Effect of Stocking Density on Growth Performance of Hybrids of Oreochromis niloticus♀ and Oreochromis urolepis urolepis♂ in Saline Water

Fingerlings of Oreochromis niloticus♀ and Oreochromis urolepis urolepis♂ hybrids were reared at stocking densities of control, 5, 10, 15 and 20 fish/m3 at 15 Practical Salinity Units (PSU) in 1m3 plastic tanks for 63 days. They were kept at low, intermediate and high densities respectively. All hybrids were fed on a formulated, balanced diet consisting of 40% crude protein, at a ratio of 5% body weight, twice daily. Low stocking density showed better growth performance in terms of mean weight gain, specific growth rate (SGR), feed conversion ratio (FCR) and survival rate, than intermediate and high stocking densities. SGR, FCR and survival rates did not vary significantly between treatments (p>0.05). Average final weight gain was significantly different between intermediate and high densities (p<0.05), high and low densities, but not in low and intermediate densities. Density was found to have an effect on the growth of the juvenile hybrids, since higher growth was recorded at low stocking densities compared to the intermediate and high densities. Hybrids were 100% male when inspected. The low and intermediate densities are therefore recommended for hybrids aquaculture in brackish water with the latter being suggested due to its higher yield compared to the low stocking density.

Comparison of Seaweed Growth, Fish Abundance and Diversity in Deep Water Floating Raft with Tubular Nets and Shallow Water Off-bottom lines Seaweed Farms

This study compared the growth performance of Eucheuma denticulatum, fish abundance anddiversity between deep water (using tubular nets) versus shallow water (off-bottom) seaweedfarming methods. For each farming method, three plots were set and fish abundance, diversity andseaweed growth rates were measured at intervals of 15 days. Belt transects measuring 10 m x 4 meach, were established on seaweed farms for fish observations. Fish were identified to the lowestpossible taxonomic level by underwater census. The results showed that the growth rate of E.denticulatum in deep water farms was slightly higher at an average daily growth rate (DGR) of3.42 ± 0.18% day−1 compared with 3.01 ± 0.27% day−1 for shallow water farms but with nosignificant differences (p = 0.079) likely due to higher herbivory in the deep water farms. Fishabundance and diversity were higher in deep water farms but insignificant (t (34) = 0.69, p = 0.49and t (34) = 0.424, p = 0.67, respectively). Habitat complexity and seaweed growth rate were almostsimilar for both farming methods hence attracting comparable numbers of fish. Further studies arerecommended on fish community structures, differences between the two farming methods andeffects of herbivory. Keywords: E. denticulatum; seaweed farming methods; growth; fish diversity and abundanc

Determination of Dichlorodiphenyltrichloroethane (DDT) and metabolites residues in fish species from Eastern Lake Tanganyika

In this study, the levels and status of dichlorodiphenyltrichloroethane (DDT) residues in fish samples collected from Eastern Lake Tanganyika were investigated. The analytes were determined using gas chromatography equipped with an electron capture detector (GC–ECD) and by gas chromatography-mass spectrometry (GC-MS). The compounds p,p’-DDE (4,4’-DDE), p,p’-DDD (4,4’-DDD), o,p’-DDT (2,4’-DDT) and p,p’-DDT (4,4’-DDT) were detected in all the samples, with total DDT concentrations ranging from 23 ± 8.3 to 339 ± 27 μg kg–1 fresh weight and 1736 ± 1388 μg kg–1 to 25 552 ± 4241 μg kg–1 lipid weight. The highest concentrations of total DDT were detected in Lates stappersii species. The ratios of the metabolites (DDD + DDE) to the parent compound (p,p’-DDT) were low (< 1) in all the fish samples, indicating exposure to fresh DDT. The concentrations of the DDT residues exceeded the extraneous maximum residue limit of 1.0 μg kg–1, indicating risks and concerns for public health and the environment because of the indication of fresh application of banned pesticides and bioaccumulation. There is need for continued monitoring of the residues in Lake Tanganyika environs and controlling the pesticides used in the area.Keywords: Pesticides, DDT, fish, lake, Tanzani

The Need of a Structured Tilapia Breeding Program in Tanzania to Enhance Aquaculture Production: A Review

Breeding programs are crucial for boosting productivity and increase sustainability of aquaculture. Over years, Tanzania has witnessed fluctuation in its capture fisheries production from 320,900 to 375, 535 and back to 362,595 metric tonnes in the years 2000, 2005 and 2016, respectively (URT 2016). The declining trend in fish production has made fish supply in the country unstable and conversely, increased the demand for fishes to about 730,000 metric tonnes in 2017. However, the local aquaculture production has not increased accordingly. Tanzania is importing fish mainly from Asia to meet its increased demand. In 2017, a total of 2,055,721 kg of frozen tilapia were imported from China and Mozambique (URT 2017). The introduction of exotic fish species in Tanzania should be carefully managed because introduced species have many negative impacts to the indigenous species. Tanzania should have a moderate scale tilapia breeding program that will produce good quality fingerlings at affordable price for smallholder fish farmers. The availability of reliable good quality fingerlings is key to improve aquaculture production in the country. Among 17 existing hatcheries, only 12 hatcheries are active, however these hatcheries are not performing well due to low investment and technology leading to the production of low quantity and quality fingerlings. The need for a structured sustainable Tilapia breeding program with bio secured and reliable hatcheries to enhance aquaculture production in Tanzania is given in this review.Keywords: Aquaculture, Breeding programs, Nile tilapia, Local strains

Community Based Milkfish Farming in Tanzania

In the 1990s experimental integrated mariculture of finfish, shellfish and seaweeds in a flow through system was developed to investigate bio-filtration in the ponds. The project supported mainly by WIOMSA culminated in a stakeholders’ workshop in 2004 translating the results of the experiment to community based projects. The finfish tested were milkfish (Chanos chanos), rabbit fish (Siganus canaliculatus and S. sutor), mullet (Mugil cephalus) and Zanzibar tilapia (Oreochromis urolepis hornorum). Before the workshop there were 3 milkfish mariculture ponds in Tanzania one of which was established by IMS. Following the workshop, pond finfish mariculture took off in the coastal Tanzania. In 2006, the first commercial type farm at Bagamoyo produced 1 MT/ha/yr, earning the group 2000 USD. Ever since, finfish farming has spread to all coastal districts with the highest production of 7.5 MT/ha/yr at Ndumbwe Mtwara in 2011. In 2011, trials of tilapia acclimatization and farming in estuarine and full strength sea water were started where survival and growth rates of fry and fingerlings of 4 species of tilapia were tested.

Spirulina (Arthrospira fusiformis) as a potential protein source in practical diets for fry mariculture of Rufiji tilapia (Oreochromis urolepis urolepis)

The effects on growth performance, feed utilization, survival and whole fish body proximate composition of replacing fishmeal (Rastrineobola argentea) with a locally available spirulina species (Arthrospira fusiformis) as a protein ingredient in the feed of Rufiji tilapia (Oreochromis urolepis urolepis) fry was examined. Fishmeal replacement with A. fusiformis was carried out at 5%, 15%, 25%, 35% and 100% (S5, S15, S25, S35 and S100), and the effect of the replacement was compared with the control diet (S0, 0% spirulina). Fish fry were stocked at an average initial weight of 0.57 g at 10 fish per 0.1 m3 and cultured for 60 days using full strength salt water (30-35 ppt). A. fusiformis was isolated from Momela Lake in Arusha National Park, Tanzania and propagated using selected culture media. It was observed that fish fry fed spirulina at a 5% fishmeal substitution level diet had better (p<0.05) final weight (8.48), average daily weight gain (0.132), specific growth rate (4.47), feed conversion rate (2.08) and protein efficiency ratio (1.37) compared to the control fish group. Growth performance in fish fed diet S15 was comparable with the control group (p>0.05). Spirulina supplementation had no effect on fish survival rates and meat quality. It appears that the Momella Lake spirulina may be an appropriate growth-stimulating plant protein when used as a feed additive in Rufiji tilapia mariculture.

Effect of Salinity on the Survival and Growth of Rufiji Tilapia (Oreochromis urolepis urolepis) Fry

AbstractSurvival and growth of Rufiji tilapia (Oreochromis urolepis urolepis) fry were determined under controlled salinity conditions of 5, 15, 25 and 35 ppt for 56 days. Experiments were carried out in 12 concrete tanks of 1 m3 volume each with three replicates for each treatment. Data was recorded at fourteen days intervals where weight measurements (g) of fry were recorded to the nearest 0.01 g. One Way Analysis of Variance (ANOVA) was used for data analysis. Results showed significant differences in the final body weight, specific growth rate, weight gain and daily growth rate at different salinity levels. The fry reared at a salinity of 25 ppt had the highest final body weight, specific growth rate, weight gain and daily growth rate, while the lowest was recorded at the salinity of 5 ppt. There was no significant difference in survival rate among the fry reared at different salinity levels. Dissolved oxygen (DO) was significantly different at different levels of salinity but temperature and pH showed no significant differences. The results suggest that under proper management, Rufiji tilapia can be farmed in brackish and sea water by coastal communities along the coast.

Nutrient and Bacteria Concentrations in the Coastal Waters off Zanzibar Town

AbstractsThis study assessed the concentrations and distribution of nutrients (ammonium, nitrate, nitrite, soluble reactive phosphorous) and bacteria (total and faecal coliforms) in the waters off Zanzibar Town. The study covered both the SE and NE monsoon and the two transition periods for a total of one year. Nutrient concentrations near a sewage outlet in the Bwawani area and Port sites showed values that exceeded concentrations considered acceptable for healthy reef ecosystems. The mean concentrations of total coliforms were within the ranges reported previously in the area, but faecal coliform concentrations were comparatively higher. Stations close to a sewage outlet showed the highest mean concentrations of contaminants compared to those further from the pollution source. Stations located in the shallow waters off Bawe and Changuu Islets showed slightly higher mean values compared to those located in the deeper waters between Zanzibar Town, and Bawe and Changuu Islets, which showed lowest mean values. The study has shown that the surface coastal waters off Zanzibar Town are contaminated with nutrients and coliforms due to raw sewage effluents from the Zanzibar Municipality and the distribution of these contaminants are mainly determined by seasonal monsoon winds. Therefore, there is an urgent need to treat the waste before discharging it into the coastal waters.

The trophic structure of fish in seaweed farms, and adjacent seagrass and coral habitats in Zanzibar, Tanzania

Coral reefs, seagrasses and seaweed farms (Eucheuma denticulatum) are characteristic habitats in many parts of the coast of Zanzibar, Tanzania. However, information on trophic interactions, movements of fish, and variation in fish diet specialization between these habitats are scarce. The present study determined the trophic structure and the variation in diet composition of fish caught in (floating) seaweed farms, and in adjacent seagrass and coral reef habitats in Pongwe, Zanzibar. Fish were caught using traditional basket traps (dema) and gut contents of 392 fish were analyzed. A one-way Analysis of Similarities (ANOSIM) showed that there was a significant difference in the composition of prey items eaten by invertivores in different habitats (Global R = 0.109, p = 0.002.). There was no significant difference in the composition of prey items eaten by herbivores, invertivore-piscivores and omnivores (p > 0.05), likely due to movement of fish between these habitats for foraging. There was no significant difference in the relative proportion of trophic groups between the habitats (p > 0.05) except for herbivores (p < 0.05). Floating seaweed farms attract invertebrates and smaller fish, thus providing feeding grounds for predatory fish, and should be considered as ecologically important habitats as are coral reefs and seagrass beds