Seasonal variability of gillnet selectivity in Chilean hake Merluccius gayi gayi (Guichenot, 1848)

This study examines the seasonal variability in gillnet size selectivity for the main Chilean hake (Merluccius gayi gayi) fishery off the coast of central Chile. Selectivity estimates were based on five gillnet mesh sizes (50, 60, 70, 80, 90 mm) in four traditional fishing areas, and during periods of low and high reproductive activity. Average fish length caught in the earlier period (low reproductive activity) was 30.8 cm LT (±4.17), and significantly longer (p < .05) at 35.9 cm TL (±6.15) in the latter period (high reproductive activity). For males, the selectivity factor was similar in both periods, thus the estimated modal lengths did not differ seasonally (p > .05). For females, however, both the selectivity factor and the estimated modal lengths changed significantly depending on the time of year (p < .05). A significant increment was estimated in the girth/perimeter ratio and condition factor during the period of higher reproductive activity. This change in the fish girth of females during spawning helps explain the significant reduction in their selectivity factor estimates in August–October.     

Genetic differentiation in Chilean hake Merluccius gayi gayi (Pisces: Merlucciidae)

The genetic structure of Chilean hake Merluccius gayi gayi, was analyzed using starch gel protein electrophoresis. Samples were collected from four localities along the coast off Chile. A total of 1500 specimens sampled from Coquimbo, San Antonio, Talcahuano and Puerto Montt were used in the study. Genetic information was obtained for six allozyme loci Pgi-1, Pgi-2, Pgm, Idh-1, Idh-2 and Aat. The results of the analysis showed no significant allelic differences among samples from various localities, with an average F_ST value of 0.007 for all loci and samples. A heterogeneity test for all loci and specimens from the four localities showed only two significant values. Thus, Chilean hake populations along the coast of Chile appear to be genetically homogeneous.     

Larval anisakids and other helminths in the hake, Merluccius gayi (Guichenot) from Chile

One hundred and twenty hake Merluccius gayi caught off central Chile were examined for helminth parasites. Sixty hake were kept in ice from the catch of a trawler were examined upon arrival at port, while the other 60 hake were dissected on board immediately after collection. Ninety one per cent of hake were infected with one or more species of the following helminths: trypanorhynch plerocerci of Grillotia dollfusi Carvajal, 1971; adult worms of the genus Clestobothrium; larval nematodes of the genera Anisakis and Phocanema; 86% of the total were infected with Anisakis sp. and 42.5% with Phocanema sp. Infection with larval nematodes increased with length of the fish and there was a greater incidence of infection among the females. There was a greater frequency of occurrence of the parasites in the viscera than in the musculature.     

A study of the migration of larval Anisakis simplex (Nematoda: Ascaridida) in the Chilean hake, Merluccius gayi (Guichenot)

Hake were collected during four trips to investigate a possible migration from viscera to somatic musculature of larval Anisakis simplex. On each trip 150 hake were examined and separated in five groups of 30 hake. One group consisted of fish gutted immediately after capture; two other groups were gutted 15 h after capture, one of which had been left at environmental temperature, and the other put in ice; the remaining two groups (exposed to the same treatment) were gutted 30 h after capture. All fish flesh was digested (HCl-pepsin digest); all nematodes found in the digest and in the viscera were counted. There was no increase of larval nematodes in flesh at 15 and 30 h. Temperature did not affect the migration of larvae. A regression test did not show significant differences between groups. Finally, there was no correlation between number of larvae in viscera and in musculature.     

Population structure in Chilean hake Merluccius gayi as revealed by mitochondrial DNA sequences

Genetic variation and divergence among samples of Chilean hake Merluccius gayi, from three localities off the coast of Chile and one locality off the coast of northern Peru, were assessed using sequences from the control region of mitochondrial DNA. Homogeneity tests revealed occurrence of at least three distinct genetic stocks of M. gayi within the region sampled. Factors potentially contributing to genetic divergence among M. gayi probably include hydrodynamics and behaviour.     

Trypanosoma humboldti n. sp. from the Chilean catshark, Schroederichthys chilensis (Guichenot, 1848)

The morphology of Trypanosoma humboldti n. sp. is described from living and stained specimens obtained from the blood of a catshark, Schroederichthys chilensis. This represents the first report of a trypanosome in fish from the eastern Pacific Ocean. It is distinguished by its size and apparent lack of pleomorphism. The presence of a leech, Branchellion ravenellii, attached to the catshark, raises the possibility that it can act as a vector. Additionally, this leech is recorded for the first time from the Pacific Ocean.     

Trypanosoma humboldti n. sp. from the Chilean Catshark,Schroederichthys chilensis (Guichenot, 1848)1

The morphology of Trypanosoma humboldti n. sp. is described from living and stained specimens obtained from the blood of a catshark, Schroederichthys chilensis. This represents the first report of a trypanosome in fish from the eastern Pacific Ocean. It is distinguished by its size and apparent lack of pleomorphism. The presence of a leech, Branchellion ravenellii, attached to the catshark, raises the possibility that it can act as a vector. Additionally, this leech is recorded for the first time from the Pacific Ocean.     

Populations and assemblages of parasites in hake, Merluccius gayi, from the southeastern Pacific Ocean: stock implications

To assess fish stocks, the populations and community assemblages of metazoan parasites were compared in 1172 Chilean hake Merluccius gayi landed at two major ports, and caught during 1991–1992 in three major fishing areas off central Chile. At least two ecological stocks are suggested, based on consistent differences in parasitism between body length classes for Grillotia dollfusi, Hysterothylacium sp., Clestobothrium crassiceps and Aporocotyle wilhelmi . More use should be made of the information on whole parasite assemblages including, for example, patterns of co-occurrence of parasite species. Univariate analyses on selected taxa in samples from different areas may show no differences because of the same prevalence or abundance for each parasite taxon, but opposite numerical arrangements of co-occurring taxa in community assemblages would remain undetected.     

Size selectivity of three diamond mesh codends for the European hake (Merluccius merluccius) and the tub gurnard (Trigla lucerna) in the Sea of Marmara, Turkey

The effects of an increase in the codend mesh size from 44 to 56 and 80 mm on size selectivity of the two by‐catch species (the European hake Merluccius merlucius and the tub gurnard Trigla lucerna) commonly captured in the shrimp fishery in the Sea of Marmara, were evaluated. The parameters of the logistic selectivity model were estimated by maximum likelihood. Length at 50% retention, L₅₀, was found to increase with mesh size for both species. The L₅₀ values of 44, 56 and 80 mm were, respectively, 19.8, 21.5 and 33.4 cm for European hake, 17.9, 17.7 and 25.6 cm for tub gurnard. The main conclusions are that 44 mm and 56 mm diamond mesh codends retain a considerable amount of undersized hake and tub gurnard as by‐catch in the shrimp fishery. With 80 mm mesh size codend, most juvenile European hake are released. For the tub gurnard, however, even this mesh size does not provide a good enough selection. From the biological point of view, it is concluded that the legal 44 mm diamond mesh codend does not provide satisfactory selection for European hake and the tub‐gurnard in trawl fisheries of the Sea of Marmara.     

Genetic structure and environmental heterogeneity in the European hake (Merluccius merluccius)

This study aimed at assessing the genetic structure and the state of the stocks of the European hake (Merluccius merluccius). To this end, 15 samples were taken from the whole range of the species and analysed using allozymes. Since 11 samples were taken from the poorly studied Mediterranean Sea, the results obtained provided a complete picture of the hake's genetic structure and an initial insight into its relationships with environmental features. Atlantic and Mediterranean hake populations are separated by the Almeria-Oran front. This area has been proved to be the boundary between Atlantic and Mediterranean stocks of many marine organisms, but some doubt exists concerning the efficaciousness of the local gyres as barriers to the gene flow. Our data have evidenced a latitudinal cline at loci Gapdh and Gpi-2 within the Mediterranean Sea, with a further steep change across the Almeria-Oran front. The genetic pattern showed a strong correlation with the values of the salinity both at the surface and at -320 m and of the salinity + temperature at the surface, suggesting a role for these parameters in maintaining the genetic differentiation among the two population groups through selective processes. Finally, the levels of genetic variability were found to be slightly lower in the depleted Atlantic stock than in the Mediterranean one.     

Acid phosphatase activity in pre- and post-spawning hake (Merluccius hubbsi)

1. The specific activity of muscle acid phosphatase (E.C. 3.1.3.1.) in pre- and post-spawning hake was investigated. 2. Specific activity values, 0.54 in pre-spawning hakes and 1.64 in post-spawning fish, have been obtained. 3. Using a histochemical test, acid phosphatase has been localized mainly in the connective tissue. The strongest reaction has been observed in post-spawning hake. 4. The increase of the lysosomal activity in the connective tissue may be related to the changes found in the muscle texture associated with spawning.     

Diet of two large sympatric teleosts, the ling (Genypterus blacodes) and hake (Merluccius australis)

Ling and hake are tertiary consumers, and as a result both may have an important structuring role in marine communities. The diets of 2064 ling and 913 hake from Chatham Rise, New Zealand, were determined from examination of stomach contents. Ling was a benthic generalist, and hake a demersal piscivore. The diet of ling was characterised by benthic crustaceans, mainly Munida gracilis and Metanephrops challengeri, and demersal fishes, mainly Macrourids and scavenged offal from fishing vessels. The diet of hake was characterised by teleost fishes, mainly macrourids and merlucciids. Multivariate analyses using distance-based linear models found the most important predictors of diet variability were depth, fish length, and vessel type (whether the sample was collected from a commercial or research vessel) for ling, and fish length and vessel type for hake. There was no interspecific predation between ling and hake, and resource competition was largely restricted to macrourid prey, although the dominant macrourid species predated by ling and hake were different. Cluster analysis of average diet of intraspecific groups of ling and hake confirmed the persistent diet separation. Although size is a central factor in determining ecological processes, similar sized ling and hake had distinctly different foraging ecology, and therefore could influence the ecosystem in different ways, and be unequally affected by ecosystem fluctuations.     

Genetic tags applied to the European hake, Merluccius merluccius (L.)

Three biochemical gene markers test the hypothesis that the European hake, Merluccius merluccius (L.), along the west European continental shelf are one race. The three polymorphic loci were serum transferrin (Tf), eye vitreous fluid butyric esterase (Es) and liver superoxide dismutase (Sod). Five transferrin alleles, three esterase alleles and two superoxide dismutase alleles were identified. Heterogeneity tests on genotype frequency distribution for twelve areas ranging from Norway to Biscay revealed no significant variation. The results using these genetic tags are consistent with the unit race hypothesis for hake throughout the sea areas sampled.     

Genetic tags applied to the European hake, Merluccius merluccius (L.)

Three biochemical gene markers test the hypothesis that the European hake, Merluccius merluccius (L.), along the west European continental shelf are one race. The three polymorphic loci were serum transferrin (Tf), eye vitreous fluid butyric esterase (Es) and liver superoxide dismutase (Sod). Five transferrin alleles, three esterase alleles and two superoxide dismutase alleles were identified. Heterogeneity tests on genotype frequency distribution for twelve areas ranging from Norway to Biscay revealed no significant variation. The results using these genetic tags are consistent with the unit race hypothesis for hake throughout the sea areas sampled.     

Exploitation and mortality rates of European hake (Merluccius merluccius) in the Aegean Sea (Izmir Bay,Turkey)

Experimental trawl surveys in Izmir Bay (Aegean Sea) were taken seasonally between 2007 and 2009. A total of 1353 specimens were sampled ranging from 5.9 cm (1.4 g) to 44.4 cm (670 g). The main size group of Merluccius merluccius was between 14 and 25 cm total length (TL). In total, the mean catch per unit effort (CPUE) for hake by number and weight was 101.4 ± 18.4 ind h^?1 and 10.7 ± 1.5 kg h^?1, respectively. Highest mean CPUE by number and biomass was determined as 257.1 ± 15.1 ind h^?1 and 15.1 ± 4.9 kg h^?1 in summer. Mortality (M, F, Z) ratios of hake were 0.58 year^?1, 1.66 year^?1 and 2.24 year^?1, respectively. Because of the many smaller specimens caught in this study, this seems to indicate that there may be heavy fishing pressures on the hake population; the high exploitation rate (E = 0.74) appears to confirm this conclusion.     

SSU rDNA analysis of Kudoa rosenbuschi (Myxosporea) from the Argentinean hake Merluccius hubbsi

The cloning and sequencing of the small subunit (SSU) ribosomal DNA gene from Kudoa rosenbuschi (myxosporean species associated with post-mortem myoliquefaction process in the Argentinean hake Merluccius hubbsi) is reported. The SSU rDNA was found to contain 1740 bp with a single polymorphic site with either a C or T at position 221. The sequence data obtained in this study and those known sequences of Kudoa species deposited in the GenBank were all analyzed to construct a phylogenetic tree. Nucleotide sequences showed the highest degree of identity with K. funduli, followed by K. miniauriculata, K. clupeidae and K. dianae. Phylogenetic analysis placed K. rosenbuschi in the same branch of K. clupeidae and K. funduli, and showed it to be closely related to K. dianae, K. paniformis and K. miniauriculata.     

Esterase polymorphism in vitreous fluid of Pacific hake, Merluccius productus

Three regions of esterase activity designated I, II, and III were found on zymograms of vitreous fluids. Region I, the most anodal, exhibited two zones, one of which (the slower) was in all samples, occasionally accompanied by a second band which moved just ahead of it. Likewise, Region III, the most cathodal, exhibited two phenotypes, a common one-band and a rare two-band phenotype. Region II was occupied by one- and two-banded combinations of five different zones (a, b, c, d and e), which indicated that each band was the product of an allelic series of genes (EsII ^a, EsII ^b, etc.).
Only 11 of 15 expected phenotypes were encountered because of the rarity of alleles EsII ^a and EsII ^c. The most common allele, EsII ^b, had a frequency of 0.83 in Puget Sound hake and 0.60 in Pacific Ocean hake; this difference was highly significant. In the Pacific Ocean population agreement was good between observed and expected numbers, assuming Hardy-Weinberg equilibrium. In the Puget Sound samples deviations from expected frequencies did not appear in females or first-year fish, but deviations were significant in males 2 years and older; these deviations occurred as a marked deficiency of bd males combined with an excess of bb and dd males, particularly the latter. Inhibition tests indicated that these isozymes are B esterases. Estimations of molecular weight for the isozymes of Region II based on chromatographic and ultracentrifugation methods were 70,000 and 73,500, respectively.     

Development of the digestive system of Argentine hake,Merluccius hubbsi,larvae

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.