Comparative gonad histology and semen quality of normal (XY) and neo‐males (XX) of Atlantic salmon (Salmo salar)

With an overarching objective of improving the hatchery production of Atlantic salmon (Salmo salar) all‐female progeny, this study comparatively evaluated the reproductive parameters between normal (genotype XY) and neo‐males (genotype XX). Four normal (XY) and seven neo‐ (XX) males, from the same brood stock, distinguished by their ability to or lack of expressing semen, respectively, were comparatively evaluated. The left testicular lobe was used for histomorphometric analyses, while the right for semen collection and sperm quality analyses. Histomorphometric observations revealed that neo‐male testes are irregularly shaped, and have poorly formed seminiferous ducts, higher proportions of interstitial tissue and lower gonadosomatic index (p < .05). In addition, hypertrophied and cyst forming Sertoli cells were found in these individuals which collectively appear to form a physical barrier, precluding the semen collection by standard stripping techniques and reducing sperm quality. Particularly, semen motility (80.69 ± 2.4% and 57.2 ± 36.5% for XY and XX respectively) and duration of motility (99.31 ± 28.03 s and 66.84 ± 23.83 s for XY and XX respectively) of neo‐males were most compromised (p < .05). Interestingly, the TUNEL assay indicated no signs of apoptotic tissue suggesting that the histological differences may relate to delayed physiological/sexual maturity of neo‐males.     

How are the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) in Atlantic salmon farming affected by different control efforts: A case study of an intensive production area with coordinated production cycles and changing delousing practices in 2013–2018

The aims of the present study were to describe the salmon lice (Lepeophtheirus salmonis Krøyer, 1837) situation in an intensive salmon production area in mid‐Norway and to consider implications of changing practices of how salmon lice infestation can be controlled. The results in this study suggest that there are steps that can be carried out to keep salmon lice under control even during years when the temperature facilitates a quick salmon lice development. The present work indicates that the use of cleaner fish can delay the time it takes adult female lice to reach 0.1 per salmon in the beginning of a production cycle. It suggests that the timing of cleaner fish deployment into salmon cages can influence its effectiveness in controlling salmon lice. It also gives caution to letting salmon lice develop unchecked, even at levels far below the current lice limit, because of the difficulties to control salmon lice when the external infection pressure is too high. This study took place during a rapid change in delousing methods, in an area with coordinated salmon production. Despite its exploratory nature, this study offers insights into the salmon lice fluctuations in relation to efforts aimed at controlling it.     

Effects of embryonic exposure to α‐lipoic acid or ascorbic acid on hatching rate and development of zebrafish (Danio rerio)

This study investigates the effects of embryonic exposure to two different antioxidants on growth and development in fish. Zebrafish (Danio rerio) embryos (100 per group) were exposed to lipoic acid (LA, 6–12 μM) or ascorbic acid (AA, 100–200 μM) and the hatching rate, standard lengths (SL) at hatching, development and growth post‐hatching monitored. The SLs at hatching were increased (P<0.05) in both antioxidant‐exposed groups relative to the controls, with no effect on yolk reserves. This enhanced development persisted up to 15 days post hatching. At hatching, cell proliferation rates (P<0.0005) and basic fibroblast growth factor (P<0.001), were greater in the antioxidant‐exposed fish than in the controls (0 μM antioxidant); no oxidative DNA damage was detected (P>0.05). Activity of the endogenous antioxidant enzyme superoxide dismutase was greater (P<0.001) in LA‐treated fish than in the controls. The results suggest that embryonic treatment of zebrafish with LA or AA during embryogenesis enhanced cell proliferation, leading to increased somatic growth in the larval stages, persisting into the juvenile stage. The findings support the treatment of embryonic fish with antioxidants for enhanced results in aquaculture.     

Long‐term records (1781–2013) of European eel (Anguilla anguilla L.) production in the Comacchio Lagoon (Italy): evaluation of local and global factors as causes of the population collapse

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牙鲆和半滑舌鳎5S rDNA基因的染色体定位及鲽形目5种鱼类的分子系统学分析

利用荧光原位杂交(FISH)技术将5S rDNA基因定位在牙鲆和半滑舌鳎染色体上,结果表明,5S rDNA基因在雌、雄性半滑舌鳎的一对同源染色体上分别存在2个杂交信号位点;在二、三倍体牙鲆的同源染色体上分别存在2个和3个杂交信号位点,杂交信号明显且特异。本研究首次将5S rDNA基因定位在半滑舌鳎和三倍体牙鲆的染色体上,为牙鲆及半滑舌鳎倍性鉴定、染色体鉴别提供了有效方法。此外,根据牙鲆5S rDNA基因编码区序列设计引物,扩增出大菱鲆和半滑舌鳎5S rDNA基因编码区序列,与鲽、塞内加尔鳎、大口黑鲈、七鳃鳗的5SrDNA基因序列进行同源性比较后发现,5种鲽形目鱼类5S rDNA基因序列同源性高达98.3%,系统发生分析结果显示5种鲽形目鱼类聚为一支;各序列中GC含量均显著高于AT含量。     

Phenotype of Aeromonas salmonicida sp. salmonicida cyclic adenosine 3′,5′‐monophosphate receptor protein (Crp) mutants and its virulence in rainbow trout (Oncorhynchus mykiss)

Precise deletion of genes related to virulence can be used as a strategy to produce attenuated bacterial vaccines. Here, we study the deletion of the cyclic‐3′,5′‐adenosine monophosphate (cAMP) receptor protein (Crp) in Aeromonas salmonicida, the aetiologic agent of furunculosis in marine and freshwater fish. The Crp protein is a conserved global regulator, controlling physiology processes, like sugar utilization. Deletion of the crp gene has been utilized in live attenuated vaccines for mammals, birds and warm water fish. Here, we characterized the crp gene and reported the effect of a crp deletion in A. salmonicida virulent and non‐virulent isolates. We found that A. salmonicida Δcrp was not able to utilize maltose and other sugars, and its generation time was similar to the wild type. A. salmonicida ?crp showed a higher ability of cell invasion compared to the wild type. Fish challenges showed that A. salmonicida ?crp is ~6 times attenuated in Oncorhynchus mykiss and conferred protective immunity against the intraperitoneal challenge with A. salmonicida wild type. We concluded that deletion of A. salmonicida crp influences sugar utilization, cell invasion and virulence. Deletion of crp in A. salmonicida could be considered as part of an effective strategy to develop immersion live attenuated vaccines against furunculosis.     

Change in nutrient composition of Artemia grown for 3–4 days and effects of feeding on‐grown Artemia on performance of Atlantic halibut (Hippoglossus hippoglossus,L.) larvae

Major challenges in culture of Atlantic halibut larvae have been slow growth during the late larval stages and inferior juvenile quality due to pigmentation errors and incomplete eye migration during metamorphosis. The hypothesis of this study was that feeding on‐grown Artemia would alleviate these problems. Artemia were grown for 3–4 days on Origreen or Origo. The growth and nutrient composition of Artemia nauplii and on‐grown Artemia were analysed, and both Artemia types were fed to Atlantic halibut larvae, on‐grown Artemia from 15 days post‐first feeding (dpff). The body length of Artemia increased with 20%–70% in response to on‐growing. In all experiments, protein, free amino acids and the ratio of phospholipid to total lipid increased, while lipid and glycogen decreased. The fatty acid composition improved in some cases and not in others. The micronutrient profiles were not negatively affected in on‐grown Artemia. All these changes are thought to be beneficial for marine fish larvae. The final weight of Atlantic halibut postlarvae was similar, and 90% of the juveniles had complete eye migration in both groups. It is concluded that the present version of Artemia nauplii probably covers the nutrient requirements of Atlantic halibut larvae.     

Protein‐sparing capability of dietary lipid in herbivorous and omnivorous freshwater finfish: a comparative case study on grass carp (Ctenopharyngodon idella) and tilapia (Oreochromis niloticus × O. aureus)

Two, 8‐week feeding trials were conducted to compare protein‐sparing capability of dietary lipid in herbivorous grass carp (Ctenopharyngodon idella) and omnivorous tilapia (Oreochomis niloticus × O. aureus). Utilizing a 2 × 3 factorial design, experimental diets containing two levels of crude protein (380 and 250 g kg⁻¹) and three levels of lipid (0, 40 and 100 g kg⁻¹) were formulated for use in both feeding trials. Growth performances showed better response of both fish fed 380 g kg⁻¹ protein diet than those fed 250 g kg⁻¹ protein diet. Despite the dietary protein level, weight gain (WG), specific growth ratio (SGR), feed conversion ratio (FCR) and protein efficiency ratio were much higher (P < 0.05) for grass carp fed 40 g kg⁻¹ lipid diet than those fed 100 g kg⁻¹ lipid diet; however, there were no significant differences in tilapia fed the two diets. The feed intake of grass carp fed lipid‐free diet was the lowest, but it tended to decrease with increase in dietary lipids in tilapia. Lipid retention (LR) was negatively correlated with dietary lipid concentration of both fish. Viscerosomatic index (VSI), hepatosomatic index (HSI), intraperitoneal fat ratio (IPF) and whole‐body and liver lipid content positively correlated with dietary lipid concentration of both fish. Plasma parameters and liver enzymes activities were also positively correlated with dietary lipid concentration of both fish. Liver lipid contents were higher and enzymes activities were lower in grass carp when compared with tilapia. These data suggested that there was no evidence of a protein‐sparing effect of dietary lipids in grass carp. Tilapia has relatively higher capacity to endure high dietary lipid level compared to grass carp.     

A survey of the distribution of the PKD‐parasite Tetracapsuloides bryosalmonae (Cnidaria: Myxozoa: Malacosporea) in salmonids in Norwegian rivers – additional information gleaned from formerly collected fish

The malacosporean Tetracapsuloides bryosalmonae was detected in kidneys from Atlantic salmon parr in 64 of 91 sampled Norwegian rivers. Using real‐time PCR, this parasite was found to be present in Atlantic salmon parr in rivers along the whole coast, from the northernmost and southernmost areas of the country. In addition, T. bryosalmonae was found in kidneys from brown trout parr in 17 of 19 sampled rivers in south‐east Norway, and in Arctic charr sampled in the River Risfjordelva, located at the northernmost edge of the European mainland. In conclusion, T. bryosalmonae has a widespread distribution in salmonids in Norwegian watercourses. Proliferative kidney disease (PKD) caused by T. bryosalmonae and PKD‐induced mortality has been observed in salmonids in several Norwegian rivers and it can be speculated that more PKD outbreaks will occur as a result of climate change.     

Observation on the spawning of Sardina and Sardinella off the south Moroccan Atlantic coast (21–26°N)

This paper provides information on the early life stages of the Moroccan Atlantic sardine, Sardina pilchardus, and two species of Sardinella: Sardinella aurita and S. maderensis, between Cape Blanc (21°N) and Cape Boujdor (26°N), dealing with the spawning grounds, the nursery areas and the optimal spawning temperature and salinity range.

The spawning areas for Sardina are located North of Dakhla (24°30′–25°30′N) and near Cintra Bay (23°N). The larval development area is described together with seasonal and annual characteristics. The nurseries of Sardina are near Dakhla and to the south between 21 and 22°N but precise locations vary with season. The maximum occurrence of eggs was during winter, and was at temperatures from 16 to 18 °C in winter and between 18 and 18.5 °C in summer.

The main spawning area of Sardinella species is between Cape Blanc and Cintra Bay (21–23°N) with a maximum occurrence of eggs and larvae in July. For Sardinella off the southern region of Morocco, the optimal temperature interval for spawning is between 18 and 21.14 °C. No conclusions can be drawn on the relationship between spawning and water salinity.

The area north of Cintra Bay has a broad, but shallow continental shelf. This topography leads to decreasing dispersion effects and the zone constitutes a favorable area for larval retention and development.     

Movement patterns of adult peacock bass Cichla temensis between tributaries of the middle Negro River basin (Amazonas – Brazil): an otolith geochemical analysis

Geological heterogeneity in the Negro River basin creates differences in isotopic and elemental composition of rivers. Recent studies indicate that ⁸⁷Sr/⁸⁶Sr, Sr/Ca and Ba/Ca can be used to determine the natal origins of peacock bass Cichla temensis (Humboldt) and reconstruct individual movement histories. This method was used to analyse otoliths from adult C. temensis collected from two locations on the mainstem Negro River and six tributaries around these core areas. Applying discriminant functions derived from young‐of‐year reference otolith data to determine natal origins of adults indicated that 42% of adults sampled were collected from the same area in which they were spawned. However, variation in ⁸⁷Sr/⁸⁶Sr isotope values along the axis of otoliths indicated that C. temensis movements are much more dynamic than previously concluded. This new information on the spatial distribution of C. temensis can be used to support effective strategies for fishery management in the Negro River basin.     

The olive oil by‐product in ‘rainbow trout Onchorynchus mykyss (Walbaum)’ farming: productive results and quality of the product

The aim of this work is to investigate olive oil by‐product [vegetation water (VW)] inclusion in rainbow trout diet and its effect on the productive traits and the quality of the product. Two levels of VW inclusion were used and one control group was included. Fish diets were isonitrogeonous (crude protein 40%) and isoenergetic (18 MJ kg^?1 DM). Two thousand and four hundred rainbow trout were used. An in vivo digestibility experiment was performed in order to determine diets’ digestibility. All the fish diets and fillets were analysed to determine the proximate and fatty acid composition. On final fish fillet, lipid oxidation was determined at 0, 24, 48, 72, 96 and 192 h of storage using the 2‐thiobarbituric acid method (thiobarbituric acid reactive substances). Aroma analyses on the final cooked and raw fillet were performed using an electronic nose. The VW inclusion partially reduced protein digestibility. The fish growth varied between 1.08% and 1.1% day. The supplemental level of VW led to a better antioxidant status of fish fillet, in particular, in the fillet sample after 72 h of fillet conservation. Principal component analysis in raw and cooked fish fillet indicates that the VW inclusion in the fish diet led to aroma modification on fish fillet.     

Total egg harvest by the calanoid copepod Acartia tonsa (Dana) in intensive culture – effects of high stocking densities on daily egg harvest and egg quality

Understanding the factors limiting copepod productivity in dense cultures is a prerequisite for the partial or entire replacement of Artemia and rotifers as live feed for finfish larvae. In dense cultures, high encounter rates between individuals may increase stress, cannibalism incidents and potentially trigger resting egg production. We conducted an experiment to evaluate the potential egg production and egg quality of Acartia tonsa stocked at densities ranging from 10 to >5000 ind. L^?1. Egg Production (EP), Delayed Hatching Eggs production (DHE), hatching success (HS), egg mortality and water quality were used as end points. In the present system, A. tonsa was raised at >5000 ind. L^?1 without affecting the mortality, confirming that attaining this high density in culture is possible. However, egg harvest reached an optimum of 12 000 egg L^?1 day^?1 at ~2500 ind. L^?1 indicating that increasing stocking density above this level is not of practical interest. Calculations showed that the loss in egg harvest at stocking densities <2500 ind. L^?1 is of 1.3% for every additional 100 adult copepods L^?1. The increasing adult density did not affected the proportion of DHE produced (~10% of harvest) but decreased significantly the HS, though not to a point that would be problematic in a commercial production. Understanding the biology of copepods when stocked at high density is important to improve copepod culture systems and increase egg harvest yields. Technical solutions such as the continuous separation of eggs from adults in the water column, recirculation and the continuous provision of food are seen as potential solutions.     

Effect of combined fish meal : soybean meal ratio,vitamin C and fish oil supplementations in diet on the growth and reproduction of red swamp crayfish,Procambarus clarkii (Crustacea: Decapoda)

Fish meal (FM), vitamin C (VC) and fish oil (FO) play important roles in the growth and reproduction in aquatic animals. To determine the optimum dietary combinations of FM:SM (soybean meal) ratio, VC and FO supplementations for the growth and reproduction of female crayfish Procambarus clarkii, we used the L9 (3³) orthogonal array, which arranged three factors varied at three levels (FM:SM at 1:3, 1:2 and 1:1.5; VC supplementation at 0.02%, 0.04% and 0.06%; FO inclusion at 1.90%, 2.85% and 3.80%). Range analysis showed that the highest weight gain (WG) of the crayfish occurred at FM:SM of 1:1.5, VC supplementation of 0.04% and FO inclusion of 1.90%, and the maximum gonadosomatic index (GSI), egg laying amount (ELA) and spawning rate (SR) were obtained at FM:SM 1:1.5, VC supplementation 0.06% and FO inclusion 3.80%. Analysis of variance indicated that all the three factors had no significant effects on WG. Fish oil supplementation significantly affected GSI, ELA and SR (P<0.05), while FM:SM did not significantly influence any of these indicators. Taking the cost into consideration, we suggest that a dietary FM:SM of 1:3, VC supplementation 0.06% and FO inclusion 3.80% might be the optimal combinations for the reproduction of P. clarkii.     

Influence of dietary linoleic acid (18:2n‐6) and α‐linolenic acid (18:3n‐3) ratio on fatty acid composition of different tissues in freshwater fish Songpu mirror carp,Cyprinus Carpio

Six isonitrogenous and isoenergetic purified diets were formulated to feed Songpu mirror carp for 60 days. The control diet (CD) was only supplemented with soybean oil. The other five experimental diets contained soybean oil, linseed oil and lard oil blended at various inclusion levels to attain different linoleic acid (LA)/α‐linolenic acid (LNA) ratios (0.53, 1.04, 2.09, 3.95, 6.82) with a constant total C₁₈ polyunsaturated fatty acids (PUFA; LA+LNA, 2% dry weight) content. The fatty acid (FA) profiles of hepatopancreas, dorsal muscle, intestine, intraperitoneal fat (IPF), spleen and kidney reflected those of the diets, but with some differences. The spleen showed the lowest correlation with diet compared with other tissues, followed by the hepatopancreas (P < 0.05). The intestine and IPF showed relatively higher correlation. On the other hand, the control group had the lowest tissue‐diet correlation, followed by the LA/LNA0.53 group (P < 0.05), whereas the LA/LNA2.09 showed the highest. The LA/LNA ratios in the tissues were up‐regulated in the LA/LNA0.53, 1.04 groups and down‐regulated in the LA/LNA3.95, 6.82 groups. This was due to when LA (or LNA) was highly added in diet, the decrease in this FA was huge in tissue. The contents of saturated fatty acids and monounsaturated fatty acids increased in the control group, but seemed not influenced by dietary LA/LNA ratios. These results demonstrated that the FA deposition was tissue‐specific, and also influenced by the dietary FA composition in the experimental fish. Finally, we suggest that 2.09 is the optimal LA/LNA ratio (2% C₁₈ PUFA) of Songpu mirror carp for fillet FA composition.     

N.M. Kelly,M. Fonseca and P. Whitfield, ‘Predictive mapping for management and conservation of seagrass beds in North Carolina’. Aquatic Conservation: Marine and Freshwater Ecosystems11(6) 2001,437–451

The original article to which this Erratum refers was published in Aquatic Conservation: Marine and Freshwater Ecosystems 11(6) 2001, 437–451.     

Otolith–fish size relationship in juvenile gag (Mycteroperca microlepis) of the eastern Gulf of Mexico: a comparison of growth rates between laboratory and field populations

In this study, we conducted experiments on wild-caught juvenile gag Mycteroperca microlepis from the eastern Gulf of Mexico to evaluate the effect of food availability on somatic growth and otolith growth. Juveniles were fed at two different food levels until all fish attained similar sizes. We found that food availability significantly affected growth rates. However, we also found that this manifested itself in differential otolith size. That is, slower-growing gag had larger, heavier otoliths than equal-sized faster-growing gag; an experimental result that has been observed previously among various fish species. We wanted to apply these experimental results to field-caught gag because our initial observations indicated that gag from more southern latitudes along Florida’s west coast were larger than gag from more northern latitudes, at least during the early juvenile period. Applying these relationships to regional field populations, we found that juvenile gag from the more northern latitudes appeared to grow faster than those from southern latitudes, using an otolith–fish size proxy for growth. However, examination of fish length–age relationships revealed that juvenile gag growth rates were not significantly different between regions. These results are contrary to the expectation that larger-sized gag from southern latitudes are growing faster, and suggests that other factors, such as spawning time and habitat quality may explain regional size differences.     

Development of piscirickettsiosis in Atlantic salmon (Salmo salar L.) smolts after intraperitoneal and cohabitant challenge using an EM90‐like isolate: A comparative study

Piscirickettsiosis, caused by the intracellular Gram‐negative bacteria Piscirickettsia salmonis, is at present the most devastating disease in the Chilean salmon industry. The aim of this study was to analyse disease development after challenge with a P. salmonis strain (EM90‐like) under a controlled environment by comparing intraperitoneal challenge with cohabitation challenge. The P. salmonis EM90‐like isolate was cultured in a liquid medium for the challenge of 400 Atlantic salmon (Salmo salar) smolts. Cumulative mortality was registered, necropsy was performed, and bacterial distribution in the tissues and histopathological changes were analysed. The results revealed a similar progression of the disease for the two different challenge models. Pathological and histopathological changes became more visible during the development of the clinical phase of the disease. Bacterial DNA was identified in all the analysed tissues indicating a systemic infection. Bacterial tropism to visceral organs was demonstrated by real‐time quantitative PCR and immunohistochemistry. Better knowledge of disease development during P. salmonis infection may contribute to further development of challenge models that mimic the field situation during piscirickettsiosis outbreaks. The models can be used to develop and test future preventive measures against the disease.