5. Sustainability in Marine and Coastal Fish Farming

To increase the production of aquatic organisms, it is necessary to raise the stocking density in the cultivation facilities. Cultivation at high densities can cause negative environmental repercussions like as chemical and biological pollution, disease outbreaks, unsustainable feeding, and competition for coastal area and may also compromise, to a certain extent, the environment ^[33].

Jiang et al. ^[34] developed a food-energy-water-carbon (FEWC) sustainability index, from 0 to 100, to assess the global sustainability of aquaculture among countries. Results indicate that the overall sustainability of global aquaculture is low (average score = 26) with none achieving a high sustainability score (75–100) and almost all practicing aquaculture in a relatively low sustainable way (0–50). Considering the sub-sustainability at a sector level, 80% of countries had at least two sectors among FEWC falling into the low sustainable zone (score less than 25). China led all countries by contributing to more than half of global aquaculture water consumption and greenhouse gas emissions, followed by India and Indonesia.

5.1. Classical Methods to have Fish Farming More Sustainable

Among the most sustainable practices in fish farming, researchers can highlight the use of moderate densities, feeding strategy and location, verified through the level of cortisol in fish, an indicative factor of stress in farmed animals, observed, for example, by Hanke et al. ^[35].

Kumaran et al. ^[36] observed favorable technical indicators (fish survival, feed conversion, growth rate and productivity), economic parameters (cost-benefit ratio, payback period and internal rate of return) and indicators of livelihood security in the cultivation of barramudi L. calcarifer when cultivated in the three-phase system in India, comprising larviculture, pre-growing and final grow-out in cages, and thus showed that this system is technically and economically viable, socially acceptable and, therefore, sustainable.

Calleja et al. ^[37] found a high potential for marine aquaculture, specifically for large and medium-sized enterprises. Three out of each five species studied show high suitability in most study sites (Central and Northern Pacific coast of Costa Rica) and the other two species show promising results in the Gulf of Nicoya. At a regional scale, the Pacific coast of Costa Rica presents high potential for fish aquaculture, being a promising development medium for coastal communities as long as it is environmentally sustainable and compatible with other coastal activities such as tourism.

5.1.2 IMTA

Another point to comment is the discharge of effluents from aquaculture, mostly obtained through the foods used in cultivations, which can greatly affect the environment if not treated correctly. Based on this notion, the IMTA (Integrated Multi-Trophic Aquaculture) concept was developed, which applies a simplified food web structure to a farming system of fed-species, such as fish and shrimp, in conjunction with extractive organisms, such as mollusks and seaweed, which suck up particles and nutrients from the environment ^[38]. On this point, when designing an effluent treatment unit, such as a recirculation system (RAS), use of macrophytes or adsorbents, fish farmers must consider a variety of factors. Through appropriate treatment methods, the objective is to reduce environmental pollution ^[39]. A greater input, mainly, of nitrogen and phosphorus in aquatic ecosystems will be evidenced in eutrophic environments, which means an increase in primary production in water bodies ^[39].

Current RAS knowledge and technology make these systems viable and economical only for the production of high-value species at the moment, but other aquatic species may become sustainable with alternative choices like as aquaponics. Many present and future advancements in renewable energy production will lower RAS operating costs. To lower RAS costs, aquaculture producers, scientists, and engineers must collaborate to properly design and constantly improve every component of RAS. Through research and field tests, greater information about RAS technology is gathered, as also a better understanding of the interplay between its numerous components. RAS technology will continue to alter and modernize the aquaculture sector, including local production in or near metropolitan areas, as well as in locations and nations with limited water resources, where more traditional aquaculture systems will be implemented ^[40].

5.2. Technological Evolution in Fish Farming

Industry 4.0 is associated with engineering and computer science knowledge coupled with multisensory schemes for aquaculture systems associated with online servers and/or workstations with the most appropriate software to manage and control the system, thereby contributing to improved aquaculture productivity and efficiency while lowering overall costs ^[41]. Aquaculture 4.0 technologies are a long-term solution for increasing production (quantity and quality) while decreasing expenses and pollution in aquaculture ^[42]. Because aquaculture can be offshore or onshore, abiotic and biotic factors influence the aquaculture system, which has a high influence on aquaculture productivity. The 4.0 technologies and methods must be developed to deal with the environmental demand from the aquaculture location and species cultivated ^[43].

Numerous technologies are now being used in different domains that can be included in Aquaculture 4.0: Recirculation Aquaculture Systems (RAS), smart aquacultures (offshore and onshore), and real-time water quality ^[41].

Aquaculture 4.0 programmes provide farmers with real-time monitoring of water quality and aquaculture conditions. These systems can provide a large amount of information at intervals of seconds or minutes, allowing for more accurate planning of aquaculture activities and the possibility of prompting alarms in case of unsafe water conditions/quality or weather alerts (e.g., allowing the offshore systems to descend the fish cages to deep sea weight, reducing the negative effects of sea waves and bad weather in the aquaculture system). Also, the creation of a comprehensive database that will aid in precise and specialised research to improve the efficiency of aquaculture over the medium and long term, minimising risks and elevating fish farming productivity.

One of the key benefits of aquaculture 4.0 is the remote control and viewing of the RTD on a cloud-based platform, particularly in marine farms where cages cannot always be entered quickly and at the desired moment. Onshore fish farmers applaud the cloud-based system of onshore aquaculture characteristics, which can be accessible from anywhere ^[41]. Thus, the evolution of the fish farm pass for an adaptation to IMTA protocol to reduce wastes in the aquatic systems.

Offshore aquaculture is still a new business that needs to include additional technology, such as artificial intelligence and augmented reality, that can improve and automate numerous activities remotely, such as feeding, sampling, monitoring, and surveillance. More study on the implications and repercussions of offshore aquaculture on seafood security and marine habitats, as well as the social dimensions and effects of offshore aquaculture, is required.

5.3. Feed and Nutrition in Fish Farming

Rising fish feed prices, as well as the environmental consequences of over-harvesting forage fish for feed and fish oil, have led to a rise in the rearing of herbivorous fish (carp and tilapia) and omnivorous fish (barramundi), which use significantly less fishmeal to generate protein. Furthermore, antibiotics or pesticides used on farmed fish can have an impact on other marine species or human health. These nutrients and pollutants fall to the ocean floor, where they may have an influence on the biodiversity. Meanwhile, research to discover alternatives to fishmeal feed or methods to make it more sustainable is continuing. Thus, finding the finest fish feed formulae also include attempting to attain the lowest feed conversion ratio—the amount of feed supplied in relation to the weight acquired by the fish ^[44].

The production of feed based on new ingredients is important due to raw materials for feed increase price and sustainability, therefore, there is an increase to exploit more sustainable and economic raw source for feeds. At this moment, vegetables (non-competing vegetables for animal feed or human food) and insects based feeds can be an economic and efficient alternative to the traditional feeds ^[45]. Thus, the exploitation of microalgae, macroalgae, bacteria, yeast, and insects can substitute the actual forage fish, particularly in high-value species such as salmonids, will be critical for fed aquaculture sustainability ^[45]. Furthermore, nutrition is vital player in fish farming economy, since feed accounts for almost half of the variable production cost. In recent years, fish nutrition has evolved substantially with the development of new, balanced commercial diets that support optimal fish growth and health. The creation of novel species-specific diet formulas helps the aquaculture sector expand to meet rising demand for economical, safe, high-quality fish and seafood ^[46].

Other of the aquaculture problem is overfeeding, which wastes valuable feed. Water contamination, low dissolved oxygen levels, higher biological oxygen demand, and increased bacterial loads are other consequences. Fish should typically be fed simply the quantity of feed that they can ingest fast (in less than five to 10 minutes). A decent general rule of thumb is to give the fish around 80% of what they want to consume (satiation). In this method, you feed for one day as much as the fish will ingest on a regular basis, possibly twice a month ^[46]. Thus, the new feed need to have higher nutritional values.

Due to the antibiotics and pharmaceuticals restriction used in the fish cultivation. The industry's future development is heavily reliant on the sustainable use of natural resources. Nutraceuticals are being used in aquaculture to improve disease resistance, growth performance, food conversion, and product safety for human consumption. Probiotics boost growth and feed conversion, enhance health, promote disease resistance, reduce stress sensitivity, and boost overall vigor. Currently, the majority of nutraceuticals come from terrestrial sources rather than fish. Host-associated (autochthonous) nutraceuticals, on the other hand, are expected to be more durable in the gastrointestinal system of fish and, as a result, may have longer-lasting benefits on the host. Nutraceuticals candidates are often evaluated in vitro, however the transition to in vivo testing is frequently difficult ^[47]

Although, the administration of adequate doses of immunostimulants or immunomodulatory agents promotes an increase in resistance to different diseases and improves the animals' health status. Some studies demonstrate that the administration of an optimal dose of an immunostimulant is extremely important to obtain an effective response. These effects were proven in the cultivation of Asia seabass (Lates calcarifer), and the Kappaphycus alvarezii (Rhodophyta) addition showed an excellent immunostimulatory activity, constituting a good immunostimulant/immunomodulating agent in the fish aquaculture field, although more trials are needed ^[48].

The use of natural substances capable of immunomodulating the fish reaction to stress factors, combined with good management of cultivation, emerges as a promising tool for aquaculture, as it promotes action against the negative effects, reducing mortality during the production process of these organisms.

5.4. Biosecurity in Fish Farming

According to FAO, biosecurity is a comprehensive and integrated strategy that encompasses both policy and regulatory frameworks aimed at analysing and managing relevant hazards to human, animal, and plant life and health, as well as associated environmental problems. It is a comprehensive concept that addresses food safety, zoonoses, the introduction and management of animal and plant illnesses, as well as invasive alien species. It also addresses the introduction and dissemination of live modified organisms and their by-products ^[49]. Failure to apply biosecurity can result in disease outbreaks, which, as previously said, can reduce farm output, pose hazards to human health, give fish a terrible flavour and look, and obstruct farm access to markets. All of this, of course, reduces a farmer's cash return. Globalization, for example, has increased the risk of disease spread due to the increased volume, diversity, and social-economical relevance of aquatic animal trafficking. Several stages must be performed in order to build a successful biosecurity plan. These processes are as follows: hazard identification and prioritisation; risk-impact assessment; identification, mitigation, management, and remediation of critical control points through which diseases may enter or leave the epidemiological unit; development of a contingency plan if a disease is discovered in the unit through disease surveillance, monitoring, and determination of disease status or freedom in the epidemiological unit; and periodic audition of procedures. Veterinarians test these procedures, and government veterinary authorities should evaluate and approve them ^[50].

Aquaculture has been demonstrated to have the potential to contribute to socially beneficial global food production. However, in order to address the expanding global food security issues, the aquaculture blue revolution must be accelerated, but corrective techniques to mitigate its negative repercussions must also be developed. While contributing to global food production and boosting per capita animal protein intake, aquaculture has depleted resources that sustain regional and global food security in some circumstances. Indeed, certain aquaculture methods are viewed as a danger to food security ^[51].

Most aquaculture laws and certification programmes are geared toward individual farms. Even if everyone follows the rules, having a large number of producers in the same location might have a cumulative environmental impact, such as water pollution or fish infections. Spatial planning and zoning can help to guarantee that aquaculture activities stay within the carrying capacity of the surrounding environment while also reducing disputes over resource usage. For example, Norway's zoning restrictions guarantee that salmon farmers are not unduly concentrated in one location, decreasing disease risk and helping to manage environmental repercussions.

Many fishponds in China, Thailand, and Vietnam have been converted from rice fields, a practise that China has since prohibited owing to national food security concerns. More crucially, it represents a change from producing a main food crop for local populations to producing a commodity for the export market, and so food security is a major concern for some small farmers who have converted good rice fields into fish farms ^[52].

According to Beveridge et al. ^[53], the contribution of aquaculture to food security is dependent not only on where it happens, but also on culture species, product price, and fish size - all of which impact availability and usage by poor customers. Farmers can be incentivized to conduct more sustainable aquaculture through a range of governmental and commercial programmes. Thailand's government, for example, has offered free training, water supply, and wastewater treatment to shrimp farmers working lawfully in aquaculture zones. The government has also offered low-interest loans and tax breaks to small-scale farmers, assisting them in adopting superior technology that has enhanced production and decreased the need to clear additional land ^[54]. Thus, to inspire farm workers to execute biosecurity measures, they should be instructed on biosecurity by reputable and credible sources, such as veterinarians, so that they understand the benefits of implementing biosecurity measures as well as the costs of not implementing them.

A biosecurity strategy must be evaluated and updated on a regular basis to reflect changes in internal infrastructure, production, and external exposure, as well as regulations. The most effective strategy to establish robust biosecurity at an aquaculture plant is to create a documented biosecurity plan based on risk assessment and utilise audits to determine how well the plan meets the risks and hazards present. The grading method will be critical in determining the relative relevance of the many elements and activities included in the plan, both individually and as part of a biosecurity farm programme. A biosecurity strategy will not be effective unless it is adequately taught and adopted by farm employees as a routine operating procedure. Biosecurity cannot be cost-effective unless farmers collaborate transparently at the regional, national, and international levels. Transparent reporting of critical data and information exchange on the area health status, particularly the prevalence of infectious illnesses and increasing mortality occurrences, is critical. Transparent collaboration among stakeholders is the only way for the industry to effectively prevent and control disease outbreaks ^[55].

5.5. Fish Genetics on Farming

Appearance factors in fish, or those exterior body qualities that impact consumer acceptability at the moment of sale, have risen to prominence in commercial fish farming, as culture success is strongly tied to control of these traits. Body form and skin pigmentation are the two most important physical characteristics. An examination of the genetic basis of these qualities in various fish finds considerable genetic diversity among populations, indicating the possibility of genetic improvement. Work on determining the minor or main genes driving commercial fish aesthetic attributes is growing, with significant success in model fish in terms of discovering genes that regulate body form and skin colors ^[56].

As a result, in order to meet current market expectations and maximize profitability, manufacturers are being obliged to regulate outward features, particularly body form and skin color, more intensely on an industrial scale. In commercial fish, such as common carp, tilapia, sea bream, and salmonids, this genetic strategy is supplemented previous progress based solely on breeding values estimated with phenotypic and genealogical information or classical genetics, which has enabled the development of new strains, for example ^[56][57].

This is not a simple operation, however, because body form and skin colour in fish are complicated features influenced by a variety of hereditary and environmental variables. Thus, development in this subject will be dependent, in part, on unravelling the underlying genetics of these traits in order to use current selection procedures, such as marker-assisted selection based on molecular data, in the future ^[56].

This type of selection approach has resulted in new fish populations with greater market involvement, contributing to better profitability of fish cultures. Because of the sophistication of the market in many parts of the world, this tendency is projected to continue in the coming years. As a result, there is interest in fish selection to ensure visually pleasing species, such as tilapia, rainbow trout, common carp, gilthead sea bream, and sea bass ^[56].

To address this challenge, however, fish producers must adapt and connect their selective breeding objectives with market expectations. One older and antique approach that might be used to attain this goal is the finding of quantitative trait loci (QTLs) or genes that underpin body form and skin colour, where continuous variation of the various qualities that comprise these traits is typically found. This knowledge might be utilized to conduct marker-assisted selection, which is based on molecular markers that are strongly related to QTLs that affect several appearance features of economic relevance. This technique still is widely applied in various countries for the rainbow trout, common carp, gilthead sea bream, and sea bass farming ^[56].

However nowadays, the trend is the selective breeding using genomic selection, which has an enormous potential to increase aquaculture efficiency and minimize its environmental footprint ^[58]. This genomic selection is based in enhanced genomic tools during the last decade. Thus, these genomic tools are extremely useful for the sustainable genetic improvement. Nowadays, these tools have low cost and ease of use, mean that they can now be used at all stages of the domestication and genetic improvement process, from informing the selection of base populations to advanced genomic selection in closed commercial breeding nuclei ^[58][59]. With the high interest in this genetic technology, equipment companies are being interested to develop equipment for the fish farming. Thus, R&D and fishery-related laboratories can sequence a target fish species' genome, eliminating the need for the coordinated effort and financing that resulted in the first farmed animal species' reference genome assemblies (for example the QTLs method) ^[58]. 

Furthermore, genomics technologies are useful for addressing species-specific breeding and production difficulties associated with the very diversified biology of aquaculture species. The introduction of well-managed selective breeding programs for aquaculture based on pedigree recording and routine trait assessments has resulted in increased output of various species (QTLs method). This previous work which can be upgraded with these new genomics technologies can drive the fish farming to a new a level of aquaculture in safety, economic and efficiency levels ^[58].

In conclusion, biotechnological developments have the potential to overcome productivity constraints in aquaculture if the all the work done is coupled with new technologies and not start from the zero.These advancements include the use of genome editing technologies to make targeted changes to aquaculture species' genomes, resulting in improved health and performance, the use of reproductive biotechnologies such as surrogate broodstock to accelerate genetic gain, and combinations of both approaches ^[58].

5.6. Dangers Nowadays in Fish Farming

Finally, Mahamud et al. ^[60] discuss the factors associated with the introduction of macro and microplastics (MPs) in aquaculture, via fishmeal obtained from animals caught in natural environment that can accumulate these materials. There are great consequences of MPs on cultivation ponds, in fish physiology and consumer health. The authors recommend taking necessary care to improve the PM screening process during fish food production and focus on further studies to elucidate the impacts of MPs on sustainable aquaculture production.

Because there are several international and national aquaculture certification systems, the FAO created technical criteria for aquaculture certification as well as an evaluation methodology. However, although many big fish farms are obliged to do environmental impact studies and get certification, small farms, many of which are unsustainable, are not. Many nations have lax regulations managing responsible aquaculture development ^[44].