The effect of extenders was studied on the cryopreservation of sperm from African catfish, Clarias gariepinus (Burchell). The following six basic extenders were tested: fructose, glucose, sucrose, NaCl, KCl solutions and the artificial seminal plasma of the African catfish. Each of these extenders was tested both with and without buffer systems (i.e. NaHCO3‐CO2 and Tris‐HCl) by using 10% dimethyl‐sulphoxide (DMSO) as a cryoprotectant. The two‐step freezing was carried out in a programmable freezer by using the following freezing rates: (1) 4 °C min–1 between 3 and –4 °C; (2) and 11 °C min–1 between –4 and –80 °C. The best post‐thaw motility (25%) was achieved with 333 mmol L–1 fructose solution and NaHCO3 buffer. The fertilization experiments were carried out with unbuffered fructose and glucose extenders using various amounts of sperm and two fertilization methods: (1) dry and (2) wet. The best fertilization rates were achieved with 75 μL of sperm and wet fertilization with glucose extender, or 100 μL of sperm and dry fertilization in case of fructose – both methods fertilized 96% of all eggs.
Feeding dried and vitamin C enriched decapsulated Artemia cysts to African catfish larvae increased their growth rate significantly after 6 days over those fed only freshly decapulated cysts. Groups fed with Artemia nauplii had a significantly higher growth during the experiment, although this difference was not considerably important in practice. Tank colour had no influence on growth. Because of their lower price, the decapsulation of lower quality cysts can be an appropriate feed source in intensive cultures of African catfish larvae. 1999 The Fisheries Society of the British Isles
Four distinct forms of native gonadotropin-releasing hormone (GnRH) and two newly designed analogues were tested for their in vivo activity to induce ovulation in African cat¢sh. The e¡ects of these peptides on ovulatory parameters were compared with those of carp pituitary and [D-Ala 6 , Pro 9 -NEt]-mammalian GnRH analogue (mGnRHa), two tested ovulation-inducing agents in African cat¢sh. Assessment of ovulation was carried out by determining the ovulation ratio and the relative quantity of egg produced. From the results of the experiments, the order of potency of the native GnRH peptides is summarized as chicken GnRH-II (cGnRH-II) 4salmon GnRH (sGnRH) 4mammalian GnRH 4chicken GnRH-I (cGnRH-I) .Chicken GnRH-II was as potent as mGnRHa while cGnRH-I was totally ine¡ective. The new D-Orn 6 -cGnRH-II and D-Orn 6 -sGnRH with a substitution at position 6 with D-isomer residue were as potent as the most extensively used mGnRHa, indicating that the position 6 modi¢cation might be more crucial than the substitution at the C-terminal. On the basis of our results, the potential use and incorporation of cGnRH-II and sGnRH for the development of more generic spawning induction therapies are suggested.
European catfish, Silurus glanis, is an important species for aquaculture in temperate climates. At present, its production relies mainly on pond culture. However, European catfish could be a promising candidate for intensive aquaculture since it has a high growth rate on commercial diet, is resistant to handling and has relatively low requirement for water quality. In this study we compared the results from induced breeding of European catfish broodstock reared in an intensive system or in a pond environment.Induced breeding experiments were conducted in two consecutive spawning seasons using European catfish broodstocks with different origins. One broodstock was cultured in an intensive system, while the other was reared in artificial pond conditions. One day before the experiments, fish were transferred to the hatchery and placed in 4.0 m 3 polypropylene tanks with running water. One experimental group contained fish cultured in an intensive system, while the other consisted of fish reared in pond conditions. Fish in both groups received an injection of dry carp pituitary administered in 0.7% NaCl at a dose of 4.0 mg kg -1 body weight. Assessment of ovulation was carried out by determining the ovulation ratio (number of ovulated females / number injected) and by the pseudo-gonadosomatic index (PGSI) calculated as follows: (weight of stripped egg mass / body weight of the female before stripping) 100. When ovulation was detected, the eggs were stripped and weighed. Fertilization rate of the eggs was used as a parameter for egg quality.In both spawning seasons, five out of six females reared in pond conditions ovulated after the treatment, while pituitary injection induced ovulation in all females cultured in an intensive system. Mean fertilization rates for the two groups were high and statistically similar in both seasons (P>0.05). The mean PGSI values, however, were significantly higher (P<0.05) for the females cultured in the intensive system in both seasons. In conclusion, this study shows that European catfish females reared in intensive conditions from larval stage to maturity at constant temperature of 21.0±1.0°C can be induced to ovulate by pituitary injection. The reason for the high relative fecundity of these females was probably the constant temperature that secured continuous ovarian development all year round. Results from the propagation of fish reared in pond conditions were similar to those from hatchery breeding of European catfish that has been carried out routinely for years.
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