Open-water Aquaculture Research Articles

A Control Architecture for Developing Reactive Hybrid Remotely Operated Underwater Vehicles

This article introduces a control architecture designed for the development of Hybrid Remotely Operated Underwater Vehicles. The term ”Hybrid” characterizes Remotely Operated systems capable of autonomously executing specific operations. The presented architecture maintains teleoperation capabilities while enabling two fully autonomous applications. The approach emphasizes the implementation of reactive navigation by exclusively utilizing data from a Mechanical Scanned Imaging Sonar for control decisions. This mandates the control system to solely react to data derived from the vehicle’s environment, without considering other positioning information or state estimation. The study involves transforming a small-scale commercial Remotely Operated Underwater Vehicle into a hybrid system without structural modifications, and details the development of an intermediate Operational Control Layer responsible for sensor data processing and task execution control. Two practical applications, inspired by tasks common in natural or open-water aquaculture farms, are explored: one for conducting transects, facilitating monitoring and maintenance operations, and another for navigating toward an object for inspection purposes. Experimental results validate the feasibility and effectiveness of the authors’ hypotheses. This approach expands the potential applications of underwater vehicles and facilitates the development of Hybrid Remotely Operated Underwater Vehicles, enabling the execution of autonomous reactive tasks.

Persistent Dysbiosis, Parasite Rise and Growth Impairment in Aquacultured European Seabass after Oxytetracycline Treatment.

The use of antibiotics in open-water aquaculture is often unavoidable when faced with pathogens with high mortality rates. In addition, seasonal pathogen surges have become more common and more intense over the years. Apart from the apparent cost of antibiotic treatment, it has been observed that, in aquaculture practice, the surviving fish often display measurable growth impairment. To understand the role of gut microbiota on the observed growth impairment, in this study, we follow the incidence of Photobacterium damselae subsp. piscicida in a seabass commercial open-water aquaculture setting in Galaxidi (Greece). Fish around 10 months of age were fed with feed containing oxytetracycline (120 mg/kg/day) for twelve days, followed by a twelve-day withdrawal period, and another eighteen days of treatment. The fish were sampled 19 days before the start of the first treatment and one month after the end of the second treatment cycle. Sequencing of the 16S rRNA gene was used to measure changes in the gut microbiome. Overall, the gut microbiota community, even a month after treatment, was highly dysbiotic and characterized by very low alpha diversity. High abundances of alkalophilic bacteria in the post-antibiotic-treated fish indicated a rise in pH that was coupled with a significant increase in gut parasites. This study's results indicate that oxytetracycline (OTC) treatment causes persistent dysbiosis even one month after withdrawal and provides a more suitable environment for an increase in parasites. These findings highlight the need for interventions to restore a healthy and protective gut microbiome.

Numerical simulation of the environmental impacts of open water aquaculture

Numerical simulation of the environmental impacts of open water aquaculture

Does aquaculture aggravate exotic fish invasions in the rivers of southern China?

Human-induced fish introduction in aquaculture always be considered the most important driver of biological invasions in freshwater ecosystems, yet most introduced species fail to establish though having great economic benefits. Explaining the varying success of introduced fish species is a central question both in invasion biology and aquaculture management. Southern China is a good region to test the invasion hypotheses where lots of non-native fish species were cultured and invaded. In this study, we used four human activities related to aquaculture to test their effects on the establishment of non-native fish species in the rivers of southern China. Our results showed that: open-water aquaculture significantly increased the establishment probabilities of non-native species relative to standardised aquaculture in ponds; the establishment and spread of non-native fish species in rivers had no significant correlation to their production and distribution in standardised aquaculture; non-native fish species with low economic value were more prone to escape and establishment in natural rivers, and had higher establishment probabilities in rivers due to the lower fishing pressure. These results indicate that standardised aquaculture and cultivated species with high economic value do not always result in biological invasions. To mitigate the invasion of exotic species caused by aquaculture, stricter management practices and more optimized economic assessments should be implemented for the introduction and cultivation of non-native fish species.

Wild fish of aquaculture importance, as new host for isopod Tachaea spongillicola Stebbing, 1907 infestation with emphasis on prevalence and histopathology: A case report

The study reported an ectoparasitic isopod, Tachaea spongillicola infestation in fish as new host, in wild caught species of Labeo rohita and Cirrhinus mrigala of family Cyprinidae and Notopterus notopterus of family Notopteridae from reservoir ecosystem. The prevalence of infestation was 100% in all the three fish species with mean intensity 29% for C. mrigala followed by 25% in L. rohita and 11% in N. notopterus. The Mann-Whitney U test analysis showed a significant (p < 0.01) difference between C. mrigala and N. notopterus, and L. rohita and N. notopterus, while no significant (p = 0.15) difference was observed between C. mrigala and L. rohita, underlining the preference of parasitic infestation towards carps species, that contributes a major share to the world's fish production. T. spongillicola infestation resulted in interesting pathology of conspicuous gill lamellae necrosis, like chondroptosis, and thinning of cartilaginous matrix resulting in curvature of primary gill lamella were recorded. In addition, rupture of pillar cells, erythrocytes migration through epithelial rupture, hypertrophied erythrocytes, extensive proliferation and hypertrophy goblet cells were observed in gills. Till date, Tachaea spp. is being reported as ectoparasites in shrimps and with few cases in sponges. This is the first report of Tachaea sp. viz. Tachaea spongillicola as ectoparasite, recorded in fish species, since after 114 years of its first record in freshwater sponge. As these fish species particularly of Indian major carps, are widely cultured in South Asian and Southeast Asian countries, knowledge on T. spongillicola infestation in fish would add on parasitic diseases list for better preparedness in open water aquaculture system.

Discrete water quality sampling at open-water aquaculture sites: limitations and strategies

While environmental performance of cage-based aquaculture is most often monitored through benthic conditions, there may also be requirements that necessitate discrete, pelagic sampling. In the pelagic realm, adequately capturing the spatial and temporal dynamics of interest and attributing causality to aquaculture processes can be extremely challenging. Conditions are seldom ideal, and data adequacy concerns of discrete samples collected at open-water aquaculture sites are not uncommon. Further exploration of these challenges is needed. Herein, we aim to explore considerations for study design, analysis, and data interpretation of discrete pelagic sampling. As examples, we present 2 case studies where limited sampling occurred under conditions of complex pelagic dynamics. A Norwegian case study quantified particle abundance around salmon farms, and aimed to highlight the effects of spatial−temporal variation on sampling design, the need for inclusion of companion parameters, and the benefits of a priori and a posteriori data interpretation strategies. A Canadian case study collected discrete samples to measure ammonium concentrations with continuous current measurements at an Integrated Multi-Trophic Aquaculture (IMTA) farm, to explore issues of complex hydrodynamics, reference site suitability, sampling resolution, data pooling, and post hoc power tests. We further discuss lessons learned and the implications of study design, ambient conditions, physical processes, farm management, statistical analysis, companion parameters, and the potential for confounding effects. Pragmatic consideration of these aspects will ultimately serve to better frame the costs and benefits of discrete pelagic sampling at open-water aquaculture sites.

A Sustainability Index of potential co-location of offshore wind farms and open water aquaculture

This paper presents the definition of a Sustainability Index for the co-location in marine areas of offshore wind farms and aquaculture plans. The development of the index is focused on the application of MCE technique based on physical constraints and biological parameters that are directly linked to the primary production. The relevant physical factors considered are wind velocity and depth range (which directly governs the choice of the site for energy production and for offshore technology), the relevant biological parameters are SST, SST anomaly and CHL-a concentration (as a measurement of the productivity). The further development of the technique, already used in open water aquaculture localization, consists in converting raw data into sustainability scores, which have been combined using additive models, in order to define the overall sustainability. The study area used to implement the computation of the Sustainability Index (SI) was identified in the Danish portion of the Baltic Sea and in the western part of the Danish North Sea. Results on the spatial distribution of the SI underline different responses as a function of the physical and biological main influencing parameters.

Dietary Proportion of Fish Culture Solids Required by Shellfish to Reduce the Net Organic Load in Open-Water Integrated Multi-Trophic Aquaculture: A Scoping Exercise with Cocultured Atlantic Salmon (Salmo salar) and Blue Mussel (Mytilus edulis)

ABSTRACT Integrated multi-trophic aquaculture (IMTA) aims to recapture portions of nutrient waste lost from 1 species as nutritional inputs for another. This process has the potential to augment growth of cocultured species while reducing the nutrient load from an aquaculture site. In several jurisdictions, open-water aquaculture is regulated through measures of benthic hydrogen sulfide concentrations, which is proportional to excess deposition of organic material such as feces and uneaten food. Interception, consumption, and digestion of organic portions from the fed trophic level (e.g., fish) by organic extractive species (e.g., shellfish, deposit feeders) results in “organic stripping,” with less organic material in resulting feces, thereby reducing the net organic load and benthic deposition potential. Shellfish are deployed beside fish cages in some openwater IMTA systems. In addition to the potential consumption of fish culture solids (i.e., feces, feed “fines”), natural particles (i.e., seston) wil...

Manipulation of environmental variables and the effect on the growth of Haliclona sp.: Implications for open-water aquaculture

We examined how the physical environment influences the growth and survival of an undescribed Haliclona species. To determine the influence that water movement, light and sediment had on the sponge, explants of Haliclona sp. (approximately 8 cm3 in size) were transplanted into manipulated microenvironments at Hamelin Bay on the west coast of Western Australia near Perth. The sponge is typically found under limestone ledges and appears to have distinct limits on the microenvironment in which it is found. A three-factor orthogonal design was used to manipulate levels of light, water flow and sedimentation. Each factor had two experimental levels, creating environments with high and low water movement, high and low light, and upward and downward orientations to control sediment levels. The survival of explants was high (100%). However, all explants showed a regression in weight. Explants transplanted on to the underside of horizontal surfaces (downward orientations) demonstrated significantly less weight loss (P = 0.023), which was attributed to lower sediment exposure. Light and water movement did not significantly influence the sponge's growth.

Effects of intensive seaweed farming on the meiobenthos in a tropical lagoon

Open water aquaculture of the seaweed Eucheuma spinosum, imported to Zanzibar from the Philippines in 1989, is presently a large scale operation on the island, with algal farms covering around a 1000 ha of the intertidal area. To assess the effects of the farming on benthic communities both field and laboratory studies were conducted. Two field studies conducted at different times showed that all major meiofaunal taxa were found in significantly lower numbers within the farm area compared with control areas. Multidimensional scaling ordination of nematode species, genera and family abundance data separated samples from farmed and control areas. There was a significant difference in the nematode assemblage structure among areas in pairwise comparisons using ANOSIM. The trophic structure of the nematode assemblage was characterised by a high number of epistrate feeders in all areas ranging from 73 to 96% of total numbers in the samples. To test the hypothesis that toxic substances excreted by the seaweed were responsible for lower abundance inside the farm area, a laboratory experiment was conducted. Eucheuma plants were added to several microcosms and allowed to grow there for 40 days. The results indicated no effects of the seaweed on the density of the major infauna taxa as no significant difference was found among the treatments. It is concluded that other factors such as increased predation by benthic feeding fish and the mechanical disturbance of the sediments may better explain the observed differences in infauna abundance inside and outside the algal culture farms.