Probiotic Applications in Temperate and Warm Water Fish Species - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 254

antibiotics as growth promoters (AGPs) has been a challenge and has increased pressure to find
alternative methods to control and prevent pathogenic bacterial colonization. In fact, farmed
fish are often subjected to environmental stressors (handling, overcrowding, challenging diets
etc.) which may cause an imbalance in the intestinal ecosystem and could be a risk factor for
pathogen infections. Probiotics are live microorganisms added to feed or rearing water that,
when administered to fish in adequate amounts, confer increased viability, enhanced immu-
nity and greater disease resistance. In addition, a possible role of probiotics on fish growth
performance has been supported by recent studies suggesting that the use of bacterial probi-
otics in aquaculture is able to enhance growth through a positive modulation of the insulin-like
growth factor (IGF) system associated with a general decrease of myostatin gene expression
and lower cortisol levels (Carnevali et al . 2006; Avella et al . 2010a; 2011; 2012). As described
by Waché and collaborators (2006), the use of probiotics may improve growth performance
not only due to their beneficial effects on the digestive processes but also by improving stress
tolerance (Rollo et al . 2006). Chronic and acute stress has negative impacts on the immune
system, increasing the susceptibility of fish to infectious diseases.
Disease outbreaks resulting in high mortality rates during the rearing of fish larvae and
unpredictable production of juveniles constitute major obstacles for further expansion of the
aquaculture industry (Toranzo and Barja 1990; Bloch and Larsen 1993; Novoa etal . 1993; Zor-
rilla et al . 1999; Hellberg et al . 2002; Ucko et al . 2004; Johansen et al . 2004; Arijo et al . 2005;
Nishizawa et al . 2006). One of the main beneficial characteristics of probiotics is the ability to
inhibit pathogenic bacteria both invitro and invivo through several different mechanisms such
as competitive exclusion (Moriarty 1997; Gomez-Gil et al . 2000; Balcázar et al . 2004; Vine
et al . 2004), antiviral activities (Kamei et al . 1988; Girones et al . 1989; Direkbusarakom et al .
1998) and host immunomodulation (Picchietti et al . 2007; 2009). Recent literature demon-
strates that probiotics, after sufficient administration, are able to colonize and multiply in the
gut of the host and execute numerous beneficial effects by modulating various biological sys-
tems in the host (Nayak 2010; Merrifield et al . 2010a; Dimitroglou et al . 2011). In particular
the main effects of these feed additives are the improved resistance to pathogenic bacteria col-
onization and enhanced host mucosal immunity, thus resulting in a reduced pathogen load,
an improved health status of the animals and a reduced risk of pathogen translocation via
the gastrointestinal (GI) tract. In particular, concerning their potency to modulate the immune
system, it is widely known that different probiotics, applied as either monospecies or multi-
species, can elevate phagocytic, lysozyme, complement and respiratory burst activity as well as
the expression of various cytokines in fish (Nayak 2010; Merrifield et al . 2010a; Dimitroglou
et al . 2011). Likewise, probiotics can stimulate the GI immune system of fish with a marked
increase in the number of intestinal Ig + cells, acidophilic granulocytes and T cells (Picchietti
et al . 2007; 2009) and stimulation of intestinal pro-inflammatory cytokine gene expression
(Liu et al . 2013; Standen et al . 2013).
These aspects will be reported for important temperate and warm water species in this
chapter. Ichthyologists often group fish species into cold, temperate and warm water groups.
This tends to be a rather arbitrary classification because seasonality, habitat range and
migration patterns dictate that many fish species fall into more than one of these categories.
Indeed, warm water and temperate water fish can tolerate a wide temperature range but
they usually have a minimum temperature requirement for reproduction (ca. 20 ∘ Cfor
many species) and optimal growth is typically above 20 ∘ C, with poor growth or arrested
growth below 10-15 ∘ C (FAO 1989). In order to provide a systematic overview of probiotic