Reproductive biology of Catla catla in the Udawalawe reservoir, Sri Lanka

The reproductive biology of Catla catla (Hamilton-Buchanan) in the Udawalawe reservoir was studied from June 2007 to December 2008. Samples of eggs from Indian major carp C. catla were collected from fish landed in the reservoir and analysed in the laboratory to assess the reproductive characteristics. C. catla. Cirrhinus mrigala, exotic Cichlids and Labeo rohita accounted for 62.2%, 21.0%, 12% and 1.0% respectively of the total landings in the Udawalawe reservoir during the study period. Gonads of C. catla were collected in the field and examined in the laboratory to determine the stage of maturity and fecundity. Data on fish length and gonad weight were collected to estimate the gonado-somatic indices (OSI). Landed catches were also examined in the field to determine the sex ratio of C. catla in the catch and was found to be 1:5.6 male to female. Results of fecundity estimates revealed that C. catla females in the Udawalwe reservoir were fully mature in June and October of the year. From the monthly variation of OSI, two recruitment pulses per year were evident. The length of the body at first maturity in female C. catla in the Udawalwe reservoir was estimated to be 74.2 cm.

Physiological and biochemical study of over-ripened oocyte in the cultivated Caspian brown trout (Salmo trutta caspius) and determination of egg quality markers

To determine the best time for egg stripping after ovulation and over-ripened oocyte in the Caspian brown trout (Salmo trutta caspius), the eggs were retained in the parental abdominal cavity for 40 days post-ovulation (DPO) at 7±0.6°C. Eggs were stripped every 10-day interval in 4 treatment and were fertilized with a pool of semen obtained from 8 males. Also, the physiology and biochemistry of the eggs and ovarian fluids were studied. Results showed that the level of eyed eggs and hatched alevins declined with over-ripening time: that is, the expected amounts (90.65 ± 6.28% for eyeing and 86.33 ± 6.82% for hatching) in newly ovulated eggs (0–10 DPO) decreased to 0.67 ± 1.34% and 0.49 ± 0.98%, respectively, in over-ripened eggs (30–40 DPO). However, larval abnormalities remained constant for 30-days after ovulation. During the course of oocyte over-ripening, the pH of the ovarian fluid significantly decreased and the concentration of glucose, protein, calcium, iron, and aspartate aminotransferase activity significantly increased. Moreover, the concentration of protein, triglycerides, and aspartate aminotransferase activity in the eggs also changed. In the newly ovulated egg, the yolk consisted of homogenous tissue and its perivitelline space diameter had no considerable differences. With over-ripening, the yolk became heterogeneous, while chorion diameter and micropyle did not change. The perivitelline space diameter varied among different areas. The present study demonstrated that the best time to take Caspian brown trout eggs after ovulation at 7± 0.6°C was up to 10 DPO. Among the studied parameters of the egg and ovarian fluid, egg quality was related to both ovarian fluid parameters (e.g., pH, protein, aspartate aminotransferase, glucose, cholesterol, triglycerides, calcium, iron) and egg parameters (e.g., cholesterol, triglycerides, iron, aspartate aminotransferase). Thus, these parameters can be used as a egg quality markers in this species.

Examining the possibilty of multiplication and breeding of (Schizothorav [sic] zarudnyi) in order to restoration of regional aquatics reservations of Hamoon Lake and taking its advantag [sic] for aquaculture

Schizothorax zarudnvi, is an endemic fish of east country waters. (Triple lagoons of Hamoon and relevant water resources) that in the world it is reported in this resource specially. This fish named Hamoon mahi is one of the most economically valuable species in this region. Because of the recent years droughts, Hamoon logoon has been drive since 2000. Also, semi-wells (a semi natural resource) were affected drastically by recent drought years and their volume reduced to nearly one third of their real volume and resulted in changing at growth and reproduction physiology process in Schizothorax zanidnyi, brood stocks. Beginning of this project was done from October 2003. It's field studies begun (brood catching) since November 2001 by two methods including entangling gairs and at semi wells of Sistan that (Beach seine) had maximum rate of preparing qualified brood stocks. Broods transferred to Cyprinidea reproduction work shop of Zahak and after taking primary measures they stored in to the edaphic pools. Increasing the success safety factor (coefficient) for artificial reproduction of Sthizothorax zarudnyi , identifying the appropriate tune for Hormonal acceptance (physiological preparation of broods) is needed , so this important work was done regularly by histological studies and GSI measurements since November. Highest GSI rates of females (%80.51) and highest IV stage abundance of sexual maturity (%l 00) were observed an march. On the base of this date, Hormone therapy was done on broods on march. The used hormones are as follows Hypophysis. extraction, GnRHa and Anti Dopamin at the dozes of 3-6 ml, 20-30kg and 10-15 ml per kg body weight respectively and 2-3 times from 11-12-80 they were injected. Injected broods kept in to two circumstances, flow-through (rounded pool) and stagnant systems. In stagnant system 14 and 19 individuals of female and male (Schizothorax zauiulnri) broods, respectively injected in 11th, 15111, 19th, and 24th of march 1380. Non of the injected broods in 11 and 15 and 19th march (in stagnant Condition) answered to Hormone therapy. After final injection broods had general less activity and a few of them died. Mean temperature of brood pond waters (daily) which were injected. Fluctuated between 10-25-13. 63°c but injected broods on 24th march had different characteristics. They had pale color and had few fecundity. In this stage of injection they hadn't any successful vulation. After injection, Mean daily water temperature was 15, 88-17, 54°c. In Flowing system, 13-16 individual of males and females respectively were injected on 15th, 19th, 22th and 23th march. None of injected producers on 15th and 19th march with mean daily water temperature of 10, 25-12°c were prepared for spawning but injected producers on 22nd an 23th march with mean daily water temperature of 13.5-1 rc responded about 75-100 percent. (Schizothorax zarudnyi) brood stocks were prepared for spawning after 353-428 hours/day from final injection. Diameter of obtained eggs (before fertilization) was between 1.9-2.3 min and of fertilized eggs was 3.8mm. Fertilized eggs of (Schizothorax zarudnyi) were hatched after 6-7 days with mean water temperature of 17.08°c. Mean length of on one day larvae was 9.47 mm. Larvae was 9.47 mm. Larvae adsorbed the whole yolk sac after , 5-6 days at 17- 1°c and were prepared for releasing in to edaphic pools. Because of the lack of necessary and complementary facilities in the region , they had to release them in to veniros and growing them for 8 days. At the end of 18th day , 35000 larvae (at first) released into an edaphic pond with a volume of 150m2. After growing them for one moth , mean length and weight of new hatched larvae was 29.41 mm and 1.12►r , respectively. With respect to results of this investigation , artificial reproduction of (Schizothorax zarudnyi) Can be possible at 14-17°C and flowing water with Hormonal treatment. It -s breeding has increased development than other cultural specious in the region. Due to high economical value of this specious in Sistan and ti-s specialization east waters of Iran and having high resistance and proper growth There is a need of it's development and reproduction and culture in fish culture fanns (edaphic ponds• two-purpose pools) at the region and country.

Notes on the larval rearing scheme at SEAFDEC/AQD

For tiger shrimp, milkfish, and sea bass, larval rearing starts with the hatching of artificially spawned eggs. The eggs are stocked in larval rearing tanks, hatched, and metamorphosed larvae are fed and reared with good water management. Fry are harvested after about 30 days.

Study biological characteristics related with development and reproduction in Barbus capito on the southern coast of the Caspian Sea, Gilan Province

In the present research, a total of 207 pieces of fish from 25 sampling stations in Gilan Province coasts in the years 2001-2002 were biologically studied in terms of their growth and development, reproduction and feeding. The average length and weight of the fishes are increased, as they get older. The highest index of length and weight growth is observed in the years 1 to 2. As the age increases, gradient of length and weight growth diagrams decrease. In studying the relation between length and weight, it was observed that proportionate to the total length, the weight is increased progressively. The fatness coefficient index in the initial years of life and prior to maturity is higher than the post maturity period. As the age increases, the decrease of this index is observable. The fatness coefficient index rate is directly related to index of fullness. The highest Gonadosomatic Index is seen in the months of June and July, i.e. at the times of spawning; and the lowest index rate is observed in the months of November and December. The appropriate temperature for reproduction of these species is from 18 to 22 degree centigrade. The Gonadosomatic Index is higher in spring and summer seasons as compared with autumn and winter. Besides, as the fishes become aged, the amount of the said index increases in a manner that the gradient of it in the years to maturity is less than the maturity time and thereafter. Sexual maturity stages in different months are directly related to Gonadosomatic index, and increase as the age increases. The sexual ratio of male fishes to the female fishes in terms of number is plus one prior to maturity; about one at the time of maturity and minus after maturity. In general the frequency of male fishes as compared with female fishes in all group ages is approximately two times. The fecundity mean, and the diameter and the rate of eggs will substantially increase, as the Gonadosomatic index rises. The maturity age in the male fishes is 3 to 4 years and in female fishes is 4 to 5 years. The spawning of this species in rivers occurs repeatedly and in different time intervals, and do not take place once (Asyncronous). The Gastrosomatic index is directly related to index of fullness and will decrease, as the age increases. The index of fullness is relatively the months of April and May. The underlying reason is the need of the fishes to energy for reproduction. As the spawning time commences, the index of fullness moves down and the downward direction continues. After spa g mg and reduction of the volume of energy in the body, the index of fullness rises, and it will be substantially high until the beginning of fall. In fall and winter as it gets cold, the index of fullness moves downward and the body fat deposits are used. A correlation is shown between the changes in vacuity index and fullness indices. This means that as the fullness index rises, the vacuity index decreases, and vice versa. The Hepatosomatic index prior to the reproduction is at the highest amount and after spawning is at the lowest. No correlation is observed between the fullness and Hepatosomatic indices. In other words reproduction is an inherent and instinct originated matter; and its cycle goes on, alternately and in an orderly manner, upon completion of germinal cells, even when it coincides with reduction or stoppage of somatic cell growth. The rising trend of Hepatosomatic starts in August and will continue until the next July. The volume of fat around digestive tract is severely reduced in early spring and this trend will reach its apex in summer season. In the cold seasons, i.e. the fall and winter, the accumulation of fat around digestive tract increases. Consequently, a meaningful and inverse relation is observed between index of fullness, also the progress of sexual maturity stages and the volume of fat.

Biology and distribution of grouper (Epinephelus coioides) in province waters (Abadan Bhrakan)

This survay has been done from Januray 2000 till May 2002 in Khouzestan costal waters. Four species of grouper were identified from which orange spotted grouper (Epinephelus coioides) was the dominant species. For studing environmental parameters and reproductive biology, age, growth parameters and mortality rate samples were collected by fishing ship. Samples were taken montly in 4 days by fishing traps and trawls. In addition, some samples were obtained from Khozestan fish landing centres. Environmental factors such as PH, 02, salinity, water temperature and depth of traping areas, were measured. To identify species, morphometric characteries of 452 individal fishes were measured. Stomach contents of 394 fish were has survaid, from which stomach of 226 fish, and 168 fish had empty stomachs. Percentage of empty stomachs (cv) in males was more than females. Food items found in 73 percent of stomach were crab (11%), shrimps (8.8%) , squids (3.9%), gastropods (17%) and bivalves (0.4%). Feeding intensity in year classes did not obay logic trends The importance relatively indicator (I.R.I) were 81, 9.9, 4, 1.5 and 0.3 percent for fish, crab, shrimp, squid, gastropod and bivalve respectively. For age determination, sagita otoliths of 450 fish were taken and countable sections were obtained from 425 specimens. Relative frequency distribution of opaque and transparent rings showed that each opaque growth ring generates once a year from November to September. It seemed that generation of opaque rings is affected by temperature and photoperiod changes. Correlation between length and age was calculated using Von Bertalanffy's least square method. Following equasion was obtaind: L(t) : 122.27 (1 e 0.146 (t+0.482)) Growth parameters were determined through by Ford Walford equasion and Response Surface and Shepherd subcommands in Elefan program and L00 and K amounts were have determined. Correlation between length and age of 635 fish was determined by gender . Length and age correlation was calculated by exponential model and between total length and standard length by straghit line model. Correlation between age and weight of sagita was calculated by total length and age. The most Correlation was between sagita weight and fish age (r=0.876). Total mortality rate (z) was estimated by Length Converthed Method , Jones and Vanzaling and Powel Wetherall. Total mortality rate was z=0.39. Natural mortality rate, using Pauly method was calculated M=0.32. Fishing mortality (F) was 0.08. Gonads of 425 fishes were surveid within 18 month, from which 363 were female, 46 were male and 16 were sex reversing individuals .Total length of females varied from 26 to 95.5 centimeters while males length varied from 56.5 to 107 centimeters. Sex reversing individuals had a length of 47.5 centimeters, when two years old and 62.5 centimeters at age of 3 years. From the mentioned 425 fish, 401 individuals were matured, containing 339 females and 62 males, 5.47 females against each male. Montly changes of Gonadosomatic Index (GSI) by total body weight and standard length and total body length showed that this index increases from march to May and maximum increase was in May . This experiment was adapted in spawning season. Potential, relative, and absoulate fecundity was estimated by counting eggs in three samples. Total amount of traped fish using special traps was 16182.18 kg from which Epinephelus coioides provided catching 15353.43 kg of it (91.27 %) and By catch was 141.18 kg (8.24 %). Total average CPUE for whole catch was 123.33 kg/day/vessel. Total amount of catch was estimated 232.04 tons, considering CPUE of total catch and total Khuzestan trap ships effort.

Survey of marine turtles ecobiology in north of Persian Gulf

Sea turtles are counted as rare and extincting species. During the last century the population of sea turtles are drastically reducd and the remaining ones are considerd either threatend or endangerd because of some factors as sea pollution, economic benefits, intense fishing effort, beach man-made structures and so on. So, in recent years, more attention to conserving and surviving them is assumed. After a preliminary studies on some of the biological specifications in northern beach of Persian Gulf, three islands ; Hormoz, Hengam and Larak for the biometry of the turtles, a total number of 179, from 1999 to 2002 (4 years) are chosen. Some of the biological attributes as weight, length and their egg-laying are recorded, these items are then analyzed using SPSS software. The observed results are as follows . The lowest weight of the turtles was 35 kg, the highest 59 kg, and the average 45.24 kg. The lowest carapace length was 64 cm. the highest 86 cm and the average 76.79. the lowest number of laying eggs was 73, the highest 126, and the average 86.79. The results are discussed in three following sections: 1-A contrastive analysis of the biometric characteristics during 1999 in the three mentiond islands. 2-A contrastive analysis of the biometric characteristics in Hormoz island from 1999 to 2002. 3-A contrastive analysis of all the biometric characteristics in the three islands and other parts of the world. The results obtained from the turtles biometry in 1999 shows that the average of the turtles weight in Larak is lower than the other mentioned ones, and the heighest average is observed in Hormoz island. The turtles of Hengm have laid more eggs than the others. The results of Hengani turtles biometry during 1999-2002 indicates that the average of their weight in 2002 is more than the other three years in the same place. The least number of eggs laid during these years are 53 and the most are 126. The most number of eggs are laid in Hormoz in 2002, but the average number does not show any significant change.

Survey of biosystematic and sexual reproductive physiology in Holothuroidea on Hormozgan Province

Sea cucumbers belong to phylum Echinodermata, order Holothuroidea are an abundant and diverse group of Invertebrates, with over 1400 species occuring from the intertidal to the deepest oceanic trenches. Sea cucumbers are important components of the food chain in temperate and coral reef ecosystems and they play an important role as deposite feeders and suspension feeders. Rapid decline in populations may have serious consequences for the survival of other species that are part of the same complex food web,as the eggs, larve and juveniles constitute an important food source for the other marine species including crustaceans, fish and mollusks. In addition sea cucumbers are often called the earthworms of the sea, because they are responsible for the extensive shifting and mixing of the substrate, and recycling of detrital matter. Sea cucumbers consume and grind sediment and organic material into finer particles , turning over the top layers of sediment in lagoons , reefs and other habitats and allowing the penetration of oxygen. While the taxonomy of the holothurian families is generally well known , the distinction of similar species is difficult. There are relatively few holothurian taxonomist.Most sea cucumber species can be identified by Holothurin taxonomists by using the calcareous skeletal ossicles found in the body wall. In this study , at first a sea cucumber from Kish island in Persian gulf has recognized. Individuals collected from west and east extend far away into north and south of coral reefs by diving. I have checked them morphologically and anatomically.Then with key to the orders of the Holothuroidea, They belong to the Aspidochirotida with key to the families of Aspidochirotida, they were in Stichopodidae families and with key to the genus of Stchopodidae, they were Stichopus. Then ossicles were extracted at National Museum of Natural History, by Dr David Pawson. The ossicles were measured on a transect across a slide prepared from the mid-dorsal region of each specimen.The one we have in the shallow waters of Kish island, is Stichopus hermanni, a massive holothurian, body broad, considerably flattened ventraly ,the dorsal side slightly arched and the lateral sides almost vertical; body wall fairy thick and soft ; mouth subterminal; anus central; tentacles usually 20 in number of length and leaf shaped. Numerous ossicles consisting of table with large discs having usually 7 to 15 peripheral holes, but often irregular or incomplete and spire of moderate height ending in a group of spinelets, rosettes of variable development, and c-shaped rods. Color (exept papillae)partly remained after preservation in alcohol which is found at the depth of 4 to 8 meters, on coral reef. Furthermore, the sexual reproductive cycle was described using standard methods. Gonads were removed and transferred to Bouin's fixative for four weeks and then processed according to standard embedding technique. To prevent the loss of tubule contents during embedding, the tubule sections, were cut well beyond the segment selected for sectioning. For each individual, six sections, each section with 5µm diameter by microtome were cut from tubules. These sections were first placed on gelatin coated slides (the gelatin was heated to 42°c) and then transferred to the oven at 37°c for one hour. This technique usually prevents the fragil tubules from breaking and the loss of gametes. The slides were stained with Eosin and Hematoxylin, and good resolution of the various cell types achieved.A second series of slides was stained with the Periodic Acid Schiff(PAS) to identify polysaccharides(glycogen). Monthly sampling was occurred.The sexual reproductive cycle was defined through the combined use of these criteria: Monthly percentages of the gonad stages for each sex, the monthly gonad index (GI) , given as the ratio of the wet gonad weight (G) to the dray weight (DW)and the monthly percentage of individuals that undetermined sex. The gonad consists of two tufts of tubules on which saccules develop. Gonadal development was classified into five stages: post spawning, recovery, growth, advanced growth, and mature stage that were adapted from the earlier studies of holothurians. Histological preparations showed that the sex of larger individuals could be identified by the presence of oogonia and young oocytes in females, and spermatogonic stages in males.The mean diameter of the tubules and gonadal mass follow annual cycles, increasing from late winter through spring, and dropping abruptly after spawning in the summer. Gametogenesis is generally a prolongate process and begins in March. By summer the ovarian tubules contain oocytes with diameter of 120-240 pm and the testicular tubules contain an abundance of spermatozoa (diameter 5-6 gm ).Following spawning the predominant activity within the spent tubules is phagocytosis of the residual gamets.The active phase of gametogenesis (March to July), coincides with an increasing photoperiod regim, and an accelerated gametogenesis occurs in July when temperature is high. Throughout the year, the gonad of Stichopus hermanni is larger in males than in females, and this is due to the number of tubules in the testis rather than to tubules length or diameter.

The natural life history of milkfish

Following brief descriptions of the various phases in the natural life history of the milkfish (Chanos chanos), namely adults, eggs and embryos, larvae, fry and metamorphosis, juveniles and sub-adults, a summary is provided of the life history, providing also a schematic diagram.

Epidemiology of bilharzia (Schistosomiasis) among fishing communities of Lake Victoria

The study was done in six districts of Mukono, Jinja, Iganga, Bugiri, Busia and Kalangala. At both mainland shoreline and islands, 271 adult respondents were randomly selected from 17 landing sites of Lake Victoria over a four months period between October 2000 and January 2001. A questionnaire was administered for symptoms of schistosomiasis and samples of stool, urine and blood were taken from respondents. Stool and urine were analysed for schistosome eggs and blood. Blood was analysed for increased eosinophils. Snail samples were collected from various depths along the shoreline of study sites identified and screened for schistosome cercariae.

The diversity of macro invertebrates in the Victoria and Kyoga lake basin and their relationship to ecosystem functioning

Aquatic macro-invertebrates encompass all those organisms that be seen with unaided eyes. Most macro-invertebrates are categorised as semi-aquatic in that they are aquatic in early stages, but live as terrestrial organisms as adults, while others like gastropods, bivalves, Oligochaetae, Hirudinae and ostracods are exclusively aquatic. Some of them such as mayflies lay eggs in water and subsequent stages also live in water until adulthood when they emerge to live a terrestrial life. In others, eggs are laid near the water, while some like members of Tendipedidae (midges) lay their eggs on the leaves of aquatic macrophytes and after hatching their larvae creep into water

Trophic interrelationships and food-webs among the fishes in ecosystems of the Victoria and Kyoga lake basin

The Victoria and Kyoga lake basins had a high fish species diversity with many fish species that were found only in these lakes. Two Tilapiines species Oreochromis esculentus and Oreochromis variabilis were the most important commercial species in these lakes and were found nowhere else on earth except in the Victoria and Kyoga lake basins (Graham 1929, Worthington 1929). Lakes Kyoga and Nabugabo also had endemic haplochromine species (Worthington 1929, Trewavas 1933, Greenwood 1965, 1966). As stocks of introduced species increased, stocks of most of the native species declined rapidly or disappeared altogether. The study was carried out on Lakes Victoria and Kyoga, River Nile, some selected satellite lakes from the two basins namely Lakes Mburo, Kachera, Wamala, Kayanja, Kayugi, Nabugabo, Victoria, Victoria nile and River Sio(Victoria lake basin). Lakes Kyoga (Iyingo), Nawampasa, Nakuwa, Gigati, Nyaguo, Agu, Kawi and Lemwa (Kyoga lake basin). Species composillon and relative abundance of fishes were estimated by detennining the overall average total number of each species encountered. A trophic consists of species using the same food category. Shannon-Weaver Index of diversity H (Pielou, 1969) and number of trophic groups, were used to estimate the Trophic diversity of various fish species in the lakes. Food analysis has been done on some fishes in some of the sampled lakes and is still going on, on remaining fishes and in some lakes. Generally fish ingested detritus, Spirulina, Melosira, filamentous algae, Planktolyngbya, Microcysists, Anabaena, Merismopedia, Spirogyra, higher plant material, rotifers, Ostracodes, Chironomid larvae and pupae, Choaborus larvae, Odonata, Povilla, Insect remains, Caridina, fish eggs and fish. Eight trophic groups were identified from thes food items ingestes. These included detritivores, algae eaters, higher plant eaters, zooplanktivores, insectivores, molluscivores, prawn eaters, paedophages and piscivores. Trophic diversity by number of trophic groups was highest in Lake Kyoga (6) followed by lakes Kayugi, Nabugabo, River Nile and Mburo (3) and the lowest number was recorded in kachera (2).

Observations on the biology of Nothobranchius guentheri (Pfeffer) (Cyprinodontidae), an annual fish from the coastal region of East Africa

Nothobranchius guntheri is found in seasonal pools and streams in the coastal region of Tanzania. A population recurring annually in a pond near Kilosa has been studied. Growth in length was rapid and maximum mean lengths were attained within 11-12 and 7-8 weeks of hatching by males and females respectively. Males grew larger and exhibited wider variation in length than females. N. guentheri shows clear sexual dichromatism. No significant inequality in the sex ratio was found. Females with ripe eggs were found 7-8 weeks after hatching. Spawning continued throughout adult life and fecundity increased markedly with increasing length. In laboratory aquaria, aggressiveness between adult males was noted and females were actively driven on to the substratum preparatory to spawning. The diet of the fish pond consisted chiefly of aquatic and terrestrial insects, of which midge larvae and pupae were the most common. N. guentheri is exploited by man in the aquarist trade and for the biological control of mosquitoes. An extended redescription of the species is appended which includes N. melanospilus (Pfeffer) as a synonym.

Growth rates of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) under cultivation in ponds at Nyegezi, Tanzania

Aquaculture in Tanzania is still on a subsistence level and most of the ponds are maintained as part time job. The ponds are too small, shallow and over crowded with stunted Tilapia spp. In the present paper the results of experiments conducted in ponds at Nyegezi with T. esculenta and T. zillii are presented. This was part of an overall project of developing techniques of fish cultures with Tilapia under the limited existing conditions at Nyegezi. In a mono - species culture experiement with Tilapia zillii in nine month's time an average size of 172.8 mm/115.0 g was attained. In another experiment with T. zillii and T. esculenta in thirteen month's time, T. zillii attained an average size of 180.2mm/106.6 g and T. esculenta 193.6 mm/118.8 g. In another experiment with intensive feeding schedule an average size of 179.3 mm/126.6 g was attained by T. zillii and 191.0 mm/125.0 g by T. esculenta in four month's time. A locally prepared supplimentary feed with local Brewery Waste and Fish Meal (10:1) was readily accepted by both species of Tilapia. T. zillii voraciously fed on Cabbage leaves, Cauliflower leaves, Chinese cabbage leaves, Cassava leaves and on the common weed Comalina sp. Though all the items mentioned above were readily accepted by T. zillii feeding with Comaltna sp. was the easiest and most convenient because of its availability. In an intensive feeding experiment with vegetable leaves/Comalina sp. and the locally prepared supplimentary feed the fishes attained table size in four months time. Cement cistens of 5 X 3 X 1½ m size could be conveniently used for breeding both species of Tilapia. T. zillii had semi adhesive eggs and they were deposited on the sides of the cement wall. The number of young ones in a brood ranged from 160 to 314 in T. esculenta and 687 to 4,356 in T. zillii.

Hybridization between Tilapia zillii (Gervais) and Tilapia andersonii (Casteinau) at the Freshwater Fisheries Institute, at Nyegezi, Tanzania

As a part of an overall project on fishculture development techniques in Tanzania, hybridization between Tilapia zillii and Tilapia andersonii was carried out at the Freshwater Fisheries Institute, Nyegezi, Tanzania. T. andersonii, a plankton feeder, is not indigenous to Tanzania but was introduced in 1968 from Zambia for certain specific purpose. T. zillii, a macrovegetation feeder, is present locally and is common. In the present studies T. zillii (245.0 mm/260.0 g) female was hybridized with T. andersonii (288.0 mm/350.0 g) male. Under cement cistern conditions it was only after about four months of acclimatization that hybridization between the two occurred. About 1,637 interspecific hybrid fry were produced in a single brood. Eggs were adhesive and parental care shown by the female, the male being driven away. Growth under cistern conditions was slow, attaining a size of 134.8 mm/44.3 g in 10 months. But this growth rate need not be taken as ideal. In body shape, colouration and other morphometric characters the hybrids had inherited from both parents. The number of gill rakers among the hybrids was eighteen which was intermediate between T. zillii (12) and T. andersonii (27). Among one hundred and seventy two specimens (106.0 mm - 168.0 mm) cut and examined the sex ration was hundred per cent males and all of them were between II and IV stages of maturity. This is the first report of fish hybridization from Tanzania and possibly the first report on hybridization between T. zillii and T. andersonii. The full significanoe of the findings and its role in African fishculture is discussed.