Aquaculture fouling: Efficacy of potassium monopersulphonate triple salt based disinfectant (Virkon® Aquatic) against Ciona intestinalis

Toward integrated pest management in bivalve aquaculture

Pests of bivalve aquaculture are a challenging problem that can reduce productivity, profitability and sustainability. A range of pest management approaches have been developed for bivalve aquaculture, but a general absence of guiding frameworks has limited the scale and permanency of implementation. Applying principles of 'integrated pest management' (IPM) could change this paradigm to improve economic and environmental outcomes. We reviewed existing research and tools for pest management in bivalve aquaculture, with studies grouped under five pillars of IPM: pest ecology (25 studies), bioeconomic cost-benefits (4 studies), continual monitoring (17 studies), proactive prevention (32 studies) and reactive control (65 studies). This body of knowledge, along with insights from terrestrial agriculture, provide a strong foundation for developing and implementing IPM in bivalve aquaculture. For example, IPM principles have been applied by a regional collective of oyster farmers in the US Pacific Northwest to optimize pesticide application and search for other options to control problematic burrowing shrimps. However, IPM has not yet been broadly applied in aquaculture, and data gaps and barriers to implementation need to be addressed. Priorities include establishing meaningful pest-crop bioeconomic relationships for various bivalve farming systems and improving the efficacy and operational scale of treatment approaches. An IPM framework also could guide potential step-change improvements through directing selective breeding for resistance to pests, development of bespoke chemical control agents, applying emerging technologies for remote surveillance and farm management, and regional alignment of management interventions. © 2022 Society of Chemical Industry.

Degradation of sulfadiazine by UV/Oxone: roles of reactive oxidative species and the formation of disinfection byproducts

Sulfadiazine (SDZ) is a typical persistent sulfonamide antibiotic, which has been widely detected in natural drinking water sources. The degradation of SDZ by UV/Oxone (potassium monopersulfate compound) was explored in this study. The results showed that Cl^- can effectively activate PMS to promote rapid degradation of SDZ in the Oxone process by forming chlorine in the system. Radical quenching tests suggested that radical oxidation, including HO^•, SO₄^•-, and reactive chlorine species (RCS), played an important role by UV/Oxone. It further verified that concentration and distribution of HO^•, SO₄^•-, and RCS were pH-dependent; RCS act as a major contributor at pH 6.0 and pH 7.0 to degrade SDZ in this process. The SDZ degradation rate was firstly increased and then decreased by Cl^- and HCO₃^- (0-10 mM); HA (0-10 mg L^-1) exhibited insignificant influence on SDZ degradation. The degradation pathways of SDZ during UV/Oxone and formation pathways of five disinfection byproducts during subsequent chlorination were proposed. The possible DBP precursors formed by SO₂ extrusion, hydroxylation, and chlorination of SDZ during UV/Oxone pre-oxidation.

Experimental Evidence of Epizootic Epitheliotropic Disease Virus (Salmoid Herpesvirus-3, Alloherpesviridae) Transmission via Contaminated Fomites and Subsequent Prevention Using a Disinfectant

Epizootic epitheliotropic disease virus (EEDV) has caused considerable mortality in hatchery-reared lake trout Salvelinus namaycush in the Great Lakes Basin, and yet the routes of transmission and efficacious means of prevention remain poorly understood. To determine whether EEDV can be transmitted via contaminated fomites and clarify whether such transmission could be prevented via fomite disinfection, juvenile lake trout (n = 20 per treatment) were handled in nets previously soaked in an EEDV suspension (7.29 × 10⁴–2.25 × 10⁵ virus copies/mL of water) that were further immersed in either 1% Virkon^® Aquatic (“disinfected” treatment, in triplicate) or in sample diluent (“EEDV-contaminated” treatment). Negative control nets were soaked in sterile sample diluent only. Characteristic gross signs of EED developed in the “EEDV-contaminated” treatment group, which was followed by 80% mortality, whereas no gross signs of disease and 0–5% mortality occurred in the negative control and “disinfected” treatment groups, respectively. EEDV was detected via qPCR in 90% of the “EEDV-contaminated” treatment fish, however, it was not detected in any fish within the negative control or “disinfected” treatment groups. Study findings not only demonstrate that EEDV can be readily transmitted via contaminated fomites, but importantly suggest that Virkon^® Aquatic is an efficacious option for preventing EEDV contagion via the disinfection of hatchery tools, thereby highlighting a promising tool for improving lake trout hatchery biosecurity and minimizing EEDV-linked losses.

To treat or not to treat: a quantitative review of the effect of biofouling and control methods in shellfish aquaculture to evaluate the necessity of removal

The global growth of farmed shellfish production has resulted in considerable research investigating how biofouling compromises farm productivity. Shellfish fitness can be compared between fouled stock and stock which has undergone treatment. As treatment options are often harsh, they may deleteriously affect stock. The projected impact of biofouling may therefore be confounded by the impact of treatments. Given the substantial cost of fouling removal, some have questioned the necessity of biofouling mitigation strategies. Meta-analysis revealed that biofouling typically reduces shellfish fitness. However, the fitness of treated stock was often lower or equal to fouled control stock, indicating that many common antifouling (AF) strategies are ineffective at enhancing farm productivity. Overall, caution and diligence are required to successfully implement biofouling mitigation strategies. The need remains for increased passive prevention approaches and novel AF strategies suitable for shellfish culture, such as strategic siting of bivalve farms in areas of low biofouling larval supply.

Monitoring biofouling communities could reduce impacts to mussel aquaculture by allowing synchronisation of husbandry techniques with peaks in settlement

Fouling organisms in bivalve aquaculture cause significant economic losses for the industry. Managing biofouling is typically reactive, and involves time- and labour-intensive removal techniques. Mussel spat settlement and biofouling were documented over 20 months at three mussel farms within Port Phillip Bay (PPB), Australia to determine if knowledge of settlement patterns could assist farmers in avoiding biofouling. Mussel spat settlement was largely confined to a 2-month period at one farm. Of the problematic foulers, Ectopleura crocea settlement varied in space and time at all three farms, whilst Ciona intestinalis and Pomatoceros taeniata were present predominantly at one farm and exhibited more distinct settlement periods. Within PPB, complete avoidance of biofouling is impossible. However, diligent monitoring may help farmers avoid peaks in detrimental biofouling species and allow them to implement removal strategies such as manual cleaning, and postpone grading and re-socking practices, until after these peaks.

Tolerance of the invasive tunicate Styela clava to air exposure

Styela clava is a subtidal invasive marine species in Northern Europe, Atlantic Canada, Australia and New Zealand. It grows attached to solid substrata, including boat hulls, ropes, moorings, piers and aquaculture equipment, all of which can aid its spread to new locations. It interferes with feeding of mussels and oysters, and increases their harvesting costs. Being subtidal, it could be assumed that tunicates would rapidly die in air and thus exposure to air would be a practical method to prevent their spread on boats and equipment. This study tested their survival when exposed to air for up to (1) 120 h at a constant temperature of 10 °C, (2) shade ambient 15-27 °C, and (3) full sun ambient 15-29 °C. Humidity was consistently high (78-100%). The results indicated that survival was longer when the air temperature was cooler. Larger individuals of S. clava generally survived for longer out of seawater than smaller individuals. The results predict that two weeks of exposure to air for two weeks could be an effective management method to eradicate S. clava from marine equipment when the air temperature is 10 °C. However, drying time would be less under conditions of low humidity and under direct sunlight.

Biofouling leads to reduced shell growth and flesh weight in the cultured mussel Mytilus galloprovincialis

Competitive interactions between cultured mussels and fouling organisms may result in growth and weight reductions in mussels, and compromised aquaculture productivity. Mussel ropes were inoculated with Ciona intestinalis, Ectopleura crocea or Styela clava, and growth parameters of fouled and unfouled Mytilus galloprovincialis were compared after two months. Small mussels (≈ 50 mm) fouled by C. intestinalis and E. crocea were 4.0 and 3.2% shorter in shell length and had 21 and 13% reduced flesh weight, respectively, compared to the controls. Large mussels (≈ 68 mm) fouled by S. clava, C. intestinalis and E. crocea were 4.4, 3.9 and 2.1% shorter than control mussels, respectively, but flesh weights were not significantly reduced. A series of competitive feeding experiments indicated that S. clava and C. intestinalis did not reduce mussels' food consumption, but that E. crocea, through interference competition, did. Fouling by these species at the densities used here reduced mussel growth and flesh weight, likely resulting in economic losses for the industry, and requires consideration when developing biofouling mitigation strategies.

Preventing ascidian fouling in aquaculture: screening selected allelochemicals for anti-metamorphic properties in ascidian larvae

Fouling by ascidians causes major stock losses and disrupts production in marine aquaculture, especially bivalve aquaculture. Currently, no cost effective solution exists despite the testing of many prospective control techniques. This study examined a range of allelochemicals suspected to inhibit metamorphosis in marine larvae. Five allelochemicals were screened in a larval metamorphosis bioassay using Ciona savignyi Herdman to determine their potential as a remedy for ascidian fouling in bivalve aquaculture. Three of the compounds tested inhibited ascidian larval metamorphosis and increased mortality at low concentrations. These were radicicol (99% inhibition of metamorphosis [IC₉₉], 0.8 μg ml⁻¹; 99% lethal concentration [LC₉₉], 2.5 μg ml⁻¹; 99% lethal time [LT₉₉], 7.0 days), polygodial (IC₉₉, 0.003 μg ml⁻¹; LC₉₉, 0.9 μg ml⁻¹; LT₉₉, 6.4 days), and ubiquinone-10 (IC₉₉, 3.2 μg cm⁻²; LC₉₉, 14.5 μg cm⁻²; LT₉₉, 5.6 days; expressed as μg cm⁻² due to insolubility in water and ethanol). While spermidine significantly affected metamorphosis and mortality of C. savignyi, the effect was insufficient to achieve inhibition in 99% of larvae over the 7-day timeframe of the assay. Muscimol did not affect metamorphosis or mortality at the concentrations tested. The present study demonstrates that radicicol, polygodial and ubiquinone-10 have potential for future development in antifoulant formulations targeted towards the inhibition of metamorphosis in ascidian larvae, while spermidine and muscimol appear unsuitable.