A peek into the population genetics of white teatfish (Holothuria fuscogilva) of Kenya's south coast.

BACKGROUND: The white teatfish, Holothuria fuscogilva, is widely distributed in coastal areas, including waters around coral reefs and seagrasses in the Indo-Pacific. In Kenya, the species is distributed in shallow reefs with higher landings reported from the Vanga-Shimoni-Gazi seascape on the Kenyan south coast. Despite its high exploitation for export and its vulnerable and endangered statuses under IUCN and CITES respectively, Kenya's H. fuscogilva populations and how they may have been impacted by the fishing pressure have not been studied. METHODS: We estimated the genetic diversity and structure of H. fuscogilva population conveniently sampled from three sites in Kenyan south coast using the mitochondrial cytochrome oxidase subunit I (COI) gene sequences. We recorded 30 haplotypes with 43 polymorphic sites across the population. Furthermore, we estimated an overall high haplotype diversity and low nucleotide diversity of estimates of h = 0.970 ± 0.013 and π = 0.010 ± 0.001 respectively. CONCLUSIONS: These preliminary findings suggest several population outcomes, among them a fit population, which require confirming with more comprehensive study to inform strategies for the sustainable exploitation and management of the species.

Nanopore metatranscriptomics reveals cryptic catfish species as potential Shigella flexneri vectors in Kenya.

Bacteria in the Shigella genus remain a major cause of dysentery in sub-Saharan Africa, and annually cause an estimated 600,000 deaths worldwide. Being spread by contaminated food and water, this study highlights how wild caught food, in the form of freshwater catfish, can act as vectors for Shigella flexneri in Southern Kenya. A metatranscriptomic approach was used to identify the presence of Shigella flexneri in the catfish which had been caught for consumption from the Galana river. The use of nanopore sequencing was shown to be a simple and effective method to highlight the presence of Shigella flexneri and could represent a potential new tool in the detection and prevention of this deadly pathogen. Rather than the presence/absence results of more traditional testing methods, the use of metatranscriptomics highlighted how primarily one SOS response gene was being transcribed, suggesting the bacteria may be dormant in the catfish. Additionally, COI sequencing of the vector catfish revealed they likely represent a cryptic species. Morphological assignment suggested the fish were widehead catfish Clarotes laticeps, which range across Africa, but the COI sequences from the Kenyan fish are distinctly different from C. laticeps sequenced in West Africa.

Movement ecology of black marlin Istiompax indica in the Western Indian Ocean.

The black marlin Istiompax indica is an apex marine predator and is susceptible to overfishing. The movement ecology of the species remains poorly known, particularly within the Indian Ocean, which has hampered assessment of their conservation status and fisheries management requirements. Here, we used pop-up archival satellite tags to track I. indica movement and examine their dispersal. Forty-nine tags were deployed off Kenya during both the north-east (November-April) and south-west (August-September) monsoon seasons, providing locations from every month of the year. Individual I. indica were highly mobile and track distance correlated with the duration of tag attachment. Mean track duration was 38 days and mean track distance was >1800 km. Individuals dispersed in several directions: north-east into Somalian waters and up to northern Oman, east towards the Seychelles, and south into the Mozambique Channel. Their core habitat shifted seasonally and overlapped with areas of high productivity off Kenya, Somalia and Oman during the first half of the year. A second annual aggregation off the Kenyan coast, during August and September, did not coincide with high chlorophyll-a (chl-a) concentrations or thermal fronts, and the drivers of the species' presence and movement from this second aggregation was unclear. We tested their habitat preferences by comparing environmental conditions at track locations to the conditions at locations along simulated tracks based on the empirical data. Observed I. indica preferred cooler water with higher chl-a concentrations and stayed closer to the coast than simulated tracks. The rapid and extensive dispersal of I. indica from Kenya suggests that there is likely a single stock in the Western Indian Ocean, with individuals swimming between areas of high commercial catches off northern Somalia and Oman, and artisanal and recreational fisheries catches throughout East Africa and Mozambique.

Movement and habitat use of striped marlin Kajikia audax in the Western Indian Ocean.

Striped marlin Kajikia audax are globally Near Threatened and their stock in the Indian Ocean was last assessed as "overfished and subject to overfishing". Significant gaps in our understanding of their ecology remain, hampering the efforts of fisheries managers to ensure stock sustainability. There is a particular lack of fisheries-independent data. Here we present the results from the first large-scale satellite tracking study of K. audax in the Indian Ocean. We tagged 49 K. audax with pop-up archival satellite-linked tags off the Kenyan coast from 2015 to 2019. Individuals were highly mobile, covering horizontal distances of up to 9187 km over periods ranging up to 183 days, with a mean daily distance of ~48 km. Long-distance movements were recorded to the east and north of East Africa, with the most distant tracks extending north to the Arabian Sea and east to near the Maldives. None of the K. audax swam south of East Africa. Kernel utilization distributions of fish locations demonstrated their shifting seasonal activity hotspots. Over the sport-fishing season (and tagging period) in Kenya, from December to March, K. audax typically stayed off the East African coast. After March, the activity hotspot shifted north to a region close to the Horn of Africa and Socotra Island. Remotely sensed sea surface temperature and chlorophyll-a maps indicated that this seasonal movement could be driven by a shift in prey availability. Our results show the high mobility of K. audax in the Western Indian Ocean, and that individuals seasonally range between two major fishing areas.

Investigating a simplified method for noninvasive genetic sampling in East African mammals using silica dried scat swabs.

Swabbing scat has proved to be an effective noninvasive method to collect DNA from mammals in the field. Previously, this method has relied on preservative liquids or freezing to preserve the DNA collected on swabs. In this study, we determine the effectiveness of using silica to simply dry the swab in field as an alternative way to prevent DNA degredation. Four species were included in the study; reticulated giraffe, impala, fringe-eared oryx, and lion. Swabs were taken at multiple time points for giraffe and impala scat samples, with the lion and oryx sampled opportunistically. Mitochondrial DNA was successfully amplified and sequenced from scat swabs from all species; however, effectiveness varied between species, with 81.8% amplification success rate from swabs taken from impala scat compared to 25% amplification success rate in giraffe. This variation in success rate was overcome by taking multiple swabs, thus increasing the probability of a successful amplification. The true merit of this method is in its simplicity and cheapness; no preservative liquids were required to be brought into the field, at no stage in the 2 weeks of field sampling were samples frozen, and no commercial kits were used for DNA extraction.

A preliminary observation on water quality and plankton of an earthen fish pond in Bangladesh: recommendations for future studies.

The present study provides a characterization of water quality and plankton samples in earthen fish pond in Rajshahi, Bangladesh. Sampling was done over a period of six months, running from October, 2004 through March, 2005. All the water quality parameters were within the optimal ranges for plankton productivity. Temperatures varied from 19.75 to 27.25 degrees C; transparency, 24.75-29.50 cm; pH, 6.62-7.85; Dissolved Oxygen (DO), 3.87-5.85 mg L(-1); free CO2 5.25-7.25 mg L(-1) and bicarbonate (HCO3) alkalinity, 81.25-147.5 mg L(-1). Analyses of plankton samples recorded a total of 5 classes phytoplankton viz.; Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Euglenophyceae and 2 classes of zooplankton; Crustacea and Rotifera. The phytoplankton population was comprised of 17 genera belonging to Cyanophyceae (5 classes, 34.47%), Bacillariophyceae (3, 13.87%), Cyanophyceae (3, 34.48%), Euglenophyceae (3, 10.68%) and 1 to Dinophyceae (6.50%). The zooplankton population consisted of 10 genera belonging to Rotifera (4, 40.13%) and Crustacea (6, 59.87%). Phytoplankton and zooplankton abundance varied from 60800 to 239400 units/l and 7620 to 12160 units/l, respectively. It is concluded that the phytoplankton groups provide the main support for earthen pond aquaculture in the pond compared to zooplankton classes. The information provides for more research to compare water quality and pond plankton characteristics in earthen aquaculture systems with and without fish stocking. Further studies on the seasonal changes of water quality parameters and its effects on plankton production in the fish ponds and all year extended monitoring is recommended in future studies.