Abstract
Due to the implementation of breeding programs, imported rainbow trout have better growth and quality than the rainbow trout propagated in Iran. This compared the meat quality and stress resistance of Spanish imported and Iranian rainbow trout reared in both spring and river water sources. A total of 432 individuals from each breed were subjected to four treatment conditions with three replicates in 12 pools over a 90-day period. At the conclusion of the rearing period, meat quality was assessed through proximate analysis. Additionally, 20 randomly selected fish from each treatment were subjected to acute temperature stress, as well as exposure to acidic and alkaline pH conditions. Our findings reveal no significant differences in carcass protein and fat percentages between Spanish and Iranian trout across both river and spring water sources. The highest protein content was observed in Iranian and Spanish trout reared in river water. Moreover, survival rates of Spanish trout were significantly higher than those of Iranian trout when subjected to temperature stress, acidic pH, and alkaline pH in both spring and river water sources (P<0.05). Overall, our results demonstrate that Spanish rainbow trout exhibit greater resilience to environmental stressors compared to Iranian trout, likely attributed to the implementation of targeted breeding programs in this breed.
 

INTRODUCTION

Despite the widespread interest among rainbow trout farms in using imported fish for cultivation, there is a lack of comprehensive and definitive information regarding the superior growth, survival, and resistance of these strains compared to domestically produced rainbow trout. Limited research conducted in this field in the country has shown that larvae's growth indices and survival rates of Danish imports were superior to domestically produced larvae (Mahdavi et al., 2013). Additionally, Fattahi Tari et al. (2013) revealed that French rainbow trout had a higher protein content than Iranian samples of the same weight. Currently, Spanish eyed eggs are abundantly imported into the country
and cultured in many farms (Mohammadi et al., 2023). It had previously been established that imported Spanish rainbow trout had better growth performance and survival compared to Iranian rainbow trout (Mohammadi et al., 2023). The current study involved conducting approximate analysis tests and environmental stress challenges to compare the carcass quality and resistance to acute temperature and acidic/alkaline pH stressors in Spanish and Iranian rainbow trout raised in spring water and rivers.
 

MATERIALS AND METHODS

During this study, a total of 864 specimens of rainbow trout fry—both domestically bred and imported from Spain (432 specimens of each) —were selected as experimental populations. These specimens, with initial weights of 19 grams for Spanish rainbow trout and 25 grams for Iranian rainbow trout, were stocked in 12 rearing tanks. The experimental treatments comprised four groups of Iranian and Spanish rainbow trout, each reared in two different water sources (spring and river) over a three-month period (90 days) in three replicates.
The approximate composition of the whole body, including moisture, protein, fat, and ash, was evaluated using standard methods recommended by the Association of Official Analytical Chemists (AOAC, 2005). At the end of the feeding period, 20 fish from each treatment were randomly selected and subjected to three stress challenges—temperature stress, acidic pH, and alkaline pH—in two replicates for each stressor. The survival rate of the fish after exposure to stress was assessed and compared.
 

RESULTS

Over the 90-day period, the protein content in the flesh of Spanish and Iranian rainbow trout did not show a significant difference in either the river or spring water sources. However, within Iranian rainbow trout, significantly, higher protein content observed in river compared to spring water (P<0.05). The percentage of carbohydrates in the flesh of Spanish rainbow trout from the river water treatment and Iranian rainbow trout from river water did not show a significant difference (P>0.05).
Spanish rainbow trout showed a 75% survival rate in both spring and river water sources. However, 100% of Iranian rainbow trout in both spring and river water sources were observed to be lethargic, dark in color, and at the water surface after 6 hours of temperature stress and 7 hours of acidic and alkaline pH stress. The survival rate of Spanish rainbow trout in both spring and river water sources against temperature stress, acidic pH, and alkaline pH stressors was significantly higher than that of Iranian rainbow trout in both spring and river water sources (P<0.05).
 

DISCUSSION AND CONCLUSION

The largest exporters of eyed eggs of rainbow trout to Iran include countries such as Spain, Denmark, France, Norway, and the United States. Nevertheless, comprehensive and definitive information comparing the performance of imported cultured fish to those bred in Iran is lacking. Previous studies have shown that imported Spanish rainbow trout exhibit better growth performance and survival compared to Iranian rainbow trout (Mohammadi et al., 2023). In the current study, the meat quality and resistance to acute temperature and pH stressors in Spanish and Iranian rainbow trout raised in two different water sources, spring and river, were examined and compared.
The results did not reveal significant differences in the flesh analysis between Spanish and Iranian rainbow trout. However, the carcass protein content in Iranian rainbow trout was significantly higher in river water compared to spring water, which may be due to temperature and water quality differences in these two water sources.
Environmental stresses, including temperature and pH stresses, particularly in intensive fish farms, can lead to reduced growth performance, health issues, and fish mortality. According to a study by Wagner et al. (1997), high temperature stress combined with high pH significantly contributed to fish mortality in rainbow trout. The current research indicated that the survival rate of Spanish rainbow trout in both spring and river water sources against temperature stress, acidic pH, and alkaline pH stressors was significantly higher than that of Iranian rainbow trout. This suggests that the breeding improvement in Spanish rainbow trout likely contributed to enhanced resistance against environmental stressors. These findings align with the better growth0 performance of Spanish rainbow trout compared to Iranian rainbow trout (Mohammadi et al., 2023).
In conclusion, this study demonstrated that Spanish rainbow trout exhibited greater resilience against environmental stressors compared to Iranian rainbow trout. Additionally, considering the better growth and survival of imported Spanish rainbow trout compared to Iranian ones, it can be inferred that the better performance of Spanish rainbow trout is due to the implementation of breeding improvement programs in this species.
 
REFRENCES
AOAC., 2005. Official methods of analysis. 18th ed., Gaithersburg, MD: Association of official analytical chemists. Aquaculture, (224), pp. 283-299.
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Mahdavi, M., Majazi Amiri, B., Sayad Borani, M., 2013. Comparison of hatching percentage, survival and growth of rainbow trout (Oncorhynchus mykiss) larvae obtained from imported and domestic hatched eggs. Aquaculture Development Journal, 7(1), pp. 87-94. 6012813920108.pdf. (In Persian)
Mohammadi, A., Abdoli, L. and Akbarzadeh, A., 2023. The comparison of growth parameters of Iranian and imported Spanish strains of rainbow trout (Oncorhynchus mykiss) reared in two water sources of river and spring. Journal of Fisheries Science and Technology, 12(2), pp. 100-111. http://dorl.net/dor/20.1001.1.23225513.1402.12.2.1.7 (In Persian).
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