EFFECT OF DIETARY LIPID ON EGG PRODUCTION AND FRY QUALITY OF FATHEAD MINNOWS (PIMEPHALES PROMELAS)

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1 EFFECT OF DIETARY LIPID ON EGG PRODUCTION AND FRY QUALITY OF FATHEAD MINNOWS (PIMEPHALES PROMELAS) Rebecca Lochmann, Nathan Stone, Melinda Bodary, and Harold Phillips University of Arkansas at Pine Bluff

2 Baitfish - Top producer is Arkansas (Estimated value of 37.5 Million in 1998) Fathead minnow Rosy Red Variety

3 INTRODUCTION Spawning of baitfish in captivity is variable and hard to predict Industry leaders are adopting methods that increase their control over spawning conditions - primarily indoor systems There are no diets for baitfish formulated specifically to enhance reproduction or egg & fry number and quality

4 Fry Transfer Method Results: Egg hatching rate of <40% due to predation, fungus and low dissolved oxygen

5 Solution: Spawning and Hatching in Indoor Tanks Benefits: Significantly increased egg survival; Year-round supply of eggs and fry

6 ARE CURRENT FEEDS USED FOR BAITFISH BROODSTOCK NUTRITIONALLY ADEQUATE? Expect protein and energy needs to be between those of fry and fingerlings. A diet with 36% protein (good quality) and 13% lipid (with appropriate EFA s) should suffice.

7 SPECIAL CONSIDERATIONS FOR BROODSTOCK FEEDS - LIPIDS Lipid Quality: The right balance of EFA s is needed. Specific fatty acids (20:4n-3, 20:5n-3 and 22:6n-3) are important for reproduction in many fish. 20:4n-6 is known to affect steroid hormones in goldfish and courtship behavior in fathead minnows.

8 Nutrient Requirements for Reproduction Are phospholipids beneficial? In young fish of some species PL s improve growth, survival and enhance lipid digestibility and transport

9 Compare total egg production (#), egg diameter, fry length and stress resistance of fry from parents fed diets differing in lipid content OBJECTIVE

10 METHODS Approximately yr-old fathead broodstock were stocked into each of 0.59 m 3 outdoor pools in late February- fish were randomly selected - gender could not be determined by external examination in many cases Average weight of female broodstock just prior to spawning was 1.5 g Fish were fed one of 4 diets at 2% bw once daily (Six pools per diet)

11 Composition of the Basal Diet Ingredient (%) Fish meal 10 Soybean meal 52 Wheat bran 17 Corn 8 Vitamin premix 1 Mineral premix 1 Lipid 10 Diets also contained ethoxyquin ( g) & cellulose ( g); 34% protein; Energy:protein ratio of 10.2 kcal/g protein

12 Dietary Lipids Lipid Source(s) Lipid Amount Soybean oil (SBO) 10% Cod liver oil (CLO) 10% SBO + CLO 5% + 5 % SBO + Soy Lecithin 5% + 5 %

13 METHODS After diets were fed to fish for 2 months and showed signs of spawning activity, spawning mats were added to each pool. All eggs were collected from snowed mats over a 4-day period about every 2 wks from April 22 To July 5

14 Eggs were removed from mats, counted, & subsamples were put into a hatching system After hatch, fry were taken to the lab for measurements and stress tests METHODS

15 METHODS Egg #, diameter, and fry length were determined using an ICAS system with a Cool Snap Camera and Image Pro Plus software. Statistical analysis for data collected over time = RM ANOVA Additional eggs were analyzed for fatty acid composition (May samples only - ANOVA)

16 RESULTS

17 Arachidonic acid (20:4n-6) content (%) of fathead egg lipids P<.0001 A 8 B 4 A 8 C 3 10% Soybean oil (SBO) 10% Cod Liver oil (CLO) 5% SBO + 5% CLO 5% SBO + 5% Lecithin

18 DHA (22:6n-3) content (%) of fathead egg lipids P<.0001 A B C C % Soybean oil (SBO) 10% Cod Liver oil (CLO) 5% SBO + 5% CLO 5% SBO + 5% Lecithin

19 EPA (20:5n-3) content (%) of fathead egg lipids P<.0001 C 2 A 6 B 4 C 2 10% Soybean oil (SBO) 10% Cod Liver oil (CLO) 5% SBO + 5% CLO 5% SBO + 5% Lecithin

20 Mean Diameter of Fathead Eggs Over Time Egg Diameter (mm) April May I May II Jun I Jun II July Egg diameter declined over time (P=0.0016) No diet effect or interaction (P>0.05) 10% SBO 10% CLO SBO+CLO SBO+LEC

21 Mean Number of Fathead Eggs Over Time Egg Number % SBO 10% CLO SBO+CLO SBO+LEC April May I May II Jun I Jun II July Egg # declined over time (P=.0001) No diet effect or interaction (P>0.05)

22 Mean Total # of Eggs (+ SE) Over the Spawning Season (April-July) % Soybean oil (SBO) 10% Cod Liver oil (CLO) 5% SBO + 5% CLO 5% SBO + 5% Lecithin

23 Mean Fry Length Over Time 5.5 Length (mm) % SBO 10% CLO SBO+CLO SBO+LEC April May I May II Jun I Jun II July Fry length did not change over time (P=0.1037) No diet effect or interaction (P>0.05)

24 10 additional 1-2-dayold-fry from each pool were stocked into separate petri dishes (initial ph=7.0) ph was suddenly increased to 9 by the addition of a buffered concentrate (control had neutral water added) Fry survival was monitored for 1 hr - counts every 15 min ph Stress Test with Fry

25 Mortality of Fathead Fry Exposed to ph 9 Mortality (%) % SBO 10% CLO SBO+CLO SBO+LEC 0 min 15 min 30 min 45 min 60 min Mortality increased over time (P<0.0001) No diet effect (P=0.15) or interaction (P=0.35)

26 SUMMARY Egg fatty acid content was significantly affected by dietary lipid source(s) of the broodstock Broodstock dietary lipid did not have differential effect on egg # or diameter, or fry length Egg number and diameter decreased significantly over time regardless of diet - fry length was stable Diet effect on survival of fry in high-ph stress test was not consistent

27 Future Research - Baitfish Broodstock Nutrition Maybe we need carotenoids! Don t forget vitamins! What about protein?

28 OTHER OBJECTIVES - CURRENT PROJECT LIPID STUDY WITH GOLDEN SHINERS (THIS YEAR) - SAME DIETS AS FATHEAD STUDY STUDIES WITH DIFFERENT PROTEIN SOURCES WITH FATHEADS AND SHINERS (2004 and later)

29 ACKNOWLEDGMENT BAITFISH PRODUCERS ARKAT TYSON RICELAND NUMEROUS STUDENTS & COLLEAGUES