**3.1 Redox balance in feeding strategies**

Usually, the main aim of the diet trials in fish pursue to improve growth performance as well as food conversion and efficiency, guaranteeing a high-quality product, reducing fish mortality and with economic positive gains. Recently, feeding studies include redox balance markers as additional indicators of the fish physiological status. **Table 1** represents the most relevant feeding strategies in Mediterranean fish related to redox balance.


*To enhance the response to handling stress. \*\*To enhance the response to thermal stress.*

#### **Table 1.**

*Last decade works related to feeding strategies in Mediterranean teleost fish.*

#### *3.1.1 Fish oil reduction*

During the last two decades several feeding strategies and economic needs have been promoted the reduction of total protein and the substitution of both fish meal and fish oil for other sources such as vegetable, algae and even insects or yeasts. However, a common strategy for the sector cannot be achieved due to the great variability within the biology of fish species concerning, for instance marine versus freshwaters; carnivorous versus. herbivorous and omnivorous; temperate versus eurytherms, etc.

The replacement of fish oil (FO) by vegetal oil blend (VO) (20% rapeseed, 50% linseed, and 30% palm oils) would promotes lower levels of lipoperoxidation (LPO) products in liver and intestine, together with higher enzymatic activities of GPX and GR in intestine of sea bass, *Dicentrarchus labrax* [32, 33]. When a stressful condition introduced, carbohydrate rich diets also diminished LPO products and increased GR and glucose 6-phosphodihydrogenase (G6PDH) and VO diets enhanced GPX and G6PDH activities [33]. The same diet strategy was conducted in other species such as the gilthead sea bream, *Sparus aurata*, evidencing that the enriched diets with starch carbohydrates promoted the antioxidant defences by reducing oxidized glutathione and lower LPO products [34]. By its way, in common dentex, *Dentex dentex*, higher carbohydrates levels inclusion in diets, increased GPX in liver and white muscle and GR in liver and 18 and 24% and decreased oxidative products as protein carbonylation in liver and LPO in liver and white muscle [35].

In addition to the studies of reducing FO consumption by reducing from VO substitution, some authors had considered that the lipid content of commercial diets must be lowered. Sánchez-Nuño et al. [21] evidenced that the reduction from 18–14% in the lipid content of the diet did not affect *Sparus aurata* growth, glutathione levels or enzyme activities, but did reduce the amount of LPO.

#### *3.1.2 Fish sources reduction in diet formulation*

The substitution (total and partial) of fish meal proteins by vegetable sources (soybean and wheat proteins as the main used products in the last decades) seems to be another relevant topic in diet substitution. Although a classic discrepancy exists on the benefits to substitute protein by carbohydrate and its effects on fish growth, for several fish species the carbohydrate inclusion to replace protein would benefit redox status, and if the growth performance is not affected, this strategy could be considered as beneficious for fish welfare.

In gilthead sea bream [36] fed with formulated diets replacing fish meal by soybean protein at 20, 40 and 60% showed a gradually increase of liver antioxidant enzymes activities (SOD, CAT, GPX, GR) according to higher levels of fish meal replacement. Despite any oxidized products were not evaluated, growth performance and immunity markers were negatively affected, suggesting that fish proteins are essential in diet formulation. However, when soybean diets were supplemented with methionine and phosphate fish redox status enhanced significantly [37]. In the same line, glutamine and arginine supplementation would improve deleterious effects of higher fish meal substitutions [38, 39] although with lower benefits observed with methionine inclusion. Taurine supplementation was also proposed to improve fish welfare when fish meal is replaced by vegetable oils but with not clear benefits [40].

Irrespective to sources substitution several studies approached specific supplements to improve the redox balance to benefit fish welfare. A combination of methionine and white tea dry leaves supplementation to a commercial diet were proposed

**99**

*Redox Balance Affects Fish Welfare*

in **Table 2** and discussed below.

*Dicentrarchus labrax* Liver, intestine,

white and red muscle

*Dicentrarchus labrax* Liver Salinity and ammonia

*Dicentrarchus labrax* White muscle 18 versus 24 versus

**Starvation**

**Handling**

**Salinity**

**Hypoxia**

**Temperature**

amount were evident.

*DOI: http://dx.doi.org/10.5772/intechopen.89842*

in gilthead sea bream by [41]. After 4 weeks feeding this diet liver SOD and CAT activities were increased, although no reduced LPO levels or higher glutathione

**3.2 Redox balance in response to environmental stress conditions**

Another of the most relevant aspects in animal culture is the exposure to continuous environmental stressors and, in the most cases, fish are challenged to various types of abiotic or biotic stressors simultaneously. Whereas in the wildlife, fish have the freedom to migrate to locations where environmental conditions are within their tolerance range or to escape from disfavour ones, in culture conditions their confinement makes the escape impossible and entails the need to face up stressors with physiological responses. The classical abiotic and biotic stressors for fish culture are infections, parasites, changes in water salinity, exposure to dissolved heavy metals, the decrease in oxygen availability, the food access limitation, human handling, higher densities and mainly, at temperate latitudes, the natural and seasonal variations in water temperature. From the last two decades, the implications of physiological redox balance to face up culture conditions stressors are of the main interest for scientists and farmers. Some of the most relevant works are summarized

**Tissue Environmental stress Oxidants Antioxidants**

LPO SOD, CAT, GPX

LPO CAT

LPO, H2O2

G6PDH

SOD, CAT, GR, GPX, GSH and GSSG

G6PDH

Starvation 1–2 months [44]

toxicity [45]

28°C [52]

*Dicentrarchus labrax* Liver, intestine Handling stress [33] LPO SOD, CAT, GR, GPX,

*Sparus aurata* Liver, heart Hypoxia [47] LPO CAT, GR, GPX, GST

*Solea senegalensis* Liver 12 versus 18°C [19] LPO SOD, CAT, GR, GPX,

Other novel techniques and feed strategies were also assayed in fish nourishment studies. For instance, the inclusion of spray-dried plasma from porcine blood (SDPP) has been evaluated because of in mammals evidenced great results in immune and redox status. In fish fed with 3% of SDPP showed lower CAT, GR, and Glutathione S-Transferase (GST) enzymatic activity [42]. Other emerging strategy is to enrich diets with bacterial probiotics and to study its effects also in redox status. A recent study including *Shewanella putrefaciens*, *Pdp11* and *Bacillus* sp. evaluated the gene expression of redox balance markers in gill, intestine and epidermal mucosae [43]. Experimental diets alter the expression of the studied antioxidant genes, primarily in the gill and skin. Furthermore, the tested probiotics and mainly, the palm fruits extracts had significant antioxidant properties especially after feeding for 30 days.

### *Redox Balance Affects Fish Welfare DOI: http://dx.doi.org/10.5772/intechopen.89842*

*Redox*

*3.1.1 Fish oil reduction*

eurytherms, etc.

white muscle [35].

During the last two decades several feeding strategies and economic needs have been promoted the reduction of total protein and the substitution of both fish meal and fish oil for other sources such as vegetable, algae and even insects or yeasts. However, a common strategy for the sector cannot be achieved due to the great variability within the biology of fish species concerning, for instance marine versus freshwaters; carnivorous versus. herbivorous and omnivorous; temperate versus

The replacement of fish oil (FO) by vegetal oil blend (VO) (20% rapeseed, 50% linseed, and 30% palm oils) would promotes lower levels of lipoperoxidation (LPO) products in liver and intestine, together with higher enzymatic activities of GPX and GR in intestine of sea bass, *Dicentrarchus labrax* [32, 33]. When a stressful condition introduced, carbohydrate rich diets also diminished LPO products and increased GR and glucose 6-phosphodihydrogenase (G6PDH) and VO diets enhanced GPX and G6PDH activities [33]. The same diet strategy was conducted in other species such as the gilthead sea bream, *Sparus aurata*, evidencing that the enriched diets with starch carbohydrates promoted the antioxidant defences by reducing oxidized glutathione and lower LPO products [34]. By its way, in common dentex, *Dentex dentex*, higher carbohydrates levels inclusion in diets, increased GPX in liver and white muscle and GR in liver and 18 and 24% and decreased oxidative products as protein carbonylation in liver and LPO in liver and

In addition to the studies of reducing FO consumption by reducing from VO substitution, some authors had considered that the lipid content of commercial diets must be lowered. Sánchez-Nuño et al. [21] evidenced that the reduction from 18–14% in the lipid content of the diet did not affect *Sparus aurata* growth, glutathi-

The substitution (total and partial) of fish meal proteins by vegetable sources (soybean and wheat proteins as the main used products in the last decades) seems to be another relevant topic in diet substitution. Although a classic discrepancy exists on the benefits to substitute protein by carbohydrate and its effects on fish growth, for several fish species the carbohydrate inclusion to replace protein would benefit redox status, and if the growth performance is not affected, this strategy could be

In gilthead sea bream [36] fed with formulated diets replacing fish meal by soybean protein at 20, 40 and 60% showed a gradually increase of liver antioxidant enzymes activities (SOD, CAT, GPX, GR) according to higher levels of fish meal replacement. Despite any oxidized products were not evaluated, growth performance and immunity markers were negatively affected, suggesting that fish proteins are essential in diet formulation. However, when soybean diets were supplemented with methionine and phosphate fish redox status enhanced significantly [37]. In the same line, glutamine and arginine supplementation would improve deleterious effects of higher fish meal substitutions [38, 39] although with lower benefits observed with methionine inclusion. Taurine supplementation was also proposed to improve fish welfare when fish meal is replaced by vegetable oils

Irrespective to sources substitution several studies approached specific supplements to improve the redox balance to benefit fish welfare. A combination of methionine and white tea dry leaves supplementation to a commercial diet were proposed

one levels or enzyme activities, but did reduce the amount of LPO.

*3.1.2 Fish sources reduction in diet formulation*

considered as beneficious for fish welfare.

but with not clear benefits [40].

**98**

in gilthead sea bream by [41]. After 4 weeks feeding this diet liver SOD and CAT activities were increased, although no reduced LPO levels or higher glutathione amount were evident.

Other novel techniques and feed strategies were also assayed in fish nourishment studies. For instance, the inclusion of spray-dried plasma from porcine blood (SDPP) has been evaluated because of in mammals evidenced great results in immune and redox status. In fish fed with 3% of SDPP showed lower CAT, GR, and Glutathione S-Transferase (GST) enzymatic activity [42]. Other emerging strategy is to enrich diets with bacterial probiotics and to study its effects also in redox status. A recent study including *Shewanella putrefaciens*, *Pdp11* and *Bacillus* sp. evaluated the gene expression of redox balance markers in gill, intestine and epidermal mucosae [43]. Experimental diets alter the expression of the studied antioxidant genes, primarily in the gill and skin. Furthermore, the tested probiotics and mainly, the palm fruits extracts had significant antioxidant properties especially after feeding for 30 days.
