Gadoid Fish Species Research Articles

Specific enzyme detection following isoelectric focusing as a complimentary tool for the differentiation of related Gadoid fish species

The presence of specific enzymes in the sarcoplasmic protein fraction of eight gadoid fish species has been investigated following isoelectric focusing (IEF) in the 3.5–9.5 pH range. Lactate dehydrogenase (LDH) and glycerol-3-phosphate-dehydrogenase (G-3-PD) allowed the differentiation of most of the gadoids tested, even in the case of closely related species belonging to the genus Merluccius. Investigation of arginine kinase and creatine kinase afforded non-specific enzyme patterns in the species tested. Adenylate kinase and malate dehydrogenase did not give specific or reproducible enzyme patterns. Analysis of LDH and G-3-PD activities in commercial IEF gels was shown to be a reliable and reproducible technique for distinguishing closely related Merluccius spp. and other gadoid fish species.

Two-Dimensional Electrophoretic Study of the Water-Soluble Protein Fraction in White Muscle of Gadoid Fish Species

Eight gadoid fishesfive hakes (Merluccius spp.), cod (Gadus morhua), pollack (Pollachius pollachius), and blue whiting (Micromesistius poutassou)were characterized in their water-soluble protein profiles by two-dimensional (2D) electrophoresis both by nondenaturing isoelectric focusing (IEF) in the 4−6.5 pH range and gradient SDS−PAGE in the 12−14% range. Species-specific parvalbumin patterns (MW < 13 kDa, pI < 4.6) were observed in most of the species. 2D analysis of mixed extracts revealed that M. merluccius had one parvalbumin (10.4 kDa, pI 3.9) in common with M. australis and M. hubbsi, and two parvalbumins (10.3 kDa, pI 4.1; 10.4 kDa, pI 3.9) in common with M. capensis, respectively. 2D electrophoresis allowed detailed characterization of both the isoelectric points and molecular weights of the major water-soluble proteins and proved to be a valuable tool for the differential characterization among closely related Merluccius spp. Keywords: Identification; species; 2D electrophoresis; isoelectric focusing; fish; Merluccius spp.; gadoids

Reversed-Phase HPLC as a method for the identification of gadoid fish species

A simple and rapid method to identify raw or frozen gadoid fish species is described. The methodology is based on the HPLC separation of water-soluble proteins and monitoring at 230 nm. Chromatographic profiles were reproducible between individuals belonging to the same species; lower variations in the relative retention time than in peak area percentage were observed. Results obtained from an ANOVA test allowed the distinction of characteristic peaks. Profiles were independent of fish quality: fish refrigerated for 10 days showed the same HPLC protein profile as those that were fresh. The ability of the identification procedure was checked by analysis of a set of frozen commercial samples.

PCR amplification of a polymorphic minisatellite VNTR locus in whiting (Merlangius merlangus L.).

An approach has been developed for the screening of allelic variation of minisatellite DNA loci that substantially reduces the time and hazards involved. Primers were designed for a minisatellite region isolated from a gadoid fish species (Merlangius merlangus L.), enabling amplification by polymerase chain reaction, so that differences in the number of minisatellite repeat units (allelic variability) were detectable by ethidium bromide fluorescence (over UV light) following separation by agarose gel electrophoresis. This amplifiable minisatellite variable number tandem repeat region, the first non-primate marker of its kind can be used successfully with DNA extracted by a rapid Chelex protocol. From a sample of 97 individuals, 24 alleles were resolved (750-2200 kb) and heterozygosity was estimated at 0.94.

Review

Proteins of fish muscle undergo chemical and physical changes during frozen storage which may result in, under certain conditions (i.e. long periods of storage, poor freezing practices, temperature fluctuations, etc), loss of quality, reflected mainly by an unacceptable texture as well as an undesirable flavour, odour and colour. In frozen gadoid fish species, most of these changes are caused by the production of formaldehyde in the muscle. Formaldehyde is produced, along with dimethylamine, by the enzymatic reduction of trimethylamine oxide (TMAO). Many aspects of formaldehyde production by TMAO demethylase (TMAOase) have been studied throughout the last decade. In addition, different approaches have been used to investigate the effect of formaldehyde production on protein denaturation and the associated muscle textural changes. Some insight into the reaction between protein and formaldehyde has clarified the possible mechanism of formaldehyde-mediated denaturation. However, evidence of covalent bonding between proteins and formaldehyde, to form crosslinks, has not explained fully the changes observed in fish proteins during frozen storage. The study of cold-induced denaturation of proteins might give new clues for further investigation of the problem. The implications of formaldehyde in toxicological and nutritional issues is also reviewed, as general concern about the safety of food products is a growing field in food science. Finally, different approaches have been proposed to avoid the detrimental action of formaldehyde during frozen storage of gadoid fish; they are some of the practical applications of the knowledge acquired after years of study of different workers in the field.

The predictive power of empirical relationships describing size selectivity, with application to gadoid fish

The use of empirical linear relationships between 50% retention length ( L 50%) and codend mesh size ( MS) of historical selectivity experiments has been suggested whenever selection data on a particular fish species are not readily available. However, when this procedure has been used in prediction, the predictive power of the fitted regression lines has been largely disregarded. Regression lines with large coefficients of determination (r 2) usually significant at α=0.05 or α=0.10, are considered appropriate, and the estimated regression coefficients are used to predict L 50% values for given mesh sizes without any consideration for prediction errors. We analyzed historical data of 689 selectivity experiments for 12 gadoid fish species and calculated an all-gadoids regression line as L 50%=−0.0831 + 0.344 MS( r 2=0.739). The predictive power of the regression was assessed by means of the ‘one item out’ cross-validation technique, and was found to be low in spite of the relatively high coefficient of determination. We investigated the effects of more homogeneous data sets on r 2 and predictive power by repeating the regression and cross-validation analyses on subsets including the results of selectivity experiments carried out on the same species, with the same experimental method (alternate-haul or covered codend) and codends of similar material. We found that (1) many simple linear models generally have low predictive powers in spite of their relatively large coefficients of determination, which reduces the value of their predictions for assessment or management purposes, and (2) linear regressions based on more homogeneous data subsets often display smaller prediction errors and larger coefficients of determination. Consequently, we suggest that the predictive power of empirical relationships describing size selectivity should be considered to select the regression line that provides more precise estimates of L 50%.

Distribution and trophic ecology of some gadoid fish of the Norwegian deep

Abstract As part of a comprehensive study of fish assemblages of the deep-water area of the northeastern North Sea and Skagerrak called the Norwegian Deep, information was gathered on the ecology and biology of selected gadoid fish species, i.e. saithe (Pollachius virens), cod (Gadus morhua), whiting (Merlangius merlangos), blue whiting (Micromesistius poutassou), pollack (Pollachius pollachius), ling (Molva molva), blue ling (Molva dipterygia), tusk (Brosme brosme) and hake (Merluccius merluccius). Data were collected on trawl surveys in winter, summer and autumn of the years 1984–1987. The distribution, abundance, size and age composition and diet of each species were described and intraspecific differences in diet and distribution were considered. The entire Norwegian Deep, but particularly the western and southern slopes, serves as feeding area for all the nine gadoids considered and most of the species utilize the area as late juveniles and adults, some also as young juveniles. Blue whiting and saith...

The ultrastructural organization of olfactory epithelium of two species of gadoid fish

The untrastructural organization of the olfactory epithelium of the cod Gadus morhua (L.) and the haddock Melanogrammus aeglefinus (L.) was studied using both transmission and scanning electron microscopy. The olfactory rosette was found to exhibit regional differences; the faces of the olfactory lamella were composed of sensory epithelium, the edges were non‐sensory. The cellular organization of the olfactory epithelium was determined and consisted of bi‐polar sensory neurones, supporting cells, mucous cells and basal cells. The ultrastructure of the sensory cells was consistent, having an elongate cell, the free surface of which terminated in an olfactory vesicle from which arose either four olfactory cilia or numerous microvilli. Ciliary aggregations have been found in the two species of gadoid fish studied; it is suggested that these structures aid in the separation and in the circulation of fluid between the lamellae. The surface structure of the supporting cells was found to be of two types: either ciliated or ridged; the former presenting distinct ciliated tufts, the latter showing definite, but unorganized, ridges over the epithelium surface.

The occurrence of ciliary aggregations on the olfactory epithelium of two species of gadoid fish

Ciliary aggregations have been found to occur on the olfactory epithelium of Gadus morhua (L.) and Melanogrammus aeglefinus (L.). The fine structure of ciliary aggregations is constant, consisting of 9 +2 complexes enclosed by a single membrane, though the number of complexes may vary within any ciliary aggregation. It is suggested that ciliary aggregations are motile structures associated with the sensory epithelium and may assist in the circulation of fluid between lamellae.

Production of Dimethylamine in Muscle of Several Species of Gadoid Fish during Frozen Storage, Especially in Relation to Presence of Dark Muscle

During frozen storage at −5 C, dimethylamine (DMA) was produced in the muscle of five gadoid species. The amount was lowest in haddock and increasingly higher in cod, pollock, cusk, and hake. When the dark lateral muscle was removed from the fillets before freezing, formation of DMA during frozen storage was either inhibited or greatly reduced. Under the same storage conditions no DMA was produced in the muscle of halibut, plaice, redfish, or wolffish.