Larval fish assemblages and geostrophic circulation in Bahia de La Paz and the surrounding southwestern region of the Gulf of California

We analyze spatial–temporal relationship between larvalfish assemblages and geostrophic surface flow in Bahíade La Paz and the neighboring Gulf of California (May, Julyand October 2001 and February 2002). The analysis of fish larvaedistribution in relation to geostrophic circulation and hydrographyis an innovative interdisciplinary approach for the understandingof fish larvae ecology. The Bray–Curtis Index definedtwo larval fish assemblages with spatial–temporal variations:coastal assemblage dominated by epipelagic coastal species (e.g.Sardinops caeruleus) and oceanic assemblages—oceanic andtransitional oceanic assemblages both dominated by mesopelagicspecies (e.g. Vinciguerria lucetia and Benthosema panamense)but with different larval abundance. The assemblage variationsappear to be related to water exchange between the bay and theGulf through the North Mouth. During July–October, thegeostrophic flow through the entrance is strong, and the oceanicassemblages spread in the whole bay, whereas during February–Maywhen the geostrophic transport is weak, the coastal assemblageis distributed over the whole bay. The strong summer–autumnwater interchange between bay and gulf is in agreement withthe annual evolution of the surface water properties insidethe bay, from high-salinity Gulf of California Water duringwinter–spring to fresher Tropical Surface Water duringsummer–autumn, when the highest species number was recorded.     

Inhibition of DNA amplification in marine fish larvae preserved in formalin

Recent advances in molecular biology open the possibility touse formalin-preserved specimens stored in ichthyoplankton collectionsfor population genetics studies. Nine DNA extraction techniqueswere tested on Engraulis mordax larvae preserved in bufferedformalin. However, none of the DNA extracts resulted in thepositive amplification of mitochondrial DNA (mtDNA) (NADH1,16srRNA, 12srRNA and control region fractions). An experimentwith different length-time exposure to formalin done with Cynoscionparvipinnis larvae allowed us to confirm the difficulty of amplifyingmtDNA from larvae preserved in formalin for long time periodsand the possibility of DNA extraction and amplification fromshort-term (less than 48 h) formalin-fixed marine fish larvaepreserved in ethanol (70%). We discuss the possible influenceof physical–chemical complexes associated with the durationof preservation to inhibition of amplification reactions.