Abstract

  https://doi.org/10.1007/978-3-030-05603-2_7

The primary basis for the concept of “animal welfare” is the belief that animals are sentient being capable to experience good or bad feelings or emotional states. Stress and stress-related responses should be considered as an adaptive condition of the organism that has the fundamental function of preserving the individual’s life. However, determination of animal welfare requires the selection, collection and interpretation of different parameters and validated indicators. The aspects of the fish’s condition that are often used in this context are its health status, its physiology and its behaviour.
According to the EU organic regulation, livestock farming and aquaculture should respect high animal welfare standards and meet animals’ species-specific behavioural needs, while animal-health management should be based on disease prevention. In this respect, particular attention should be paid to housing conditions, husbandry practices and stocking densities.
Indeed, farmed fish are exposed to a range of industry practices that may act as chronic stressors which potentially compromise welfare. The effects of a wide range of aquaculture practices on the stress physiology of fish are well documented, and include frequent handling, transport, periods of food deprivation, deteriorating water quality, sub-optimal stocking densities, fin-clips and environmental enrichment.
The waste derived from fish feed and its metabolic end products, such as uneaten feed, faeces and excretions and dissolved inorganic nutrients, can seriously impair water quality and can cause stress, reduced growth and increased incidence of diseases to the point to be lethal for fish themselves. Thus, monitoring chemical and physical parameters, such as concentration of dissolved oxygen, carbon dioxide, un-ionized ammonia-nitrogen, nitrite-nitrogen, pH, nitrate concentration alkalinity and temperature, is essential to ensure optimum water quality.
It is very difficult to make generalizations about how stocking density affects welfare in all situations, because a great interspecific variability could be associated with the responses to this factor. Nevertheless, high rearing densities induce in many teleost the increase of the energetic expenditure for basal life functions, which in turn could become detrimental for growth and immune resistance, and could also affect the social interaction between fish.
The preventive practices, as well as the use of nonantibiotic and environmentally friendly agents, are one of the key factors for health management in organic aquaculture. In recent years, probiotics have taken a central role and represent an unconventional approach that has numerous beneficial effects in fish and shellfish culture, such as improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. The concept of biological disease control, particularly using microbiological modulators for disease prevention, has received widespread attention. Probiotics thus are opening a new era in the health management strategy from human to aquatic species including fish and shellfish.