A study on composition of starter feeds and effectiveness of their use for growing fry of chum salmon Oncorhynchus keta

Low molecular weight peptides in the fish feed can enhance growth of fish fry. The protein-containing components of such feeds as raw and hydrolyzed fish, fly larvae, haprin, hydrolyzed yeast, and experimental extruded starter feeds are examined. The extruded feeds (KRLS-1, KRLS-2, KRLS-3, and EF) were produced by another branch of VNIRO (VNIPRH) on the Amandus Kahl pilot production line (Germany). The contents of moisture, mineral fraction, water-soluble proteins and lipids were assessed using standard analytical procedures and the nitrogen content was measured by Kjeldahl method. Protein fractionation was performed using high-performance chromatography. On these data, daily rations of fry were calculated. Mortality of fry was determined by direct counting. Absolute weight gain was calculated as the difference between final and initial weights of fry. The feed coefficient was calculated as the total amount of feed consumed during the 60-day rearing divided by the weight gain, corrected for mortality. Fish farming tests were conducted according to the standard protocol. The examined starter feeds contained 3.5–6.0 % moisture, approximately 50 % protein, 10–11 % lipids, up to 9 % minerals, and 20–30 % carbohydrates. The hydrolysate from raw fish had the highest portion of low molecular weight peptides (1–10 kDa) – 98 % of the water-soluble protein fraction. Hydrolyzed yeast, fly larvae, and haprin contained 96, 51, and approximately 30 % of low molecular weight peptides, respectively. The extruded feeds were well-balanced and contained substantial amounts of low molecular weight peptides, with the highest content for KRLS-3 (55 %) due to its heightened hydrolysate fraction, whereas KRLS-1, KRLS-2, and EF contained 49, 18, and 35 % low molecular weight peptides, respectively (relative to the water-soluble protein fraction). The fish farming tests demonstrated that the fry fed with KRLS-3 starter feed had the biggest final weight (0.830 g) and the highest mean daily weight gain (1.45 %), with the lowest feed conversion ratio (0.88). The feeds KRLS-1 and KRLS-2 showed comparable results. The feed EF was less effective by growth parameters but provided the best survival of fry (98.9 %, compared to 97.0 % for KRLS-3). All tested starter feeds are quite suitable for industrial rearing of chum salmon fry.