INDIRECT CRITERIA TO SELECT THE RAINBOW TROUT LINES TO ENHANCE THE EFFICIENCY OF SOYBEAN MEAL UTILIZATION IN THEIR DIET

We have developed several rainbow trout (Oncorhynchus mykiss ) lines  that show higher growth rates when fed all plant protein diet than non-selected lines of trout  fed a fishmeal-based diet . So far, no commercial breeding programs has yet started to improve feed utilization efficiency in fish, mainly because of the difficulty in accurately measuring individual feed intake of fish reared in groups. W e propose to test if feed intake and body weight variations  during successive periods of feed deprivation (FD) and re-feeding (RF)  are correlated using compensatory feeding regime with trout for genetic improvement of plant protein-based diets (PPB D) utilization using indirect selection, and to develop alternative criteria to improve feed intake of PPBD in fish.

We have used 1600 fish (av. int. wt. 30 g) from 12 families of the selected line  fed plant protein (50% soy) diet (protein: 41% and lipid: 21%) .  Firstly, fish were tagged individually reared in common environment, fish were  on 1st feeding challenge for 4 months (one month each challenge either FD or RF) , and  growth performance were recorded. Thereafter, f ish were separated into four groups (1331 fish)  based on individual performance during FD and RF challenge studies (Fig 1A) . Re sidual Feed Intake (RFI) was recorded for 3 months in all four groups followed by measuring the stability of  response to  the FD and RF periods (2nd feeding challenge for 4 months) which was the same as the 1st feeding challenge. Out of 1331 fish, 143 fish exhibited a similar pattern of weight loss and gain, confirming the  performance stability (Fig 1B) .  We have selected those individual fish (different families , Fig 1C) for spawning to challenge their offspring with PPB.

Conclusively, we have achieved the goal to select trout lines for best feed efficiency. In addition, our aim is to understand the underlying molecular mechanism on how some fish can conserve energy more efficiently compared to others and loose less weight over a FD period and gain more weight  over a RF period (Fig. 1).  To achieve this goal the expression pattern of the genes involved in growth, proteolysis and electron transport chain as  well as the gut microbiome are being studied .  At the end of genetic selection, feed (soy based) efficiency  will be improved  by 10-20% per generation which means  feed cost  will be decreased for sustainable for fish farming.