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Annual, seasonal and spatial differences in the growth rate of Baltic cod larvae and early juveniles in relation to zooplankton biomass fluctuations in 2006-2014

Spich Katarzyna, Fey Dariusz Piotr

Oceanological and Hydrobiological Studies

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2023

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Vol. 52, No. 4

399--419

EN

It is an acknowledged theory that a faster growth rate, determined by various environmental drivers, may boost the survival of larval and juvenile fish. In this study we examined the differences in the growth rate of larval and juvenile cod (age 2 – 136 d; SL: 4.1 – 39.2 mm) between the years 2006 and 2014, sub-areas of the Baltic Sea (Bornholm Basin, BB; Słupsk Furrow, SF; Gdansk Basin, GB), and seasons (spring and summer). The average growth rate for all specimens was 0.25 mm/d, with significantly lower values between 2012 and 2014 than between 2006 and 2011. A reduction in zooplankton biomass, especially the large zooplankton fraction, was observed after the 2006–2008 period, which was related to the prevailing temperature conditions in the surface layers. The reduction in zooplankton biomass was accompanied by changes in the structure of zooplankton: less T. longicornis, C. hamatus, and Pseudocalanus spp., and more Acartia spp. The results suggest that the inter-annual differences observed in zooplankton biomass and structure are likely responsible for the observed reduction in the growth rate of cod larvae between 2012 and 2014 compared to the years between 2006 and 2011. The growth rate reduction could be one of the reasons for the decline in the recruitment of eastern Baltic cod between the years 2013 and 2015, after the high recruitment years of the period 2011-2012.

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Distribution of anisakid nematodes in the muscle tissue of cod (Gadus morhua) from the Norwegian Sea

Nadolna-Ałtyn Katarzyna, Podolska Magdalena Maria, Pawlak Joanna, Szostakowska Beata

Oceanologia

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2022

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No. 64 (3)

489--502

EN

Atlantic cod (Gadus morhua) is an important commercial fish species on the world market. The aim of our studies was to explore the presence, intensity of infection and distribution of the zoonotic nematodes of the different genera of Anisakidae in the muscle tissue of G. morhua from the Norwegian Sea. Cod from fishing areas FAO IIa1 (n = 50) and FAO IIa2 (n = 56) were sampled in March 2017. The unskinned flesh of each fish was examined using a white-light transilluminator. Collected parasites were identified to the genus level, and a subsample was identified using molecular methods. We found a higher prevalence of infection with Anisakis than with Pseudoterranova in the musculature of cod from both fishing areas. In FAO IIa1, a lower prevalence of infection with Pseudoterranova was recorded (14%) than in FAO IIa2 (∼39%). However, the intensity of infection was higher (53) in FAO IIa2 than in FAO IIa1 (8 parasites per fish). The opposite was found with Anisakis (prevalence 88% in FAO IIa1 and ∼55% in FAO IIa2, intensity up to 30 and up to 25 parasites per fish respectively). Most Anisakis larvae were present in the belly flaps (predominantly the left side), while Pseudoterranova spp. were dispersed with descending frequency in belly flaps, dorsal fillet and caudal fillet. Molecular identification revealed the presence of A. simplex (s.s.), P. decipiens (s.s.) and P. krabbei in both areas, and a hybrid of P. decipiens and P. krabbei in FAO IIa2.

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First record of brown colouration of Atlantic cod (Gadus morhua, L.) from the North Sea [commun.]

Rybczyk A., Czerniejewski P., Rokicka-Praxmajer J.

Oceanologia

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2014

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No. 56 (1)

159--163

EN

This paper reports the biological characterisation of a specimen of Atlantic cod (Gadus morhua L.) with a unique brown colour, which is the first fish of this species with such a colouration recorded from European waters. It was caught in the coastal zone of the North Sea in June 2011. This "brown" cod fish weighed 1074.3 g and had an overall length of 422 mm.