Aspects of the oyster season in Maryland: Involving labor conflicts detrimental to both seafood and cannery industries, with special reference to the latter

For fully three decades there has been an almost steady decline in Maryland's oyster production... are alarmed for its future. Reasons for decline, data supplied,importance of brood oysters and clutch replenishment. Problems of warm weather and bacterial activity as well as tongs grinding the bottom. Conflicts in canning of early season oysters and late season crops like tomatoes. (PDF contains 16 pages)

Triploidy induction in Heterobranchus longifilis (Family: Clariidae) by cold shock

Triploid was induced in African Catfish (Heterobranchus longifilis) by cold shocking activated eggs at 5 degree C for forty minutes starting 3-4 minutes after fertilization. Triploidy was confirmed from mitotic chromosomes prepared from embryo which showed 100% triploidy in the cold shocking treatment and 100% diploidy in the control treatment

Seasonality, labor and integration of aquaculture into southern African smallhold farming systems

Fish production on Malawian smallholdings is generally limited by the quantity and quality of inputs to the pond (Brummett and Noble 1995). The timing of labor availability and other farm activities limit the amount farmers put into their ponds resulting in lower growth rates and yields. There is potential for improving production and yields through modifications of production schedules to accommodate other farming activities. Limited material and labor inputs among farming system enterprises can be better allocated by considering seasonal availability of inputs and adapting the pond and fish farming technology to the farming system. This case from Malawi demonstrates that aquaculture technology that neglects the annual cycle of events and constraints on the farm will not be easily integrated into the farming system. Focusing on technology that maximizes fish production rather than facilitation of adoption and integration has been a feature of the majority of African smallholder agriculture/aquaculture projects. Farming Systems Research (FSR) must identify niches and opportunities for system improvement for it to be worth supporting as a development intervention.

Induction of mitotic and meiotic gynogenesis and production of genetic clones in rohu, Labeo rohita Ham.

Studies were undertaken to produce genetic clones derived from all homozygous mitotic gynogenetic individuals in rohu, Labeo rohita Ham. ln view of this, attempts were made to interfere with the normal functioning of the spindle apparatus during the first mitotic cell division of developing eggs using heat shocks, there by leading to the induction of mitotic gynogenetic diploids in the F1 generation. Afterwards, viable mitotic gynogenetic alevins were reared and a selected mature female fish was used to obtain ovulated eggs which were fertilized later with UV-irradiated milt. Milt was diluted with Cortland’s solution and the sperm concentration was maintained at 10⁸/ml. The UV-irradiation was carried out for 2 minutes at the intensity of 200 to 250 µW/cm² at 28± 1°C. The optimal heat shock of 40°C for 2 minutes applied at 25 to 30 minutes a.f. was used to induce mitotic gynogenesis in first (F1) generation and at 3 to 5 minutes a.f. to induce meiotic gynogenesis in the second (F2) generation. The results obtained are presented and the light they shed on the timing of the mitotic and meiotic cell division in this species is discussed.

Evaluation on propagation of common carp (Cyprinus carpio Lin.) with hormonal and natural stimuli

The success of breeding of common carp (Cyprinus carpio) using hormonal inducement and environmental stimuli was evaluated considering different sex ratios, and natural and artificial substrates. A total of 18 females (weighing 250 to 2200g) divided into 6 treatments were investigated. A successful spawning was observed in all the treatment groups, only. 66.66% female responded successfully to LHRH-A combined with dompheridone and 83.33% female in natural stimuli. Females induced with LHRH-A and dompheridone found prompt ovulation than that of natural stimulation. A significant variation (F=7.45, P<0.05) was found among the different treatment groups. The number of eggs released appear to depend on body weight (t=15.72, P<0.05), sex ratio (t=7.96, P<0.05) and percentage of ovulated females (t=5.34, P<0.05). Although environmentally stimulated females released more eggs than injected female (t=5.18, P<0.05) but their survival rate was similar (t=1.77, P<0.05). Comparison between the two approaches under the conditions of AIT hatchery shown that both are suitable for spawning induction in common carp. However, environmental stimulation is advantageous because of the less labor and lower cost required for ovulation.

Comparison of effectiveness of heat and cold shocks applied in the induction of gynogenesis in Clarias gariepinus (Burchell)

An experiment was conducted to optimize the procedure of gynogenesis in African catfish, Clarias gariepinus by suppressing meiotic and mitotic cell divisions in fertilized eggs. Gynogensis was conducted by fertilizing normal eggs with UV-irradiated sperm followed by either heat or cold shocking Irradiation of spermatozoa was given for a duration of 1 min and the eggs were fertilized in vitro. Cold shock at a temperature of 3± 1°C for a duration of 30 and 60 min and heat shock at a temperature of 39± 1°C for a duration of 1 and 2 min was applied to induce diploidy. Higher percentage of hatching (68.66) was observed for meiotic gynogens at a shock temperature of 39± 1°C for a duration of 1 min, 5 min after fertilization (af). Higher percentage of mitotic gynogenetic induction (15.33) was observed at a temperature shock of 39± 1°C for a duration of 1 min, 30 min af.