Runoff of foliar-applied natural fungicides in aquaponics: Implications for fish and nitrification.

Aquaponics is a method of producing food in a sustainable manner through the integration of aquaculture and hydroponics, which allows simultaneous cultivation of fish and economic crops. The use of natural fungicides are crucial to the sustainable control of diseases in aquaponics. We assessed the potential impacts of natural fungicides, such as clove oil and lecithin, as well as a synthetic fungicide, tebuconazole, following foliar application in aquaponics. This study examined the runoff rates of the fungicides in decoupled aquaponics, and the subsequent effects of the runoffs on nitrification processes and Nile tilapia (Oreochromis niloticus). The runoffs of the foliar-applied fungicides, clove oil, lecithin, and tebuconazole, were detected in aquaponics water at a percentage runoff rate of 0.3 %, 2.3 %, and 0.3-0.8 % respectively. In the biofilter, lecithin altered the ammonium levels by increasing ammonium-nitrogen levels by 7 mg L-1, 6 h post application. Clove oil, on the other hand, showed no significant effect on ammonium, nitrite, and nitrate-nitrogen. Similarly, the toxicity test showed that eugenol had no significant effects on the hematological, biochemical and antioxidative activities of O. niloticus. Conversely, tebuconazole exhibited significant and persistent effects on various biochemical parameters, including lactate, albumin, and total protein, as well as hematological parameters like hemoglobin and MCH. The use of lecithin and tebuconazole should only be limited to decoupled aquaponics.

Diversity and distribution of Aphanomyces astaci in a European hotspot of ornamental crayfish introductions.

Ornamental trade has become an important introduction pathway of non-native aquatic species worldwide. Correspondingly, there has been an alarming increase in the number of established crayfish of aquarium origin in Europe over the previous decade. The oomycete Aphanomyces astaci, the pathogen causing crayfish plague responsible for serious declines of European crayfish populations, is dispersed with introduced North American crayfish. The role of ornamental taxa in introducing and spreading different genotypes of this pathogen in open waters remains unclear. We investigated the distribution, prevalence, and diversity of A. astaci in Budapest, Hungary, which became a hotspot of aquarium crayfish introductions. Their establishment in this area was facilitated by locally abundant thermal waters. We screened for A. astaci in six host taxa from 18 sites sampled between 2018 and 2021: five cambarids (Cambarellus patzcuarensis, Faxonius limosus, Procambarus alleni, P. clarkii, P. virginalis) and one native astacid (Pontastacus leptodactylus). The pathogen was confirmed at five sampled sites in four host taxa: P. virginalis, P. clarkii, F. limosus, and for the first time in European open waters also in P. alleni. Genotyping was successful only in individuals from two different brooks where multiple host species coexisted but revealed unexpected patterns. Mitochondrial B-haplogroup of A. astaci, previously usually reported from Pacifastacus leniusculus or infected European species, was detected in P. virginalis at both sites, and in both F. limosus and P. virginalis sampled from a thermally stable tributary of Barát brook in 2018. In contrast, A-haplogroup of A. astaci was detected in coexisting F. limosus, P. virginalis and P. clarkii sampled in the same watercourse just a few hundred meters downstream in 2020. Additional genotyping methods indicated that a previously unknown A. astaci strain was associated with the latter haplogroup. One P. virginalis individual from 2020 was apparently co-infected by strains representing both mitochondrial haplogroups. The results indicated multiple sources of A. astaci in Budapest, likely directly associated with the introduction of ornamental species, interspecific transmission of this pathogen among ornamental hosts, and potential for a quick spatial or temporal turnover of dominant A. astaci strains at a certain locality. This highlights that in regions with high richness of potential A. astaci hosts, host taxon/pathogen genotype combinations become unpredictable, which might prevent reliable genotyping of pathogen sources in local crayfish mass mortalities.

Are bold-shy personalities of European perch (Perca fluviatilis) linked to stress tolerance and immunity? A scope of harnessing fish behavior in aquaculture.

The sensitivity to stress and its impact on immunity are supposedly related to a fish's personality. In the present study, European perch (Perca fluviatilis) were exposed to an open-field and a novel-object test to identify distinctive shy and bold individuals. This series of cognitive tests revealed clear differences between proactive individuals with pronounced exploration behavior (bold personality) and reactive individuals that took a freeze-hide position (shy personality). A cohort of shy and bold perch was then exposed to elevated stocking density. Frozen activity and lower explorative behavior were related to higher basal and stocking-induced cortisol levels compared to proactive individuals. Since cortisol is a well-known modulator of immune-gene expression, we used multiplex real-time PCR to profile the differential immune responses to the intraperitoneal injection of Aeromonas hydrophila in the head kidney and peritoneal cells of bold and shy perch individuals. These expression differences between stimulated bold and shy perch were generally modest, except for the genes encoding the complement component c3 and the matrix metallopeptidase mmp9. The strong differential expression of these two bactericidal and inflammatory genes in the context of the modestly regulated features suggests that a fish's personality is linked to a particular immune-defense strategy. In conclusion, our approach, based on behavioral video observations, phagocytosis and enzyme assays, immunogene-expression profiling, and quantification of stress-relevant metabolites, revealed indications for divergent coping styles in cohorts of bold or shy European perch. This divergence could be exploited in future selective breeding programs.

The economic viability of commercial-scale hydroponics: Nigeria as a case study.

The use of hydroponics to cultivate economic crops is an emerging agricultural practice in Nigeria. There is, however, a paucity of information on the economic viability and valuation of the production systems. This study investigated hydroponics' profitability and economic viability under small- and medium-scale production systems. The economic viability of ten hydroponic farms were evaluated using the financial metrics: net present value (NPV), internal rate of return (IRR), benefit-cost ratio (BCR), and sensitivity analysis. Sensitivity analysis based on positive and negative changes in the running cost and gross annual revenue was adopted to measure the robustness of the production method. The positive NPVs of the small-scale farmer (€42,895) and medium-scale farmer (€331,465) at a 15% discount rate show that both production scales are economically viable. The ten-year IRR of both production scales was about 83%. Similarly, the BCR showed that both the small-scale farmers (5.07) and the medium-scale farmers (4.91) are significantly profitable. In the sensitivity analysis, the small-scale farmers were more sensitive to recurrent 5% changes in the running cost at the 13% threshold. On the other hand, medium-scale farmers were less sensitive with a threshold value of 58.4%. Similarly, small-scale farmers are more sensitive to a 15% reduction in the gross annual revenue, with a negative net return of -€956. It is imperative to state that, though starting an investment in hydroponics requires a high initial investment, medium-scale farmers would be less sensitive to changes in the running cost of production in the face of uncertainties.

The Effect of Different Feeding Applications on the Swimming Behaviour of Siberian Sturgeon: A Method for Improving Restocking Programmes.

Restocking programmes of different fish species have been implemented worldwide. However, the survival of hatchery-reared fish after release to riverine ecosystems is at a very low level. One of the reasons for the high mortality rate of post-released fish is their modified swimming behaviour due to the hatchery rearing practice. To investigate one of the possible causes for modified swimming behaviour, Acipenser baerii larvae were exposed to surface- and bottom-feeding applications with day and night light regimes in a factorial design. We also analysed the effect of 5 and 10 days of starvation after different feeding applications on sturgeon swimming behaviour. The surface-feeding application was previously expected to promote the frequent Siberian sturgeon swim up to the mid- and top-water layers in our rearing facilities. However, our results indicated that the modified behaviour of the Siberian sturgeon in our study was caused by fish starvation and a possible predator-free environment rather than by the method of feed application or the day/night light regimes. These results may be used to improve the implementation of restocking programmes either through modified hatchery rearing practice or the training of foraging skills with predator stimuli.

The Invasive Round Goby Neogobius melanostomus as a Potential Threat to Native Crayfish Populations.

Despite the spread of round goby Neogobius melanostomus into freshwater streams, there is a lack of information with respect to its effect on macroinvertebrate communities, especially crustaceans. We studied foraging efficiency of N. melanostomus on Procambarus virginalis and Asellus aquaticus, using a functional response (FR) approach. Stocking density of the prey species was manipulated to determine its effect on consumer utilization, with prey offered separately or combined at 1:1, 3:1, and 1:3 at each tested density. For both prey species, N. melanostomus exhibited type II FR, occasionally with a high proportion of non-consumptive mortality. Procambarus virginalis suffered a significantly higher attack rate compared to A. aquaticus. Neogobius melanostomus killed significantly more of the most prevalent prey, regardless of species. In trials with prey species of equal proportions, a difference in the number of each species killed was observed only at the highest density, at which P. virginalis was preferred. Neogobius melanostomus may be an important driver of population dynamics of prey species in the wild. The non-selective prey consumption makes N. melanostomus a potential threat to macrozoobenthic communities of river tributaries.

Distribution of alien animal species richness in the Czech Republic.

Biogeographical barriers formed by natural forces over billions of years have been substantially disrupted by human activity, particularly in recent centuries. In response to these anthropogenic changes, global homogenization of biota is observed at an ever-increasing rate, causing environmental and economic losses as well as emerging health risks. Identifying factors underlying alien species richness is essential for prevention of future introductions and subsequent spread. In this study, we examined the effects of environmental and human-related factors on distribution of alien animal species richness in the Czech Republic (Central Europe). We compiled a set of maps showing the level of invasion of six categories of alien animal species in each of 628 grid cells (ca. 12.0 × 11.1 km) covering the Czech Republic. Relationships between alien species richness and 12 variables characterizing climatic conditions, topography, land cover, and human population size were calculated using the generalized least squares method. Species richness of all alien species, of invertebrates, and of terrestrial species showed the strongest positive relationship with mean annual temperature, while the number of black and grey (proposed prominent invaders) and aquatic species was most closely related to the presence of large rivers. Alien vertebrates showed a strong negative relationship with annual precipitation. The highest alien animal species richness was found in and near large population centers and in agricultural landscapes in warm and dry lowlands. The gateways for alien aquatic species are rather large rivers over sport fishing and aquaculture import. Compiled maps create a powerful visual communication tool, useful in development of programs to prevent future introductions.