A comparison of dry, live and combination diet on the efficacy of raising zebrafish fry

1. Fry aged 4 days Fry at 10 days Fry at 15 days Fry at 28 days Live Live Live Live Dry Dry Dry Dry Combined Combined Combined Combined 4mm 8mm 13mm 24mm Bar graph of fry survival rate at 28 days Bar graph of average length of fry at 28 days Bar graph of average weight of fry at 28 days <100 micron dry food fed to fry that were 4-9 days old Paramecium that was fed to the fry that were 4-9 days old Instar 1 Artemia that was fed to fry that were 10-28 days old 100-150 micron dry food fed to fry that were 10-28 days old Diet for the fry: A comparison of dry, live and combination diet on the efficacy of raising zebrafish fry David Maley, Neil Campbell & Carole Wilson UCL Fish Facility, Department of Anatomy & Developmental Biology, Gower Street, London, WC1E 6BT Aim: This pilot experiment was conducted on three commonly used diet types in zebrafish facilities to raise fry. The aim of this experiment was to get the best survival and growth rates while using a 3 times-a-day feeding regime currently used in the UCL facility. The 3 types of diets that are used for feeding zebrafish fry were an exclusively dry diet, an exclusively live diet and a combination of dry and live diet. Method: Nine 3 litre tanks were set-up, 3 fed dry food, 3 fed live food and 3 fed the combined diet. Each tank had 50 wild-type fry in, so 150 fry for each type of diet. The fry were fed 3 times a day, at 09.30, 13.00 and 15.30. The fry were all fed exactly the same quantities in increasing amounts as they got older, irrespective of diet, for the time they spent in the nursery. The fry went into the nursery at 4 days post fertilisation and were removed from the nursery at 28 days post fertilisation. On the 28th day the fry were removed individually from each tank, anaesthetised and then measured for weight and length, and also counting the survival rates for each tank, then the results were calculated. Results: Introduction: In the wild, zebrafish are found indigenously to Southern Asia. These zebrafish populations can be found in streams, canals and ponds feeding on small crustaceans, insect larvae and some vegetation. In research, zebrafish have been historically used to study developmental biology, but as a model other fields of research have also begun to use the zebrafish and these include immunology, toxicology and disease modeling. The transparency of the embryo, ex-vivo development, fast development times and fecundity makes them an ideal model to use in research. With the increased use of zebrafish as a research model there has become an need to standardize their husbandry to increase their breeding performance, embryo viability and the health of the fish. Along with environmental conditions, a source of nutritionally appropriate food is essential for zebrafish, especially their developing fry. The results from the experiment we conducted showed there was a significant difference in survival rate between the combined diet and both of the other diets investigated {(p≤0.05) one way ANOVA}. There was no significant difference between the survival rates of the live and dry diets. On average the length and weight of the fry fed the combined diet appeared to be greater than that of the dry and live diets, but this was only slight and not significant. Discussion: The combined diet clearly displayed an increased level of survival, when compared with the other 2 diets. The percentage achieved is comparable with survival rates from similar feeding regimes incorporated in our facility, which produce survival rates in the region of 80% (personal observation). The dry and live diets yielded similarly low survival rates, suggesting that both are nutritionally insufficient in isolation. The results from the length and weight, however, are less clear cut. While the average length and weight in the fry fed combined was slightly higher, the averages of the dry and live were skewed heavily upwards by several much larger individuals in each case. The small survival rates of the dry and live diets meant the remaining fish (in one case only 5) were able to eat much more food than was planned. Carvalho et al. (ii) showed that good survival, growth and length could be achieved by providing a constant source of even nutritionally poor diet and this is likely to be the case in this trial. The recirculating system was set to a very low flow and excess food would remain in abundance, especially in the later stages of the trial. It could then be argued that continuous pulse feeding as used in aquaculture, would be beneficial for successful larval rearing. However, the logistics of such a system are prohibitive, not least due to the size of diet and the possibility for decreasing water quality. To clarify the effect on length and weight in future trials, it will be necessary to alter the experimental design, specifically by changing the amount of diet fed to percentage biomass per day method. This is commonly used in nutritional trials and accounts for changes in fish numbers and size. In keeping with the 3R’s, it may be seen as ethical to achieve as higher survival rate as possible, and it is likely that healthy, well developed fry will become healthy adult fish showing higher level fertility and fecundity. Conclusion: The conclusion to the pilot experiment was that the combined diet produced the highest survival rate, average fry length and average fry weight. Reference: (i) C. Lawrence - The husbandry of zebrafish (Danio rerio): A review - (Aquaculture, Volume 269, Issues 1-4, 14 September 2007, Pages 1-20) (ii) A.P Carvalho, L. Araujo and M.M. Santos - Rearing zebrafish (Danio rerio) larvae without live food: evaluation of a commercial, a practical, and a purified starter diet on larval performance - Aquaculture Research 37 (2006), pp. 1107–1111. Acknowledgements: The UCL fish facility is funded by The Wellcome Trust, BBRSC, MRC & UCL