Embryonic Development and Nutritional Requirements of Kutum Fry, Rutilus Frisii Kutum
Haghighi, Davoud Talebi (2006) Embryonic Development and Nutritional Requirements of Kutum Fry, Rutilus Frisii Kutum. PhD thesis, Universiti Putra Malaysia.
This study consisted of a series of experiments that were conducted to determine some biological characteristics, artificial reproduction, embryonic development, optimal level of protein and lipid in artificial diets and food regime spectrum in the stage of secondary nursing of kutum fish larvae (Rutilus frisii kutum). The above study was carried out with artificial reproduction to determine some biological characteristics such as: age, weight, length, percentages of ovary weight to broodstock weight, and also estimation of absolute and relative fecundity and evaluated their relationships in kutum fish broodstock. The results of this study showed that the optimal ratio of female to male was 1:2 (♀ :♂), the first sexual maturity occurred at 2 year old with well developed sexual products with length ranging from 25 cm to 48cm and weight ranging from 213.5 g to 1588 g. Most age, length and weight–frequencies belonged to age groups III+ (23.20%) to IV+ (20%). The results of this study indicated that the absolute fecundity increased as the fish grows, ranging from 12022 to 78856 eggs per fish; on the contrary, relative fecundity of fish decreased with the increasing of fish age and it ranged from 67 to 42 egg for per g of ovary for age groups II+ to VII+ respectively. Correlation coefficient for absolute fecundity against length, weight and age were observed to be r=0.76, r=0.68 and r=0.73 respectively, but the correlation coefficient between relative fecundity against length, weight and age were lower with values of r=0.0.37, r=0.30 and r=0.33 respectively. The stripping of eggs was performed in semi-dry condition. Males and females were injected with carp pituitary gland extracts (GnRh) to induce ovulation at 2 mg of GnRh per kilogram of broodstock body weight. Seven period of embryogenesis were defined; I) the newly fertilized egg was zygote, occurred with 1 cell, with an average egg diameter of 2.21 mm, and mean weight of 9.99 mg and lasted for 15 min. II) Cleavage stage began from 2 to 64 divided cells, with egg diameter of 2.715 mm, weight at 12.99 mg, in 7 hours. III) Blastula stage was made up of early epiboly at the animal pole, with egg diameter 2.8 mm, with weight of 13.51 mg, and time of 26 hours. IV) Gastrula stage was formed when two layers of cells including epiblast which gave rise to ectoderm tissues and hypoblast which gave rise to both mesoderm and endoderm; consequently, the embryonic axis and epiboly were formed at the 90% of gastrulation period. It lasted for 33 h, with egg diameter of 2.96 mm and egg weight of 13.61 mg. V) Segmentation stage began with the formation of the primary organs; somites, early organogenesis, neuromeres, elongation of tail and earliest movement appeared. It lasted for 29 h, with diameter of egg at 3.04 mm, weight egg of 13.24 mg. VI) Organogenesis occurred with rapid development towards functionality in most organs, particularly the senses, the heart and the gut. It lasted for 15 h with egg diameter of 3.16 mm and weight of 14.64 mg. VII) Hatching ended when the larvae were pelagic and avoids sinking. It lasted 20 h after organogenesis with diameter egg 3.009 mm and weight 14.39 mg. Total times for hatching was 130 hours and 15 minutes. Food regime spectrum of kutum fry at the secondary nursing under pond culture condition was estimated based on their stomach contents analysis. During the rearing period water temperature varied from 16°C to 28°C. In general, the frequency and diversity of phytoplankton included 5 phylums, 10 orders, 21 families and 36 genuses and zooplankton community included 5 phylums, 10 orders, 12 families and 31 genuses were obtained from gut contents analysis of kutum fry. Observation was carried out Observation was carried out periodically for 11 weeks, and it was found that kutum fry collected its food from below to surface of water. The results of this study indicated that kutum fry had low growth and high mortality at the early stage of rearing period. When the intestinal digestion system became more developed, the utilization of greater diversity of food items increased. The feeding regime spectrum of kutum fry consisted of phytoplankton, zooplankton, benthos, detritus and artificial food. Determination of optimal level of crude protein in kutum fry diet was conducted with five levels of protein concentrations (35%, 40%, 45%, 50% and 55%). The results showed significant difference among 5 concentrations on growth of fish (p<0.05). The best final weight was 1095 mg, weight gain of 877.3%, specific growth rate of 3.21%, protein efficiency ratio of 1.00, food conversion ratio of 1.99, and at 28% mortality obtained at 50% protein level diet. Polynomial regression analysis between protein levels and weight gain of fish indicated that a weight gain peak was obtained at 46.8% protein level. Results of this experiment showed that the optimum protein level of kutum larvae for best growth was 46.8%. Determination of optimal level of crude lipid in kutum fish fry diet was conducted with four levels of lipid concentrations (8%, 10%, 12% and 14%). The results showed significant difference among lipid levels on growth of fish (P< 0.05). The highest final weight was 1926 mg, weight gain 852%, specific growth rate 2.78%, protein efficiency ratio 1.07, food conversion ratio 2.05 and mortality 2.5% obtained when dietary lipid level was 8%. Polynomial regression analysis between lipid levels and weight gain of fish indicated that a weight gain peak was at 7.67% lipid level. Result of this experiment showed that the optimum level lipid of kutum larvae for best growth was at 7.67% lipid level.
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