The stock of the Senegalese flat sardinella, Sardinella maderensis, is highly exploited in Senegal, West Africa. Its growth and reproduction parameters are key biological indicators for improving fisheries management. This study reviewed these parameters using landing data from small-scale fisheries in Senegal and literature information dated back more than 25 years. Age was estimated using length-frequency data to calculate growth parameters and assess the growth performance index. With global climate change there has been an increase in the average sea surface temperature along the Senegalese coast but the length-weight parameters, sex ratio, size at first sexual maturity, period of reproduction and condition factor of S. maderensis have not changed significantly. The above parameters of S. maderensis have hardly changed, despite high exploitation and fluctuations in environmental conditions that affect the early development phases of small pelagic fish in West Africa. This lack of plasticity of the species regarding of the biological parameters studied should be considered when planning relevant fishery management plans.

A review of the literature shows the uncommon occurrence of this type of tumor. A few rare cases were reported among which two involving the parapharyngeal space.

Kinetic and equilibrium studies show that typical xenicanes such as dictyolactone (1) and 4-hydroxydictyolactone (3) undergo slow conformation medium-ring flipping between the predominant trans-(la or 3a; Me(20) trans to H-C(3)) and the minor cis-conformers (lb or 3b; Me(20) cis to H-C(3); see Scheme I ) . The formation of the latter is inhibited in heterocyclic-ring-opened congeners such as 18-acetoxy-4-hydroxydictyo-19-al(7). Molecularmechanics calculations suggest that typical-xenicane cis-conformers are disfavoured by mainly C(4)-C(5) torsional strain. This is confirmed by the observation of two sizably populated cis-and trans-conformers for the unnatural Coxoxenicanes 10-12. Unusually facile thermal ( E ) + ( Z ) isomerization of xenicanes 1,3,10-12, and 7 is also observed (+ 13-17 and 9, resp.; Scheme 3), reflecting great strain relief in the transition state. Conflicting results in the literature now tit into this scheme which provides a basis for unravelling recognition phenomena with these biologically active systems.1. Introduction. -Xenicane diterpenes are widespread constituents of tropical alcyonarians and gorgonians, other than of brown seaweeds in the order Dictyotales from temperate waters and sea hares that feed on them. Central examples are dictyolactone (1) [ 11, isodictyohemiacetal (2) [2a], and 18-acetoxy-4-hydroxydictyo-19-a12)In agreement with the X-ray structures [la], both 1 and 4-hydroxydictyolactone (3) were described as single conformers l a and 3a (as deduced from NMR spectra in solution) that have H-C(3) and Me-C(6) orthogonally to the mean plane of the cyclononadiene ring. These results have largely satisfied the scientific community, except for marginal notes concerning the dynamic NMR for the structurally related dictyotalide A (4) [4a] and the xeniaphyllane antheliolide A [4b, c]')"). This is quite surprising in view of

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