Studies On The Nutritional Physiology And Development Of Artificial Micro-Diets For Larvae And Juveniles Of Large Yellow Croaker (Pseudosciaena Crocea)

A review - advances of studies on nutritional physiology and development of artificial micro-diets for the larvae and juveniles of large yellow croaker (Pseudosciaena crocea, Richardson) was undertaken. A series of feeding experiments were conducted to investigate the nutritional physiology and development of artificial micro-diets for larvae and juveniles of large yellow croaker.Under commercial hatchery conditions, the feeding habits and growth performance of large yellow croaker (Pseudosciaena crocea, Richardson) larvae and juveniles during the first 40 days after hatching (DAH) were studied. The prolarval stage lasted 5 DAH, and postlarval stage appeared from 6 to 20 DAH, when water temperature, dissolved oxygen, pH and salinity were maintained at 24 ± 1℃, 10.1 ± 0.5 mg/1, 8.0 ± 0.2 and 29 ± 3%, respectively. From day 21, it became juvenile fish. The mouth width was 240 um when larval mouth opened at 3 DAH, and then increased to 2480 urn at 40 DAH. The relationship between mouth width and fish age in days was expressed as: y = 0.2327e00682x (R2 = 0.9492). During the first 40 DAH, the larvae and juveniles were fed with rotifers, Anemia nauplii and live/frozen copepods according to a designed regime in commercial practice. The general nutrient composition and fatty acid profiles of these diets differed significantly, and to some degree determined the growth offish. Fish at all stages demonstrated a very obvious feeding rhythm, having a highest feeding peak around 18:00. Besides this peak, the postlarvae and juveniles had another feeding peak around 10:00. They seldom fed during the night, indicating that light intensity determined their feeding activity. The feeding rate and stomach fullness coefficient of this fish at the three stages weregenerally high. The growth rate offish was higher during 1-2 and 21-30 DAH, but slower during 5-9 and 31-40 DAH. The relationships of total length, body length, and body weight to age in days were y = 3.2552e00472x (R2 = 0.9710), y = 3.3205e o.o374x (R2 = 0.9777) and y = 0.0452e 01235x (R2 = 0.9690), respectively. The relationships of body weight to total length and body length were expressed as y = 0.1177x2 - 0.2213x - 0.2651 (R2 = 0.9911) and y = 0.3558x2 - 2.175x + 3.8131 (R2 = 0.9900), respectively. The relationships of mouth width to total length and body length were expressed as y = - 0.0053x2+ 0.2672x - 0.7854 (R2 = 0.9897) and y - -0.008x2+ 0.3747x - 1.1535 (R2 = 0.9909), respectively.Resorption of the yolk sac and development of the digestive tract of large yellow croaker (Pseudosciaena crocea, Richardson) during early life stages (1-40 DAH) were studied using light microscopy procedure. The major events in digestive system differentiation occurred during the early stages. At 3 DAH, the larvae started exogenous feeding as the mouth and anus had opened and communicated with the exterior. The yolk sac was almost completely depleted at 5 DAH. From this time on, the anterior-median was separated from rectum by intestine-rectal valve. At 7 DAH small supranuclear vacuoles appeared in the rectal epithelium, suggesting pinocytotic digestion. By 21 DAH, forked tubers became developed at the epithelial surface of medial and posterior esophagus. At this time, with gastric glands first observation, a Y-shaped stomach was clearly distinguishable and was subdivided into three regions: cardia, fundus and pylorus. Pyloric caeca were first observed at 17 DAH, the number of which increased to 14 until 35 DAH. The liver and pancreas were first observed at 2 DAH. The former became two lobes and elongated to posterior intestine from 4 DAH on. The pancreatic tissue was diffused and distributed around gallbladder, bileduct and portal vein and invaded into the liver, forming a diffused pancreas. Six different diets: three self-prepared micro-diets (MD: D1, D2 and D3), one diet(D4, combined DS with frozen copepods), commercial diets (D5, manufactured by Riqing Co., Ltd and Shangdong Marine Fisheries Research Institute) and frozen copepods (D6) were tested for su...