Marking otoliths of Baltic cod (Gadus morhuaLinnaeus, 1758) with tetracycline and strontium chloride

Abstract

Summary Identified were suitable dosages of tetracycline hydrochloride (TET) in three single treatments and three combined treatments of TET with 2 mg/kg strontium chloride (STR) in wild western Baltic cod (Gadus morhua), in terms of (a) obtainable mark qualities (visibility of fluorescent bands), (b) growth assessment, and (c) induced mortality rates. Isotonic NaCl solution was injected in a control group (25 cod per treatment). The results provide the basis for imperative age validation studies of Baltic Sea cod. Cod originating from pound nets near Fehmarn Island were kept in swimming net cages at the harbor of Warnemünde for 1.5 months. Mean initial total length was 28(±3) cm (salinity: 13, water temperature: 13 to 8°C). Overall average growth of surviving cod was 0.8 mm/day. In single TET treatments, lowest mortality rates and best mark quality were observed for TET concentrations of 100 compared to 50 and 25 mg/kg wet mass. Mortality rates of the 100 mg/kg treatment group were remarkably lower than in the control group emphasizing the antibiotic effect of TET. By contrast, the double treatment in the TET‐STR groups resulted in a binding interaction between both markers in the fish body causing either the antibiotic potency being inhibited or TET and STR forming a non‐beneficial chelate (increased mortality), and decreased incorporation of TET in the otolith (reduced visibility of TET bands). Consequently, TET (short‐term marker) and STR (long‐term marker) should not be injected together. Our results demonstrate that the binding interactions between these substances known from homoiotherm animals also apply for poikilotherms such as fish.

Multidecadal changes in fish growth rates estimated from tagging data: A case study from the Eastern Baltic cod (Gadus morhua, Gadidae)

“…In addition, Stötera et al. (2018) found no significant effect of injection with tetracycline (that was used in the two most recent tagging periods, 2003–2006 and 2016–2019) on short‐term growth of Baltic cod. Another factor that could affect growth estimates is the selectivity of the recapture gears, with passive gears and recreational angling with rod and line being selective for boldness (Arlinghaus et al., 2017).…”

“…Fish in good health were tagged externally using numbered T‐bar anchor tags inserted across the pterygiophores below the first dorsal fin and internally through intraperitoneal injection of tetracycline‐hydrochloride (following Stötera et al., 2018). In addition, a subset (5%) of cod was tagged with surgically implanted DSTs and marked externally with two T‐bar anchor tags.…”

Regional and stock-specific differences in contemporary growth of Baltic cod revealed through tag-recapture data

“…A subset of cod for the TABACOD project were also surgically implanted with data storage tags (Table 1). It was assumed that tagging type did not influence the fish growth rate, an assumption that is partially justified by previous experiments (Righton et al, 2006;Stötera et al, 2018).…”

Evaluation of the Effectiveness of Marking Juvenile Takifugu obscurus Otoliths with Strontium

“…Otolith fluorescent marks [18], stable isotope otolith fingerprint marks [19], strontium marks in otolith [20], and otolith thermal marks [18] are more broadly used. Strontium mark in otolith, as a new method, has been widely applied in various teleost fish, such as Gadus callarias [21], Oncorhynchus keta [22], Acipenser fulvescens [23], and Anguilla anguilla [24]. Because otoliths are metabolically inert, it is difficult to change the fingerprints for the element once it is deposited.…”