture Organization of the United Nations (FAO) and the European Union EU maximal permitted levels in food fish. Results suggest that the yield of fish grown in TTWW is potentially similar to that in freshwater, and the produced fish comply with the standards of consumer safety. The results are in line with previous studies that examined the feasibility of TWW-fed aquaculture.

Treated wastewater (TWW) reuse for agricultural irrigation is a well-established approach to coping with water shortages in semi-arid and arid environments. Recently, additional uses of TWW have emerged, including streamflow augmentation and aquatic ecosystem restoration. The purpose of the current study was to evaluate the water quality and fish health, in an artificial reservoir located in an arid climate (the Yeruham Reservoir, Israel), which regularly receives TWW and sporadic winter floods. The temporal distribution of water levels, nutrients and organic micropollutants (OMPs) were measured during the years 2013–2014. OMPs were also measured in sediment and fish tissues. Finally, the status of fish health was evaluated by histopathology. Water levels and quality were mainly influenced by seasonal processes such as floods and evaporation, and not by the discharge of TWW. Out of 16 tested OMPs, estrone, carbamazepine, diclofenac and bezafibrate were found in the reservoir water, but mostly at concentrations below the predicted no-effect concentration (PNEC) for fish. Concentrations of PCBs and dioxins in fish muscle and liver were much lower than the EU maximal permitted concentrations, and similar to concentrations that were found in food fish in Israel and Europe. In the histopathological analysis, there were no evident tissue abnormalities, and low to moderate infection levels of fish parasites were recorded. The results from the Yeruham Reservoir demonstrated a unique model for the mixture effect between TWW reuse and natural floods to support a unique stable and thriving ecosystem in a water reservoir located in an arid region. This type of reservoir can be widely used for recreation, education, and the social and economic development of a rural environment, such as has occurred in the Yeruham region.

The Asiatic Wild Ass, Equus hemionus, was once abundant in western Asia. The species declined due to hunting and habitat loss. Between 1982-93 38 E. hemionus (21♀ 17♂) were reintroduced to the Negev Desert, Israel. Saltz, Rubinstein and co-workers studied the released population till 1999. The current population in the Negev is estimated at more than 200 individuals, yet, their social structure is not known. Here we report group composition and behavior of E. hemionus near a water source. We recorded and videotaped in 2010 group composition and social interactions from a shelter, 150m from the water source. Not all wild asses were individually identified, but so far, we created 97 individual profiles (27♀ 70♂) based on photos, and recorded in which groups were they videotaped. Individuals were recognized with certainty up to 9 times, but 73 individuals were identified only once. Before reaching the water source, wild asses often aggregate in large groups and wait for the first few individuals to approach cautiously the water, and only then the rest of the individuals make a swift final approach. We did not consider these aggregations as social groups. We defined a group when individuals approached or left together the valley in which the water source is located. Female groups (including those with a male) were larger than male-only groups (9.8 and 5.1 individuals, range 2-49 and 1-34, respectively; P = 0.0191). Individuals appear on different days in groups of various sizes and compositions. The highest proportion of juveniles per female was seen in Nov. (0.74; P = 0.04) and this value is comparable to that found in the 1990’s study (0.75). Except for Sep., fewer adult females were observed compared to males (P = 0.028). Different daily activity patterns of the two sexes may explain this observation. The study of variation in social structure of wild Equids will enhance our understanding of the evolution of social systems in domestic horses and will improve the design of their boarding conditions (e.g., in better design of “Paddock Paradise”). Wild Asses that were reintroduced in the Negev Desert about 20 yrs ago show a social structure compatible with fission-fusion of groups. The ratio between juveniles and females did not change from an earlier study, soon after the release. Females were observed near the water source less frequently than males, possibly due to different activity patterns. The study of variation in social structure of wild equids will improve the design of boarding conditions for domestic horses.