Accumulation of humic-like and proteinaceous dissolved organic matter in zero-discharge aquaculture systems as revealed by fluorescence EEM spectroscopy
, 412 - 421. Publisher's VersionAbstract
Recirculating aquaculture systems (RAS), offering many economic and fish husbandry benefits, are characterized by an accumulation of dissolved organic matter (DOM) and, specifically, humic substances (HS). As reported in a number of studies, HS may affect biological activity in both invertebrates and vertebrates. Given the accumulation of HS in RAS, it is therefore of great interest to characterize DOM and, specifically, its HS fraction in the RAS. The present study was aimed at characterizing long-term changes in fluorescent DOM composition in the culture water of RAS systems, which were operated in a novel, zero water exchange mode. Two such zero-discharge recirculating systems (ZDS) were examined: a freshwater system, stocked with hybrid tilapia (Oreochromis aureus x Oreochromis niloticus) and a marine system, stocked with gilthead seabream (Sparus aurata). Excitation-emission matrices (EEMs) of fluorescence, coupled with parallel factor analysis (PARAFAC), were used to characterize and quantify the different DOM components in the ZDS. In the culture water, one tryptophan-like and four HS-like components were identified. The fluorescence intensities of three of the HS-like components as well as the tryptophan-like component increased at comparable rates during ZDS operation while a much slower accumulation of these compounds was observed in a parallel operated, flow-through, freshwater aquarium. The ZDS examined in this study comprised a sludge digestion stage where a considerable accumulation of all fluorescent components was detected. A HS-like components and a tryptophan-like component in blood of tilapia from the freshwater ZDS were similar to components found in the culture water. Blood levels of both components were higher in fish cultured in the DOM-rich ZDS than in fish raised in the control, flow-through freshwater aquarium. Fluorescence of the HS-like component found in the fish blood increased also with time of ZDS operation. The finding that fish blood contains a HS-like fluorescent component may have important implications for the understanding of the physiological effects of HS in fish and the possible benefits of these substances in aquaculture.
Combined adsorption and degradation of the off-flavor compound 2-methylisoborneol in sludge derived from a recirculating aquaculture system
, 69 - 77. Publisher's VersionAbstract
Off-flavor in fish poses a serious threat for the aquaculture industry. In the present study, removal of 2-methylisoborneol (MIB), an off-flavor causing compound, was found to be mediated by adsorption and bacterial degradation in sludge derived from an aquaculture system. A numerical model was developed which augmented Langmuir equations of kinetics of adsorption/desorption of MIB with first order degradation kinetics. When laboratory-scale reactors, containing sludge from the aquaculture system, were operated in a recirculating mode, MIB in solution was depleted to undetectable levels within 6 days in reactors with untreated sludge, while its depletion was incomplete in reactors with sterilized sludge. When operated in an open flow mode, removal of MIB was significantly faster in reactors with untreated sludge. Efficient MIB removal was evident under various conditions, including ambient MIB levels, flow velocities and sludge loads. When operated in an open flow mode, the model successfully predicted steady MIB removal rates with time. During steady state conditions, most of the MIB removal was found to be due to microbial degradation of the adsorbed MIB. Findings obtained in this study can be used in the design of reactors for removal of off-flavor compounds from recirculating aquaculture systems.
The protective effect of humic-rich substances from monogenean parasites infecting the guppy (Poecilia reticulata)
, 487 - 489. Publisher's VersionAbstract
The exposure of guppy fish (Poecilia reticulata), infected with the monogenea Gyrodactylus turnbulli and Dactylogyrus sp. to humic-rich culture water and feed, reduced both the infection prevalence (% of infected fish) and the infection intensity (parasites per fish) of the two parasites. Specifically, among fish exposed to: (a) humic-rich water and sludge from a recirculating system (RAS) and (b) synthetic humic acid (HA), infection prevalences of Gyrodactylus turnbulli were 17% and 25% respectively, as compared with an infection prevalence of 52% in the control group. The lower infection prevalence was accompanied by a significant reduction in the infection intensity: from 3.8 in the control group to 0.2 and 0.3 parasites per fish in the RAS and HA treated fish respectively. The infection prevalence and intensity of Dactylogyrus sp. were significantly lower (infection prevalence: 2.5%; infection intensity: 0.3 parasites/fish) in guppies exposed to RAS water and sludge than in the control group (infection prevalence: 50%; infection intensity: 0.8 parasites/fish).
The protective effect of humic-rich substances on atypical Aeromonas salmonicida subsp. salmonicida infection in common carp (Cyprinus carpio L.)
. Journal of Fish Diseases 2017
, 1783-1790. Publisher's VersionAbstract
Abstract When challenged with atypical Aeromonas salmonicida subsp. salmonicida, exposure of the common carp (Cyprinus carpio L.) to different humic-rich compounds resulted in a significant reduction in infection rates. Specifically, in fish exposed to (i) humic-rich water and sludge from a recirculating system, (ii) a synthetic humic acid, and (iii) a Leonardite-derived humic-rich extract, infection rates were reduced to 14.9%, 17.0% and 18.8%, respectively, as compared to a 46.8% infection rate in the control treatment. An additional set of experiments was performed to examine the effect of humic-rich components on the growth of the bacterial pathogen. Liquid culture medium supplemented with either humic-rich water from the recirculating system, the synthetic humic acid or the Leonardite humic-rich extract resulted in a growth reduction of 41.1%, 45.2% and 61.6%, respectively, as compared to the growth of the Aeromonas strain in medium devoid of humic substances. Finally, in a third set of experiments it was found that while the innate immune system of the carps was not affected by their exposure to humic-rich substances, their acquired immune system was affected. Fish, immunized against bovine serum albumin, displayed elevated antibody titres as compared to immunized carps which were not exposed to the various sources of humic substances.