Description of the free-swimming juvenile stages of Lernaeocera branchialis (Pennellidae), using traditional light and confocal microscopy methods

Abstract

The last detailed morphological descriptions of the juvenile stages of the parasitic copepod Lernaeocera branchialis (L., 1767) were written more than 70 yr ago, since which time both taxonomic nomenclature and available imaging technologies have changed substantially. In this paper a re-description of the free-swimming juvenile stages of L. branchialis is presented using a combination of traditional light microscopy and modern laser scanning confocal microscopy (LSCM) techniques. Detailed descriptions are provided of the nauplius I, nauplius II and copepodid stages and comparisons are made with the findings for other siphonostomatoids. Nauplius II is previously undescribed and several structures are described at the terminal tip which have not been found in other pennellids. With renewed interest in L. branchialis as a result of expanding gadoid aquaculture in North Atlantic countries, this re-description provides important information on its life history that may be useful for further research into this potentially devastating pathogen. KEY WORDS: Parasitic Crustacea · Confocal · MorphologyResale or republication not permitted without written consent of the publisher Aquat Biol 14: 153-163, 2012 finally described more completely by Kabata (1979) and by Boxshall (1990).Taxonomic nomenclature and systematics have developed and changed considerably since Sproston's original description of the juvenile stages and technological advancements in microscopy have made it possible to study specimens in greater detail. Therefore a re-examination of the free-swimming juvenile stages is presented in this study, using a combination of both light microscopy and laser scanning confocal microscopy (LSCM). MATERIALS AND METHODSWhiting Merlangius merlangus (L.) and, to a lesser degree, cod Gadus morhua (L.) infected with Lernaeocera branchialis were sampled from the catches of commercial demersal trawlers working within the River Forth Estuary at Kincardine,Scotland (56°02'53''N, 3°40' 59'' W). To culture the juvenile stages of L. branchialis, egg strings were dissected from gravid female parasites collected from infected whiting and cod. These were then maintained under aeration in 500 ml beakers kept in a WTB Binder Labortechnik precision environmental chamber at 10°C. Once the eggs began to hatch they were placed in a beaker of fresh aerated seawater (35 ppt) and after a period of time (20 min to 24 h) the egg strings were transferred to another beaker of fresh seawater, leaving behind a 'batch' of nauplii. These batches were then used for ex periments as either nauplii or copepodids, depending on how long they were maintained (nauplius I < 20 min, nauplius II < 32 h, copepodid > 32 h).Lernaeocera branchialis specimens for traditional light microscopy were prepared by clearing individuals in 85% lactic acid (Sigma L1250) for 30 min, which also softened the connective tissues, and then by dissecting them on a cavity slide using fine mounted needles under a dissecting microscope. Individual appendages from each sp...