2012 Annual Report
1a.Objectives (from AD-416):
The objective of this research is to improve the competitiveness of rainbow trout production by reducing feed costs through the development of improved ingredients, feeds, and strains of rainbow trout.
1b.Approach (from AD-416):
Ingredients will be selected based upon nutrient and anti-nutrient profiles, and cost on a protein unit basis. Special emphasis will be placed upon barley and oat cultivars, but any ingredient that has favorable profiles will be considered. Some marine oils and proteins maybe evaluated at low inclusion levels to enhance feed palatability and the final product fatty acid profile. Practical feed formulations, will be produced using cooking extrusion (commercial conditions) for rapidly growing juvenile fish. Traditional evaluation procedures, including growth performance and nutrient retention, and cost per unit gain, will be used to evaluate the improved diet formulations. Additional evaluation procedures will be developed and applied to fish feeding trials as follows: (1) clinical assays of blood plasma for electrolyte levels, cholesterol, triglycerides, ASAT, ALAT, and routine plasma parameters; (2) whole blood analysis for hematocrit percentages; (3) gene expression activities for genes associated with protein synthesis and degredation, fatty acid elongation and desaturation, bone and/or cartilage metabolism and energy metabolism plus cellular redox status. Reproductive performance of rainbow trout fed diets containing plant-derived ingredients in place of fishmeal and fish oil (partial replacement or total replacement for selected growth periods) will be assessed by measuring fecundity, egg fertility, and egg hatchability, plus chemical analysis of eggs to determine effects of diet on nutritional content. Bone density and imaging may be explored for fish fed diets lacking fishmeal to determine if replacement mineral supplements in plant-based feeds support normal bone development and absence of skeletal deformities.
The collaborative research between ARS and UI focused on three key tasks:.
1)Identify rainbow trout families with improved phenotypes for growth and utilization of a grain-based fish feed through a genetic selection program, begin to assess performance of selected families as triploid fish and begin to establish sex-reversed broodstock to produce all-female populations, the primary types of rainbow trout used in commercial production.
2)Conduct feeding trials to evaluate nutritional value of grain-based products.
3)Conduct feeding trials in support of the goal of developing a commercial trout feed based on oilseed and grain products without inclusion of marine protein and/or oil.
Each of these tasks apply to the Parent Project Objective 3: Determine nutritional value of alternative ingredients (protein, lipid, energy) and develop practical feed formulations for improved strains of fish, Objective 4: Determine optimal nutrient supplementation levels for specific life stages of improved strains of trout, Objective 5: Use gene expression analyses to advance the understanding of gene targets for improving nutrition, growth, and development processes under production conditions, or Objective 6: Identify phenotypic differences in rainbow trout for growth and utilization of plant-based sustainable diets and determine the genetic variation for the identified traits.
For Task 1, 160 single family crosses were made using rainbow trout families in fall 2011 and evaluated for performance when fed an all plant protein diet. Eggs, fry and fingerlings from the crosses were incubated and reared separately over a period of 7-8 months to maintain cross identity. Performance of family cross groups fed the plant protein diet was compared to that of cohorts fed a conventional fishmeal-based diet. After evaluation of performance and upon reaching approximately 200g in average weight, the top 40 families were identified and the top 15 fish from each of the top families were marked with a PIT tag and pooled in several outdoor raceways for communal rearing to maturation in fall of 2013. Meanwhile, tagged fish from the previous year class were communally reared and will spawn in fall 2012. A pressure chamber was purchased to induce triploidy in rainbow trout eggs soon after fertilization. However, the chamber did not arrive until late in the spawning period. Attempts to induce triploidy by high pressure were unsuccessful due to failure of the steel frame upon which the pressure chamber was mounted. A replacement frame of higher quality was purchased but arrived after the spawning season had ended. Triploidy will be induced in eggs from the 2012 spawning. Approval was obtained to begin sex-reversed broodstock development from selected trout families.
For Task 2, a 12-week feeding trial was completed with post-juvenile rainbow trout fed either a fishmeal-based or all plant-product diets supplemented various levels of zinc, supplied as zinc sulfate. Plant-based trout feeds contain lower baseline levels of zinc than do fishmeal-based feed and further contain phytic acid, a potential zinc antagonist that reduces zinc digestibility. Fish weight gain increased with zinc supplementation up to 30 ppm but no significant differences associated with dietary zinc supplementation were observed in weight gain of fish fed the fishmeal-based diet. Other response variables, such as gene expression and tissue histology, are being assessed.
For Task 3, a 16-week feeding trial was completed with juvenile rainbow trout (initial average weight 3 g) fed experimental diets lacking fish meal (and therefore residual fish oil containing omega-3 fatty acids) and containing varying amounts of Alaska fish oil and canola oil to achieve 0.20, 0.34, 0.48, 0.62, 0.76 and 0.92% long-chain, polyunsaturated omega-3 fatty acids. The purpose of the study was to determine the minimum amount of fish oil needed in young trout to support normal growth and health. After 16 weeks of feeding and a 65x increase in initial fish weight, no clinical signs of omega-3 fatty acid deficiency were observed. Trout fed diets containing 0.34-0.92% omega-3 fatty acids did not differ in final fish weight (~178-215 g), but the average weight of fish fed the lowest level of dietary omega-3 fatty acids was significantly different from that of trout fed the highest dietary level (158 g). Fatty acid analysis of fish samples did not indicated abnormal levels of indicators of omega-3 fatty acid deficiency. Because no plateau in final fish weight was achieved, a follow-up study was initiated that included dietary omega-3 levels up to 1.5% of the diet. This study has been underway for 18 weeks. Average fish weight reached a plateau at 1.25% omega-3 fatty acids in the diet. As observed in the first study, fish fed the diet containing the lowest level of omega-3 fatty acids gained less weight but otherwise appeared normal with no signs of clinical deficiency. This study will continue to 24 weeks of feeding. The initial results of these studies indicate a requirement of rainbow trout for omega-3 fatty acids of about 1.2% of the diet, but this value may change after tissue fatty analysis and gene expression data are considered.