Combined effects of water quality and stocking density on welfare and growth of rainbow trout (Oncorhynchus mykiss)

Abstract

An 84-day experiment assessed the combined effects of two fresh water quality levels (H: 1.71 ± 0.15 mg O 2 l −1 and 0.28 ± 0.01 mg l −1 total ammonia nitrogen (T-AN), L: 5.15 ± 0.07 mg O 2 l −1 and 0.54 ± 0.01 mg T-AN l −1 ) and 3 stabilized stocking densities: 24.8 ± 0.2, 74.2 ± 0.5 and 120.0 ± 0.9 kg m −3 ) on rainbow trout. Fish were fed using demand feeders with rewards proportional to stocking density. Mass increase was significantly affected by water quality and stocking density, being highest in H water and the lowest at 120 kg m −3 . There was no significant difference in final weight between 25 and 74 kg m −3 , but at 120 kg m −3 it was 27% and 19% lower in H and L water respectively than at 25 kg m −3 . Feed intake (FI) from day 0-85 was significantly affected by water quality, 1.5% in H compared to 1.1-1.0 in L, but there were no significant differences in apparent feed conversion (AFC). FI was not significantly affected by stocking density but AFC was impaired, it increased with stocking density. Marked changes in fish morphology and composition were related to water quality: Condition K factor and fillet fat content were significantly higher in H than in L groups. Dorsal and pectoral fin condition was affected by stocking density and water quality: fins were significantly longer and less eroded in L groups and at low stocking density. Physiological measures were within the usual ranges, but differed between treatments. Changes in plasma osmolarity, hydromineral balance (Na + ) and acid base balance (HCO −3 ) showed that fish were more affected by water quality than by stocking density. There was no sign of acute stress in acclimated fish as cortisol and glycemia were similar under all experimental conditions. This study highlights the importance of water quality and feeding conditions when considering the effects of stocking density on fish welfare.

Fish Welfare in Aquaponic Systems: Its Relation to Water Quality with an Emphasis on Feed and Faeces—A Review

“…Sudden changes in the fish stocking density, growth rate, feeding rate or water volume can elicit rapid changes in water quality; hence, regular measurement of those critical water quality parameters is essential. The deterioration of water quality parameters affects fish physiology, growth rate, and feed efficiency, leading to pathological changes and even mortality under extreme conditions [4,5]. In terms of aquaponic systems and considering the fish welfare issues, carrying capacity is of major concern for maintaining the balance between plant and fish requirements in a co-culture medium.…”

“…Carrying capacity expresses the maximum biomass of fish in the system with acceptable water quality limits. The carrying capacity of a given amount of water is determined by the oxygen consumption rate of the fish and their responses to ammonia, CO 2 and other potentially toxic metabolic wastes that are produced [5]. Stress involves a series of physiological and behavioural reactions that help fish resist death or adapt to changing conditions.…”

Sustained swimming mitigates stress in juvenile Brycon amazonicus reared in high stocking densities

“…This index was greater in all fish subjected to exercise, independently of the stocking density, probably because sedentary fish under high densities spend more energy to cope with crowding stress. The combined effects of water quality and high stocking densities also reduced the values of the K of rainbow trout due to low water quality and feeding conditions, causing alterations to fish welfare (Person-Le Ruyet et al, 2008). In the present study, the sharing of the food pellets and the water quality were improved, and the aggressive behavior was reduced, sparing energy for the anabolic processes.…”

Factors Affecting Fin Damage of Farmed Rainbow Trout

“…The regression analysis showed that SD was not a significant predictor in every examined fin model (Table 4 -Table 10). Fin damage is historically linked to SD (3) and the main approach was that higher densities will increase the level of fin damage (26)(27)(28)(29)(30)(31). In our study, SD was the only factor that did not have an effect on the level of fin damage.…”

“…Routine handling affects the level of fin damage as fish come into physical contact with surfaces (nets, grading equipment, vaccination tables) and with other fish during crowding within the rearing units prior to vaccination, grading and processing (3,30,38). In our study, GR received the strongest weight in the model only for the dorsal fin, but higher levels of GR predicted the damage of the dorsal, caudal, anal and left pelvic fin.…”