MEASURING METABOLIC RATE OF EMBRYONIC FISH TO PREDICT GROWTH RATE
Growth and feed efficiency are primary determinants of profit in fish production. Maximizing growth rates minimizes the time to achieve a marketable size and decreases the investment time and expense of rearing slow growing individuals. Feed costs constitute 45-70% of production costs. Thus, selection to improve feed efficiency and growth has the potential robustly increase producer profits. However, since growth and feed acquisition are tightly linked, selection for growth is selection for fish that consume more feed, not fish that are genetically superior for growth. Differences in feed consumed may result from variation in phagic drive or aggression.
The link between metabolic rate and growth is well established across fish species. We have pioneered the application of an AlamarBlue® based assay, to measure metabolic rate in fish and take advantage of the known link between growth and metabolic rate. This assay is amenable to scaling which allows for the simultaneous measure of metabolic rate in thousands of embryonic fish.
We hypothesized that by assessing metabolic rate in embryonic tilapia we could predict growth potential. Metabolic rate, measured by reduction of AlamarBlue® over 16h exposure, was assessed in 6000 embryonic fish/experimental unit resulting in high and low quartiles that included 1500 tilapia. Three replicates of high and low metabolic rate tilapia were reared identically under standard industry conditions at Desert Springs Tilapia (Agua Caliente, AZ). Tilapia in the high metabolic rate group grew more quickly to harvest than tilapia in the low metabolic rate group. In fact, tilapia that had a high metabolic rate was 29% heavier at harvest than tilapia that had a low metabolic rate as embryonic fish (Figure 1; P < 0.05). In a second study conducted in 1 m3 tanks at the University of Arizona, we showed that selection based on metabolic rate could improve feed efficiency and growth. In fact, fish selected as having a high metabolic rate (top 10%) ask yolk-sac fry had a feed efficiency (measured across 5 months) that was 5.1% greater than fish selected to have a low metabolic rate (bottom 10%) as yolk-sac fry (P = 0.03).
Herein, we shown that this assay allows for selection of fish based on metabolic rate as a proxy for the genetic potential for growth. Subsequent studies aimed at understanding the potential application of this assay to improve feed conversion are currently underway. We envision application to select for fast growing individuals or broodstock across aquatic species.