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Establishing suitable salt tolerant all-male tilapia strains with fast growth rate is a crucial requirement for successful euryhaline farming required for controlling prolific breeding and as an adaptation to the effect of climate-induced drought. This study assessed the percentage of tilapia male hybrids, their growth performance and survival rate produced by crossing female Nile tilapia (Oreochromis niloticus) and male Rufiji tilapia (Oreochromis urolepis urolepis) at different salinities. The fingerlings were reared for 70 days in triplicate concrete tanks (1 m3), each stocked with 15 fish weighing 1.62 ± 0.03 g, 1.69 ± 0.02 g and 1.41 ± 0.06 g exposed to 2, 15 and 35 ppt salinities, respectively. Acclimatization was done by adding seawater to freshwater at a rate of 2 ppt per day for 18 days. Fish sexing was done by visual assessment of the genital papilla followed by rearing the hybrids for six months to observe reproduction. Results showed that, the cross between O. niloticus (female) and O. urolepis urolepis (male) produced hybrids that were all-males without any reproduction within six months post hybridization. The hybrids reared at a salinity of 2 ppt had higher growth performance than those reared at 15 and 35 ppt. Similarly, hybrids cultured at 15 ppt had significantly higher growth performance than those reared at 35 ppt. All the hybrids produced had survival rates of 100%. This study indicated that, all-male tilapia produced by crossing between O. niloticus (female) and O. urolepis (male) can be used by fish farmers as alternative species for mariculture development to control prolific breeding and as an adaptation strategy to climate change.

The study examined different types of organic manure on the culture of marine plankton as a potential source of food for rabbitfish, Siganus stellatus, larvae. Cow dung showed significantly higher species abundance and diversity of cultured marine plankton followed by chicken and finally mixed media manure (p

Climate change‐induced ocean warming is expected to greatly affect carbon dynamics and sequestration in vegetated shallow waters, especially in the upper subtidal where water temperatures may fluctuate considerably and can reach high levels at low tides. This might alter the greenhouse gas balance and significantly reduce the carbon sink potential of tropical seagrass meadows. In order to assess such consequences, we simulated temperature stress during low tide exposures by subjecting seagrass plants (Thalassia hemprichii) and associated sediments to elevated midday temperature spikes (31, 35, 37, 40, and 45°C) for seven consecutive days in an outdoor mesocosm setup. During the experiment, methane release from the sediment surface was estimated using gas chromatography. Sulfide concentration in the sediment pore water was determined spectrophotometrically, and the plant's photosynthetic capacity as electron transport rate (ETR), and maximum quantum yield (Fv/Fm) was assessed using pulse amplitude modulated (PAM) fluorometry. The highest temperature treatments (40 and 45°C) had a clear positive effect on methane emission and the level of sulfide in the sediment and, at the same time, clear negative effects on the photosynthetic performance of seagrass plants. The effects observed by temperature stress were immediate (within hours) and seen in all response variables, including ETR, Fv/Fm, methane emission, and sulfide levels. In addition, both the methane emission and the size of the sulfide pool were already negatively correlated with changes in the photosynthetic rate (ETR) during the first day, and with time, the correlations became stronger. These findings show that increased temperature will reduce primary productivity and increase methane and sulfide levels. Future increases in the frequency and severity of extreme temperature events could hence reduce the climate mitigation capacity of tropical seagrass meadows by reducing CO2 sequestration, increase damage from sulfide toxicity, and induce the release of larger amounts of methane., In order to estimate responses to warming in seagrass sediments, a mesocosm experiment with tropical seagrasses was performed. We measured methane release, sulfide concentration in the sediment pore water, and the plant's photosynthetic capacity. The higher temperatures had clear negative effects on the photosynthetic performance of seagrass plants and, at the same time, a clear positive effect on methane emission and the level of sulfide in the sediment. Future increases in the frequency and severity of extreme temperature events could hence cause tropical seagrass meadows to suffer increased damage from sulfide toxicity and induce the release of larger amounts of methane.

An investigative field survey was performed to gather baseline data on locally available feed ingredients and fish farming practices in different regions of Tanzania. More than 80% of respondents relied on locally available feed ingredients as a major feed supplement for their cultured fish, with maize bran being the most commonly used feed ingredient in all regions. Crude protein content in most analyzed local feed ingredients was medium-high, while crude fat content was high in some animal and agricultural by-products, and medium-low in other ingredients. Most respondents were males and the majority of fish farms were owned by individuals. Earthen pond was the most common fish farming system in all regions except Dar es Salaam. Semi-intensively mixed-sex tilapia monoculture was the dominating fish farming practice. The results of the survey presented provide a good platform for future development of culture systems and feeding strategies for tilapia in Tanzania.

Tropical seagrass meadows are formed by an array of seagrass species that share the same space. Species sharing the same plot are competing for resources, namely light and inorganic nutrients, which results in the capacity of some species to preempt space from others. However, the drivers behind seagrass species competition are not completely understood. In this work, we studied the competitive interactions among tropical seagrass species of Unguja Island (Zanzibar, Tanzania) using a trait-based approach. We quantified the abundance of eight seagrass species under different trophic states, and selected nine traits related to light and inorganic nutrient preemption to characterize the functional strategy of the species (leaf maximum length and width, leaves per shoot, leaf mass area, vertical rhizome length, shoots per meter of ramet, rhizome diameter, roots per meter of ramet, and root maximum length). From the seagrass abundance we calculated the probability of space preemption between pairs of seagrass species and for each individual seagrass species under the different trophic states. Species had different probabilities of space preemption, with the climax species Thalassodendron ciliatum, Enhalus acoroides, Thalassia hemprichii, and the opportunistic Cymodocea serrulata having the highest probability of preemption, while the pioneer and opportunistic species Halophila ovalis, Syringodium isoetifolium, Halodule uninervis, and Cymodocea rotundata had the lowest. Traits determining the functional strategy showed that there was a size gradient across species. For two co-occurring seagrass species, probability of preemption was the highest for the larger species, it increased as the size difference between species increased and was unaffected by the trophic state. Competitive interactions among seagrass species were asymmetrical, i.e., negative effects were not reciprocal, and the driver behind space preemption was determined by plant size. Seagrass space preemption is a consequence of resource competition, and the probability of a species to exert preemption can be calculated using a trait-based approach.

Snubnose pompano (Trachinotus blochii) are widely cultured in the world. Light colours are among factors affecting fish performance in captivity. Snubnose pompano larvae often reared under white light. However, no study supports its choice or informs the extent of its effect or its constituent colour. The study investigated the influence of green, blue, yellow, purple, and white lights on growth, survival, cortisol, body composition, and digestive enzymes activities of one-day post-hatch Snubnose pompano larvae reared in light magenta tanks under a photoperiod of 24 Light:0 Dark hours for 25 days. Overall, the best growth performance of snubnose pompano larvae was in purple and white, and green lights during early and late larval stages, respectively. White light promoted survival rate while that of green light reduced. Larvae were less stressed and had enhanced body contents under white and purple light environments. Purple and yellow lights influenced low trypsin and pepsin activities. The study reports for the first time the effect of the light colour environment on the digestive enzyme activities and body composition of the finfish larvae. Generally, the study provides novel insights on optimal light colour in the larval rearing protocol of this species. Through this study, the use of white light during the first feeding (zero to four days post-hatch) and purple light in later stages (five days post-hatch until metamorphosis) is encouraged while discourages green and yellow lights in the larval rearing of Snubnose pompano.

An investigation of the role of Lactobacillus plantarum and Saccharomyces cerevisiae on growth performance of hybrids from Oreochromis niloticus and Oreochromis urolepis urolepis was carried out in plastic tanks at 10 fish/m3 density and a salinity of 25 units. The probiotic treatments were 2, 4 and 6 g/kg feed while the control feed did not include any probiotics. Growth parameters were measured fortnightly and water quality parameters monitored every day. Survival rate and water quality factors revealed non-significant variations (p > 0.05). Final weight differed significantly among the treatments (p < 0.05). Furthermore, Food Conversion Ratio (FCR), Specific Growth Rates (SGR), and weight gain did not differ significantly (p > 0.05) between the control and 2 g/kg treatments. However, the 4 and 6 g/ kg feed treatments showed significant differences (p < 0.05) from the control diet and 2 g/kg for both L. plantarum and S. cerevisiae. The condition factor did not show any significant difference (p > 0.05) among the treatments. Results of this study indicate that increasing the quantity of commercial probiotics in feeds improved growth rates. Condition factor observed in the treatments could be due to the role of the tested probiotics in improving the water quality of tanks. Therefore, probiotics could potentially be used to enhance coastal aquaculture development.

Tilapia hatcheries in Tanzania rely heavily on importing germplasm. Nevertheless, the genetic structure of the imported stocks is poorly understood. In the current study, the level of genetic diversity and differentiation of eight populations of Nile tilapia (Oreochromis niloticus) strains imported in Tanzania was investigated. Four of the studied strains originated from Thailand, three from Uganda, and one from the Netherlands. Double-digest restriction site–associated DNA sequencing (ddRAD-seq) was applied to identify and genotype single nucleotide polymorphisms (SNPs). In total, 2214 SNPs passed all the quality control steps and were utilized for downstream analysis. Mean heterozygosity estimates were higher for the Thailand strains (Ho, 0.23) compared with the strains from Uganda (Ho, 0.12). Low genetic distance was observed amongst populations from the same geographic origin (Fst, 0.01–0.04). However, genetic distance between populations from different geographic origins was substantial (Fst, 0.24–0.44). Bayesian model–based clustering (STRUCTURE) and discriminant analysis of principal components (DAPC) grouped the studied animals into three distinct clusters. A cross-validation approach (where 25% of animals from each population were considered of unknown origin) was conducted in order to test the efficiency of the SNP dataset for identifying the population of origin. The cross-validation procedure was repeated 10 times resulting in approximately 97% of the tested animals being allocated to the correct geographic population of origin. The breeding history and hatchery practices used to manage these stocks prior and after import appear to be the main factors for the genetic diversity observed in this study. Our study will help inform hatchery stock management and future breeding program designs in Tanzania.

Five introduced strains of Nile tilapia (Oreochromis niloticus) were tested for growth performance both in fresh- and brackish-water (2 salinity units) environments for 56 days. The BIG NIN, GIFT, Chitralada, “Ruvu Farm” and Silver YY strains with initial mean average weight (± standard error) of 96.4 ± 6.90 g, 104.1 ± 7.19 g, 137.2 ± 7.21 g, 53.2 ± 6.98 g and 95.3 ± 7.11 g, respectively were used. Individuals were tagged and pooled in hapas (12 m × 8.5 m × 2 m each), aligned into different ponds (20 m × 20 m each). Stocking density of 5 fish/m2 and 350 g/kg crude protein diet were used. Overall, the average weight gain for GIFT strain was 7.5%, 32%, 45% and 86.5% higher than BIG NIN, Chitralada, “Ruvu Farm” and Silver YY strains, respectively, across both environments. All strains performed significantly better (p

IntroductionThe decline in fishery resources from the wild has led to an ever increasing focus on aquaculture in recent years. With increasing aquaculture of animal species, there is an increasing need for suitable microalgae in the production of these animals. However, cultivation of microalgae in expensive pure chemical media is one of the major challenges facing large-scale cultivation of microalgae.PurposeThe present study investigated the suitability of aquaculture wastewater (AWW) supplemented with NPK (nitrogen:phosphorus:potassium) fertilizer as a cheap source of nutrient to cultivate a microalgaChlorella vulgaris(C. vulgaris).MethodsC. vulgariswith an initial cell density of 0.8 × 106cells/mL was batch cultured in AWW supplemented with NPK at 0.1, 0.5, 1.0 g/L and BBM for 20 days under laboratory conditions using 2000 mL Erlenmeyer flasks. The proximate composition, chlorophyll, minerals, and vitamins analysis ofC. vulgarisbiomass were done using standard analytical methods.ResultsThe highest values in optical density (4.872 ± 0.025), dry cell weight (2.858 ± 0.015 g/L), specific growth rate (0.2097 ± 0.0038 day–1), and biomass productivity (0.1701 ± 0.0007 g/L/day) were obtained inC. vulgarisgrown in AWW + 1.0 NPK medium. The total chlorophyll, protein, lipid, and carbohydrate content of the microalgae biomass were in the range of 0.05–0.862%, 44.062–57.089%, 17.064–23.260%, and 15.217–21.896%, respectively. Furthermore, microalgae grown in AWW + 1.0 NPK showed good vitamin and mineral content compared to BBM grown alga.ConclusionThese findings indicated that the AWW + 0.1 NPK, AWW + 0.5 NPK, and AWW + 1.0 NPK are potential growth media forC. vulgariscultivation and can replace the BBM medium, which is very expensive and less accessible to users.

Eight locally available protein source ingredients in Tanzania were selected for assessment of apparent digestibility (AD) in tilapia Oreochromis niloticus, using faeces samples collected by siphoning or stripping. The selected protein source ingredients were Lake Victoria sardines (FM), brewers spent yeast (BSY), moringa leaves (ML), freshwater shrimp (FSH), marine shrimp (MSH), cattle blood (CB), duckweed (DW) and fish frames (FF). The AD (%) of dry matter (DM), organic matter (OM) and crude protein (CP) was unaffected (p &gt, 0.782&ndash, 0.901) by the faeces collection method (i.e., siphoning or stripping), with correlation coefficient (r) of 0.98, 0.99 and 0.93 between AD values for DM, OM and CP, respectively, following siphoning and stripping. The AD (%) of DM, OM, CP and gross energy (GE) in the test ingredients differed (p &lt, 0.0001). The AD (%) of DM and OM was lowest in BSY and DW, followed in increasing order by ML, MSH, FF, FSH and CB. In general, the AD (%) of CP was high (&gt, 76%), but with a low value (46%) for DW. The AD (%) of GE was closely correlated (r = 0.96) with the AD of OM. In conclusion, FSH, MSH, CB, FF, BSY and ML have acceptable protein digestibility to be used in tilapia diet formulation.

Rufiji tilapia (Oreochromis urolepis urolepis) is an endemic cichlid in Tanzania. In addition to its importance for biodiversity conservation, Rufiji tilapia is also attractive for farming due to its high growth rate, salinity tolerance, and the production of all‐male hybrids when crossed with Nile tilapia (Oreochromis niloticus). The aim of the current study was to assess the genetic diversity and population structure of both wild and farmed Rufiji tilapia populations in order to inform conservation and aquaculture practices. Double‐digest restriction‐site‐associated DNA (ddRAD) libraries were constructed from 195 animals originating from eight wild (Nyamisati, Utete, Mansi, Mindu, Wami, Ruaha, Kibasira, and Kilola) and two farmed (Bwawani and Chemchem) populations. The identified single nucleotide polymorphisms (SNPs; n = 2,182) were used to investigate the genetic variation within and among the studied populations. Genetic distance estimates (F st) were low among populations from neighboring locations, with the exception of Utete and Chemchem populations (F st = 0.34). Isolation‐by‐distance (IBD) analysis among the wild populations did not detect any significant correlation signal (r = .05; p‐value = .4) between the genetic distance and the sampling (Euclidean distance) locations. Population structure and putative ancestry were further investigated using both Bayesian (Structure) and multivariate approaches (discriminant analysis of principal components). Both analysis indicated the existence of three distinct genetic clusters. Two cross‐validation scenarios were conducted in order to test the efficiency of the SNP dataset for discriminating between farmed and wild animals or predicting the population of origin. Approximately 95% of the test dataset was correctly classified in the first scenario, while in the case of predicting for the population of origin 68% of the test dataset was correctly classified. Overall, our results provide novel insights regarding the population structure of Rufiji tilapia and a new database of informative SNP markers for both conservation management and aquaculture activities., The objective of the current study was to assess the genetic variation among 10 Rufiji tilapia populations of both wild and farmed origin using ddRAD‐seq. We investigate for the existence of putative genetic clusters, test for the existence of isolation by distance, and assess the efficiency of predicting population of origin‐based only on the genomic profile using cross‐validation schemes.

Marine vegetated ecosystems such as seagrass meadows are increasingly acknowledged as important carbon sinks based on their ability to capture and store atmospheric carbon dioxide, thereby contributing to climate change mitigation. Most studies on carbon storage in marine ecosystems have focused on organic carbon, leaving inorganic carbon processes such as calcification unaccounted for, despite of their critical role in the global carbon budget. This is probably because of uncertainties regarding the role of calcification in marine carbon budgets as either atmospheric CO2 source or sink. Here, we conducted a laboratory experiment to investigate the influence of a calcifying alga (Corallina officinalis L.) on seawater carbon content, using a non-calcifying alga (Ulva lactuca L.) as a control. In a first part, algae were incubated separately while measuring changes in seawater pH, total alkalinity (TA) and total dissolved inorganic carbon (DIC). The amount of carbon used in photosynthetic uptake and production of CaCO3 was then calculated. In a second, directly following, part the algae were removed and DIC levels were allowed to equilibrate with air until the pH stabilized and the loss of CO2 to air was calculated as the difference in total DIC from the start of part one, to the end of the second part. The results showed that C. officinalis caused a significant and persistent reduction in total dissolved inorganic carbon (DIC), TA and seawater pH, while no such permanent changes were caused by U. lactuca. These findings indicate that calcification can release a significant amount of CO2 to the atmosphere and thereby possibly counteract the carbon sequestration in marine vegetated ecosystems if this CO2 is not re-fixed in the system. Our research emphasises the importance of considering algal calcification in future assessments on carbon storage in coastal areas.

Understanding population structure and genetic diversity within and between local Nile tilapia lines cultured in Tanzania is important for sustainable aquaculture production. This study investigated the genetic structure and diversity among seven Nile tilapia populations in Tanzania (Karanga, Igunga, Ruhila, Fisheries Education and Training Agency, Tanzania Fisheries Research Institute, Kunduchi, and Lake Victoria). Double-digest restriction site-associated DNA (ddRAD) libraries were prepared from 140 individual fish (20 per population) and sequenced using an Illumina HiSeq 4000 resulting in the identification of 2,180 informative single nucleotide polymorphisms (SNPs). Pairwise Fst values revealed strong genetic differentiation between the closely related populations; FETA, Lake Victoria, and Igunga and those from TAFIRI and Karanga with values ranging between 0.45 and 0.55. Population structure was further evaluated using Bayesian model-based clustering (STRUCTURE) and discriminant analysis of principal components (DAPC). Admixture was detected among Karanga, Kunduchi, and Ruhila populations. A cross-validation approach(25% of individual fish from each population was considered of unknown origin) was conducted in order to test the efficiency of the SNP markers to correctly assign individual fish to the population of origin. The cross-validation procedure was repeated 10 times resulting in 77% of the tested individual fish being allocated to the correct population. Overall our results provide a new database of informative SNP markers for both conservation management and aquaculture activities of Nile tilapia strains in Tanzania.

The effect of repeated midday temperature stress on the photosynthetic performance and biomass production of seagrass was studied in a mesocosm setup with four common tropical species, including Thalassia hemprichii, Cymodocea serrulata, Enhalus acoroides, and Thalassodendron ciliatum. To mimic natural conditions during low tides, the plants were exposed to temperature spikes of different maximal temperatures, that is, ambient (29–33°C), 34, 36, 40, and 45°C, during three midday hours for seven consecutive days. At temperatures of up to 36°C, all species could maintain full photosynthetic rates (measured as the electron transport rate, ETR) throughout the experiment without displaying any obvious photosynthetic stress responses (measured as declining maximal quantum yield, Fv/Fm). All species except T. ciliatum could also withstand 40°C, and only at 45°C did all species display significantly lower photosynthetic rates and declining Fv/Fm. Biomass estimation, however, revealed a different pattern, where significant losses of both above‐ and belowground seagrass biomass occurred in all species at both 40 and 45°C (except for C. serrulata in the 40°C treatment). Biomass losses were clearly higher in the shoots than in the belowground root–rhizome complex. The findings indicate that, although tropical seagrasses presently can cope with high midday temperature stress, a few degrees increase in maximum daily temperature could cause significant losses in seagrass biomass and productivity.