Disease prevention is a primary and cost-effective method in fish health management. It is more effective and economical than attempting to stop a disease that has already set in. Preventive measures have always big advantage over curative practices. Moreover, the drug may not provide remedies under all circumstances. Also, the drug may not help the host survive the infection until the environment is improved. Ideally, fish culturists should strive to decrease the stress-causing factors and eliminate and prevent the entry of pathogenic organisms by strictly adhering to the fish health monitoring programme.

Histology is an important tool in fish disease diagnosis as it affords the comparison of normal structures or morphology of tissues against those from diseased fish. However, correct diagnosis and confirmation of changes associated with diseases require proper specimen processing and some degree of expertise in histopathology. The four basic types of tissues are: epithelial, connective, muscular and nervous. An organ is usually a combination of these four tissue types. It is important to remember that the histology or structure of an organ is always related to the function it performs.

Diagnosis of nutritional diseases is difficult because many signs exhibited by fish are non-specific and most nutritional deficiencies are hard to define. A compilation of data on feed composition and feeding management, as well as husbandry practices, are needed to define a case. Most of data on fish and shrimp nutritional diseases were gathered under experimental conditions. Under farm conditions, most of that definition would be clouded with errors in husbandry practices or secondary infection. Therefore, attempts to diagnose nutritional diseases should be carefully done using every available technique to define the case.

Outbreaks of viral infections can cause massive mortalities among cultured fishes or shrimps. Water temperature and age of the fish or shrimps are significant factors that influence the development of viral infections. Most fish viral infections occur at low water temperatures, hence, very few viral infections among fishes in warm water culture systems are reported. In addition, most viral infections occur among fry or fingerlings often causing severe mortalities, while older fish or shrimp develop resistance or are hardly affected. Stress from handling, poor water quality, high stocking density and poor nutrition also affect the severity of viral infections. Finally, aquaculturists should beware in importing non-indigenous fish or shrimps into the country as these are potential carriers of viral pathogens.

Over the past 20 years, aquatic animal mycopathogens have become the focus of considerable research. The many known occurrences of fungal diseases in wild populations and the documented devastating disease outbreaks indicate that fungal and fungal-like pathogens are important in nature. Fungal diseases can act as major limitations on natural and cultured populations of aquatic animals. However, knowledge on fungal diseases is rudimentary consisting primarily of the identification and pathology of etiological agents. Detection of fungal infections relies only on the observation of gross pathology, histological examinations, and standard mycological isolation and identification procedures. As a result, there are some cases where the implicated fungal pathogen cannot be demonstrated as the primary cause of a particular disease. In such cases, the fungal pathogen is usually regarded as secondary invader. Continued research in basic mycology is still an essential resource for fish pathologists in diagnosing diseases caused by fungi. Although fungi reportedly affect very few species, fungal diseases, if not properly controlled or prevented, can still pose a threat to the aquaculture industry.

Disease occurrence is one of the biggest deterrents to sustainable production in aquaculture. It is therefore important to enhance awareness among various sectors of the importance of health management in the aquaculture industry. This can be done through education and information dissemination. Students in fisheries and veterinary medicine need to have adequate background information on the aquatic animal disease and health management to understand the problems and needs of a fast-growing aquaculture industry. Recognizing disease signs early and using mortality pattern as a clue to the disease agent involved will not only make diagnosis easier, but it will also prevent massive losses by timely implementation of remedial measures.

Information on the sensory basis of shrimp feeding provides the means for assessment of the effectiveness of food items in terms of smell, taste, size, and colour. This chapter summarizes information about the sensory basis of the feeding behaviour of the giant freshwater prawn (Macrobrachium rosenbergii) and the marine whiteleg shrimp (Litopenaeus vannamei). Existing literature on these shrimp species and other decapod crustaceans is reviewed, and unpublished experiments using the selective sensory ablation technique to determine the involvement of vision, chemoreception, and touch sense in the feeding behavior of the juveniles of M. rosenbergii and L. vannamei are also described. To determine the role of vision in feeding, the eyes of the juveniles were painted over (deprived of vision) with white manicure and their feeding response to commercial pellets was compared with those with untreated eyes. The untreated eyed juveniles detected and approached a feed pellet right away, but the specimens blinded by the coating detected a pellet only after random accidental touch with the walking legs while roaming on the aquarium bottom. Juveniles that had learned to feed on pellets showed food search and manipulation responses to a pellet-like pebble without smell and taste. The early larvae (zoeae) of M. rosenbergii already have colour vision (that likely persists through life) and colour preference for blue and white. The adults of L. vannamei discriminated a blue-colored well among seven grey wells in a palette, also showing colour vision in this shrimp. A behavioural experiment with dyed prawn flesh showed that L. vannamei has innate color preference for yellow food over black, red, green, and blue food regardless of the background colours of the aquarium bottom. To disrupt chemoreception, the juveniles of both the species were abruptly transferred to water of drastically different salinity and the osmotic ablation destroyed the chemosensitive sensilla. The osmotically ablated juveniles approached a pellet right away but failed to ingest it; they had learned the visual cue and texture of the pellets and recognized them by vision and tactile sense. To determine the role of sensory appendages in feeding of L. vannamei juveniles, the antennal flagella, antennular flagella, and the pincers of the pereiopods were ablated. The ablated juveniles roamed the bottom, touched a pellet at random, grabbed it with the maxillipeds, and ingested it. Subsequently they learned to lower the head, actively swim forward, sweep the bottom with the maxillipeds, detect a pellet, and ingest it—thus indicating a plasticity in feeding behaviour in L. vannamei.

Feeding trials were conducted to determine the optimum partial replacement level of soybean meal (SBM) with fermented copra meal (FCM). Isonitrogenous and isocaloric diets containing 0, 5, 10, 15, 20, and 25% of the locally produced FCM partially replacing SBM protein by 0, 12, 27, 41, 56, and 71%, respectively and fully replacing copra meal were formulated. The diets were fed to the fish with an initial weight of 2.83±0.14 g for 12 weeks. Thereafter, the best diet was further tested in a preliminary feeding trial in brackishwater grow-out ponds to verify the performance of the formulated diet against a commercial milkfish feed in an outdoor grow-out system. The results of the indoor tank feeding trial indicated that weight gain of the fish was significantly better in the group fed diet 2, with 5% dietary FCM but further increase in the FCM inclusion level up to 20% of the diet did not exhibit statistical differences against the control. Moreover in the preliminary pond feeding trial, growth and feed conversion ratio (FCR) of the fish fed the FCM diet were significantly higher than the commercial control diet. Survival and nutrient composition of the fish carcass were not adversely affected by the treatments. Hence, optimum dietary FCM inclusion level was determined at 5% of the milkfish diet replacing 100% copra meal and 12% SBM protein. However, in terms of economics, up to 20% FCM can be included in the diet replacing 56% SBM protein may be possible with growth comparable to the FCM-less control.

The escalating aquaculture production from Southeast Asia during the past decades seems inevitable notwithstanding its significant contribution to economic growth and guaranteed food security of the countries in the region. Despite its good prospects, the region’s aquaculture sector is being confronted with various issues that should be addressed to enable it to develop sustainably and contribute unceasingly to poverty alleviation in the region. Responsible aquaculture has been practiced in the region as means of easing the crisis in capture fisheries; however, this has to be matched with effective approaches that address concerns on the fishery resources that are deteriorating. Resource enhancement of economically important aquatic species has been considered as one of the effective approaches that would help protect and restore the aquatic resource habitats and stocks, the latter connotes stock enhancement. As could be gleaned from the current scenario of fisheries in the Southeast Asian region, the recurring over-exploitation of common natural resources has affected the livelihoods of fishers and coastal communities. The imbalanced extraction of natural aquatic resources and natural recruitment has worsened through the years and if left unabated could result in the extinction of many of the region’s endemic aquatic species. It is for such consequences that the Aquaculture Department of the Southeast Asian Fisheries Development Center, while intensifying its efforts in developing sustainable aquaculture, is also promoting resource enhancement as these two approaches are expected to enhance the region’s fishery resources and food security in view of their perfect roles in improving the productivity of aquatic stocks and status of the natural habitats. Nonetheless, aquaculture techniques have always been used to facilitate the stock enhancement of commercially important, threatened and endangered aquatic species. The National Oceanic and Atmospheric Administration of the USA defines stock enhancement as “restoration aquaculture” or the release of hatchery-bred juveniles of fish and shellfish to the wild, and considers this approach as a management tool to recover depleted stocks due to overfishing and habitat loss. The Food and Agriculture Organization of the United Nations has demonstrated that stock enhancement is a type of culture based fisheries since part of the life cycle of certain aquatic species is being controlled in hatcheries before the seeds or juveniles are transplanted or released into open waters — freshwater or brackishwater or marine environments — and allowed to propagate or grow on natural foods until reaching harvestable size.

Micropropagation has proven to be a reliable method to mass produce certain crops. This method also has been applied in macroalgae to produce clones for seaweed farming. Protocols for callus production and shoot regeneration from protoplasts have been established for some seaweed species like Kappaphycus alvarezii. Cells and larger tissues, whether in solid or suspension medium, have been used to propagate clones which were later tested for suitability for farming. Although clonal production was successful, the long duration of culture in vitro limits the production process making the growing of Kappaphycus in vitro an expensive technique to produce clones. In this study, K. alvarezii was grown in vitro to develop a more efficient protocol for the production of clones. Small sections of Kappaphycus were grown in suspension for 1 month under the same temperature, light, and salinity. The type of media, source of explants, length of explants, and stocking density that resulted in the highest growth rate and survival rate were determined. Growth rate of K. alvarezii is significantly higher in media with inorganic nitrogen added than in Grund medium or Ascophyllum nodosum medium only. The appearance of shoot primordia as early as 5 days was observed in media with higher nitrogen concentration. Growth rates of explants approximately 3 and 5 mm are significantly higher than 10 mm sections. Shoots develop significantly faster in explants from tips than sections from older branches. Growth rate of K. alvarezii grown at 0.5, 0.75, 1, 1.25 s 10 mL⁻¹ of medium is not significantly different. This protocol could significantly reduce the (1) time of culture and (2) cost of plantlets production by not using plant growth regulators and formulated media in vitro. Nursery reared plantlets/propagules for farming would be affordable to the stakeholders for sustainability of seaweed production.