A new method to determine in situ growth rates of decapod shrimp: a case study with brown shrimp Crangon crangon

Abstract

Shrimps are economically and ecologically very important, yet a lack of ageing techniques and hence unknown growth rates often impairs analytical assessments and management. A new method for the determination of in situ growth rates of shrimps is presented, based on dry weight condition. Since this index oscillates from low values directly after moult to highest values prior to moult in constantly feeding shrimp, the lowest observed premoult condition followed by a moult was introduced as a reference value to separate growing and starving individuals in field data. Experiments with Crangon crangon confirmed that (1) post-moult condition varies in a narrow physiologically optimal range, regardless of recent growth increments, and (2) dry weight condition prior to moult is closely related to the subsequent length increment. The method was applied to estimate growth increments from in situ dry weight condition data of C. crangon. The new method can easily be applied to other related species, since the required data can be obtained from very simple shortterm experiments.

Are the RNA:DNA ratio and dry-weight-at-length suitable growth proxies for brown shrimps (<em>Crangon crangon</em>)?

“…Measurement errors of up to 10% can occur (unpublished data). Furthermore, water is permanently replaced by protein during the in-ter-moult period (Passano 1960, Perger andTemming 2012), sio wet weight will likely not change much over time although dry weight of course does.…”

“…Individual moult events were only tracked for marked shrimps, and although this provides the time span since the last moult, it does not provide information on when the next moult will take place. Since crustaceans exhibit continuous weight growth but incremental (discontinuous) length growth, which is hindered by the hard structure of the exoskeleton (Blaxter and Outhward 1991), DWC can vary according to the moult stage (Perger and Temming 2012). Hence, growth is a steady replacement of water by protein (Rosa and Nunes 2004), and two similar sized shrimps can display different dry weights only because they are in different stages of the moult cycle.…”

Age estimation of brown shrimp Crangon crangon: comparison of two approaches applied to populations at the biogeographic edges

“…This is, for example, reflected in the uncertainty about the species' maximum age, which is considered to vary between 1 and 5 yr (Havinga & Willer 1929, Havinga 1930, Lloyd & Yonge 1947, Tiews 1954, Oh et al 1999). More recently, Perger & Temming (2012) proposed a new method to determine in situ growth rates based on the dry weight condition before and after a moult event. Despite promising to discriminate growing shrimps from the starving ones that will not contribute to population growth, again, this method does not effectively determine the age of shrimps.…”

Comparing the Response of the Brown ShrimpCrangon crangon(Linnaeus, 1758) to Prolonged Deprivation of Food in Two Seasons

“…In turn it preys heavily upon several benthic species such as bivalve spat and juvenile plaice (Pihl & Rosenberg 1984, Van der Veer et al 1991, Ansell & Gibson 1993, Van der Veer et al 1998, Oh et al 2001, Amara & Paul 2003, Campos & Van der Veer 2008. Besides this ecological role, the species is a valuable fishery resource in the North Sea, with annual catches of up to 37.000 t and a peak landing value of more than 100 million Euro (ICES 2009, Perger & Temming 2012; in south Europe it is only subjected to a small scale fishery in the Adriatic Sea.…”

“…As the shrimp mature, they move to water of higher salinity. This out-migration from low salinity water is related to the reproduction season (Siegfried 1989, Perger & Temming 2012.…”