Slow growth of the overexploited milk shark Rhizoprionodon acutus affects its sustainability in West Africa.

Age and growth of Rhizoprionodon acutus were estimated from vertebrae age bands. From December 2009 to November 2010, 423 R. acutus between 37 and 112 cm total length (LT ) were sampled along the Senegalese coast. Marginal increment ratio was used to check annual band deposition. Three growth models were adjusted to the length at age and compared using Akaike's information criterion. The Gompertz growth model with estimated size at birth appeared to be the best and resulted in growth parameters of L∞ = 139.55 (LT ) and K = 0.17 year(-1) for females and L∞ = 126.52 (LT ) and K = 0.18 year(-1) for males. The largest female and male examined were 8 and 9 years old, but the majority was between 1 and 3 years old. Ages at maturity estimated were 5.8 and 4.8 years for females and males, respectively. These results suggest that R. acutus is a slow-growing species, which render the species particularly vulnerable to heavy fishery exploitation. The growth parameters estimated in this study are crucial for stock assessments and for demographic analyses to evaluate the sustainability of commercial harvests.

Spatio-temporal isotopic signatures (δ13 C and δ15 N) reveal that two sympatric West African mullet species do not feed on the same basal production sources.

Potential trophic competition between two sympatric mullet species, Mugil cephalus and Mugil curema, was explored in the hypersaline estuary of the Saloum Delta (Senegal) using δ(13) C and δ(15) N composition of muscle tissues. Between species, δ(15) N compositions were similar, suggesting a similar trophic level, while the difference in δ(13) C compositions indicated that these species did not feed from exactly the same basal production sources or at least not in the same proportions. This result provides the first evidence of isotopic niche segregation between two limno-benthophageous species belonging to the geographically widespread, and often locally abundant, Mugilidae family.

Growth hormone and Prolactin-1 gene transcription in natural populations of the black-chinned tilapia Sarotherodon melanotheron acclimatised to different salinities.

The effects of salinity on the expression of genes coding for growth hormone (GH) and prolactin-1 (PRL1) were studied in various natural populations of the black-chinned tilapia Sarotherodon melanotheron from West Africa. Individuals were sampled in June 2005 in six locations in Senegal and the Gambia, at various salinities between 0 and 101. The poorest condition factors were recorded in the most saline sampling site and the best growth in the fish from a marine environment. The pituitary GH mRNA levels were significantly higher in fish adapted to seawater, whereas the PRL1 mRNA levels were highest in fish adapted to fresh- and brackish water. These results show that the PRL1 mRNA levels seem to reflect relatively well the differences in environmental salinity, in contrast to those of GH, which would tend instead to reflect the individual growth in each environment. However, no relation could be found between growth in the hypersaline areas and the expression profile of GH. Although the fish analysed were morphologically identical, the expression of genes coding for GH and PRL1 showed large differences between individuals. This inter-individual variation in gene expression remains poorly understood.

Impact of glaciations and geographic distance on the genetic structure of a tropical estuarine fish, Ethmalosa fimbriata (Clupeidae, S. Bowdich, 1825).

We assayed the mtDNA phylogeography [196 base pairs (bp) of the cytochrome b] and population structure (n = 680) in the estuarine fish, Ethmalosa fimbriata, from its whole distribution range: 14 locations along the West African coasts were sampled. Specifically, we considered Pleistocene glaciations as well as the hydrodynamics and climatic conditions of the estuarine environments in order to identify the main evolutionary forces that have shaped the genetic variation in mtDNA, i.e., the contemporary or the historical gene flow. There was an overall significant population differentiation among estuaries (Fst = 0.10). Although E. fimbriata showed a significant pattern of isolation by distance over the entire sampled range, this genetic structure did not mirror contemporary gene flow but the colonization sequence of the present distribution range. Finally, the mtDNA genetic structure traced the past historic dispersion that occurred at the end of the Pleistocene glaciations. The central part of the present distribution area was probably the species origin and due to difference in the historic migration rate northward and southward, isolation of a South group occurred first, 110,000-190,000 years ago, before the divergence of the North group 47,000-82,000 years ago.

Ames Salmonella/mammalian-microsome testing of peptides and peptide synthesis reagents.

The Ames Salmonella/mammalian-microsome assay was used to evaluate the bacterial mutagenicity of 6 bioactive peptides and of 11 chemical reagents used in peptide synthesis. Samples of 2 reagents, bis(2-oxo-3-oxazolidinyl)phosphinic chloride and fluoren-9-ylmethyl chloroformate, showed mutagenic activity with strains TA100 and TA1535, and with TA1537, respectively. No mutagenic activity was found with the bioactive peptides or with the other 9 peptide synthesis reagents.