Identification of marine fish egg predators using molecular probes

Abstract

Mortality during the egg and larval stages is thought to play a major role in de termining year-class strength of many marine fish. Predation of eggs and larvae is normally considered to be a major factor but the full suite of predators responsible has rarely been identified. Potential predators on a patch of plaice Pleuronectes platessa eggs located in the eastern Irish Sea were mapped using acoustics and sampled by trawl and a plankton multi-net. Gut contents of 3373 fish, crustacea and cephalopods sampled in the area were screened using a plaice-specific TaqMan DNA probe. Herring Clupea harengus and sprat Sprattus sprattus dominated trawl catches and showed high positive TaqMan responses (77 and 75% of individuals tested respectively). Locations of clupeid schools also broadly corresponded with the distribution of fish eggs in the plankton. Whiting Merlangius merlangus were also reasonably abundant in trawl hauls and 86% of their stomachs tested positive for plaice DNA. Species showing lower levels of positive TaqMan response included mackerel Scomber scombrus, poor cod Trisopterus minutus, squid Loligo spp., dogfish Scyliorhinus canicula and weever Trachinus vipera. Nonre activity of all negative controls precluded the occurrence of cross-contamination, and positive reactions from demersal species, such as dogfish and weever, may have resulted from secondary predation. No benthic macro-crustaceans tested positive. Samples of planktonic organisms yielded 13% positive TaqMan reactions, mainly from clupeoid or sandeel (Ammodytidae) larvae, but also included some Malacostraca and Amphipoda. Use of the molecular approach allowed rapid screening of a large number of potential predators of plaice eggs, and the results provide a more holistic description of the predator community than has previously been achieved.

A real-time PCR assay to estimate invertebrate and fish predation on anchovy eggs in the Bay of Biscay

“…For sardine, acoustic biomasses from PELGAS 2010 campaign's ''south-offshore'' and ''Gironde'' areas were selected as they roughly corresponded to the two anchovy spawning centers in 2010. (Albaina et al, 2010Fox et al, 2012) and this was replicated here. Apart from this, other biases associated with the assessment of predation, independently of the method applied, include regurgitation, the risk of feeding within the sampling gear, scavenging and secondary predation.…”

“…Fox et al, 2005Fox et al, , 2008Minegishi et al, 2009). Examples of real-time PCR application to characterize marine animals diet include copepods (Nejstgaard et al, 2008;Troedsson et al, 2009;Durbin et al, 2008Durbin et al, , 2011, decapods (Töbe et al, 2010;Albaina et al, 2010Albaina et al, , 2012Cleary et al, 2012;Redd et al, 2014), fishes Fox et al, 2012;Baerwald et al, 2012) and mammals (Bowles et al, 2011).…”

“…Average number of eggs per predator kg during time t 0Fox et al, 2012). Dilution of template DNA combined with the addition of 1.25 lg/ll bovine serum albumin (BSA) to the PCR reaction mix has been shown as effective in overcoming PCR inhibition both in fish and marine invertebrates…”

Egg boons: central components of marine fatty acid food webs

“…Fish eggs are a component of the diet of a wide variety of planktivorous fishes, based on observations of gut contents or application of molecular probes (Fox et al 2012). The most immediate consumers of eggs are the spawners that produced them.…”

Cryptic diets of forage fish: jellyfish consumption observed in the Celtic Sea and western English Channel

“…Stomachs were removed and frozen on‐board. At a molecular laboratory, S. sprattus stomachs had DNA extracted using the salt extraction technique as described here, S. scombrus stomachs had DNA extracted using a cetyltrimethylammonium bromide (CTAB) method (Fox et al , ). PCR conditions were identical to those described here.…”