Feed & Additive Magazine Issue 3 April 2021

SPECIAL STORY 66 FEED & ADDITIVE MAGAZINE April 2021 when water activity is high. Mycotoxins are extremely stable to physiochemical treat- ments and their presence in the crops with- out proper mitigation leads directly to their consumption by the farmed animals, im- pacting health and production. These negative effects in aquatic species range from acute mortality to chronic re- duction in immunity, fecundity and per- formance, these are becoming even more pronounced once the animal is facing ad- ditional biological (e.g. pathogen) or envi- ronmental stressors, the latter of which is primarily climate driven. CLIMATE & DISEASE Climate is not just determining envi- ronmental conditions, it is also implicated in disease. For example, the Brazilian ti- lapia industry is fighting two major dis- eases. In the winter months, francisellosis, caused by Francisella spp., is particularly problematic, whilst in the summer months the main challenge comes from Streptococcus spp. (causing streptococcosis). Since the etiological agents are defined by differ- ent characteristics, in this case Gram-negative vs Gram-positive bacteria, producers must use differ- ent management strategies to control their impact. From experience, it is evident that organic acids can combat better Gram-negative pathogens (Figure 1), whilst phytogenic feed additives may be more effec- tive against Gram-positive bacterial threats (Figure 2). A similar temperature effect can be seen for other pathogen types, for example white spot syndrome vi- rus (WSSV) in shrimp appears to be more serious in temperatures below 30°C rather above 30°C. Rainfall can also have a great impact in shrimp cul- ture; increased rainfall will lead to a reduction in sa- linity, whilst a lack of rainfall may lead to increase in salinity, especially in combination with hot weather where evaporation is high. Since Vibrio spp. are af- fected by salt concentration, it follows that fluctuating salinity may affect their abundance, not to mention impacting shrimp ability to osmoregulate effectively. Although it is not clear how climate change will affect the biology of commercially important aqua species, it is certain that climate change will have an impact on aquaculture. But in some ways, aquaculture may be capable of mitigating some of the negative effects. Figure 1. Survival of tilapia after Aeromonas hydrophila challenge with and without an enhanced organic acid. Source: BIOMIN Figure 2. Survival of tilapia after Streptococcus agalactiae challenge with and without a phytogenic feed additive. Source: BIOMIN