Cypermethrin and λ-cyhalothrin induced alterations in nucleic acids and protein contents in a freshwater fish, <Emphasis Type="Italic"> Channa punctatus</Emphasis>

In this study, a freshwater fish Channa punctatus was exposed to subacute concentrations of synthetic pyrethroid insecticides (cypermethrin and λ-cyhalothrin) for 96 h to evaluate their impact on the levels of nucleic acids and protein in its different organs. Significant enhancement in the level of DNA was recorded in all tissues of the fish at high concentration of cypermethrin, whereas RNA and protein contents increased in tissues at all concentrations of cypermethrin tested. In contrast, λ-cyhalothrin treatment caused an increase in the level of DNA only in liver and brain, whereas increase of RNA and protein varied to different levels in different tissues. Cypermethrin treatment induced RNA/DNA ratio in all fish organs tested, whereas λ-cyhalothrin caused a sharp decrease in the ratio. Protein/DNA ratios were found to be tissue specific in treatments with both of the insecticides. The results clearly indicated that both of these pyrethroids exerted their effects in a similar manner in fish liver but differed in other tissues. These insecticides acted as potential biomodulators in C. punctatus, though following different routes. The results may be an indicator of aquatic pollution affecting freshwater fauna and flora and thus signaling the need for strict regulation on the indiscriminate input of pyrethroids from agricultural sites.     

Comparison between α-LNA and DHA in early developmental stages of <Emphasis Type="Italic">Takifugu obscurus</Emphasis> and <Emphasis Type="Italic">Takifugu rubripes</Emphasis>

ABSTRACT:   Rearing experiments were conducted to investigate the essential fatty acid requirements in the early developmental stages of river puffer Takifugu obscurus and tiger puffer T. rubripes using two n-3 series unsaturated fatty acids, α-linolenic acid (18:3n-3, α-LNA) and docosahexaenoic acid (22:6n-3, DHA), under salinity of 30 and 18.5–20.3°C. River and tiger puffer larvae used in this study were 15 and 14 days old after hatching, and their average body weights were 30.1 and 20.8 mg, respectively. The results on fatty acid requirements of these two species were evaluated from fish growth, survival, fatty acid composition of the fish body and activity test results. The DHA groups of both river and tiger puffer exhibited better survival and weight gain. However, there was no difference in the mean final body weights of river puffer between two dietary groups. Also, the DHA group of tiger puffer showed better results in the recovery test from anesthetic condition than that obtained in the LNA group. In an examination of the fatty acid compositions of the whole body, the LNA group containing no dietary DHA resulted in 0.5% DHA in tiger puffer and 1.1% DHA in river puffer . These results suggest that α-LNA from Artemia converted to eicosapentaenoic acid (20:5n-3, EPA) and to DHA successively by their fatty acid metabolism. Symptoms following essential fatty acid deficiency were not observed in any experimental groups. As river puffer did not represent a significant difference in the dietary effects between α-LNA and DHA treatment groups, its essential fatty acid requirement was assumed to be somewhat closer to that of the freshwater fishes in comparison with that of marine fishes, including tiger puffer.     

Effects of light and temperature conditions on the expression of GnRH and GtH genes and levels of plasma steroids in <Emphasis Type="Italic">Odontesthes bonariensis</Emphasis> females

In this study we examined the endocrine mediation between environmental factors (temperature and photoperiod) and the brain–pituitary–gonadal axis in females of pejerrey Odontesthes bonariensis. Changes in the expression of brain gonadotropin-releasing hormones (GnRHs) and gonadotropin (GtH) subunit [follicle stimulating-β (FSH-β), luteinizing hormone-β (LH-β), glycoprotein hormone-α (GPH-α)] genes, plasma gonadal steroids [estradiol (E₂) and testosterone (T)], gonadal histology, and gonadosomatic index (GSI) in adult females exposed to combinations of short-day (8 h) or long-day (16 h) photoperiods and low (12°C) or high (20°C) temperatures after winter conditions (8 h light, 12°C) were analyzed. Pejerrey females kept under the short photoperiod had low GSIs, and their ovaries contained only previtellogenic oocytes regardless of the experimental temperature. In contrast, females exposed to the long photoperiod had high GSIs and ovaries with vitellogenic oocytes at both temperatures. These fish also showed a significantly higher expression of sGnRH, pjGnRH, cGnRH-II (the three different GnRH variants found to date in the pejerrey brain), FSH-β, LH-β and GPH-α genes and plasma E₂ levels than those at the shorter photoperiod. No significant changes were observed in plasma T levels. Based on these results, we concluded that the increase in day length but not that of temperature triggers the maturation of pejerrey females after the winter period of gonadal rest and that this occurs by an integrated stimulation of the various components of the brain–pituitary–gonad axis.     

Galactooligosaccharide and a combination of yeast and β-glucan supplements enhance growth and improve intestinal condition in striped catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis> fed soybean meal diets

The effects of galactooligosaccharide (GOS) and a combination of yeast and β-glucan (YβG) supplementation of dietary soybean meal (SBM) on the growth and digestive performance of striped catfish Pangasianodon hypophthalmus were evaluated. Four isonitrogenous (30% protein) and isocaloric (19 MJ/kg diet) diets were formulated to contain 100% fish meal (FM) protein, 55% FM protein/45% SBM protein, FM-SBM supplemented with 1% GOS, and a combination of 1% yeast and 0.1% β-glucan, respectively. Each diet was fed for 12 weeks to three groups of 30 striped catfish fingerlings (average weight 16.45?±?0.07 g) maintained in circular fiberglass tanks (600 l). Growth, feed utilization, and muscle protein composition of fish improved significantly after supplementation with either GOS or YβG compared to the unsupplemented SBM diet, but were similar to those of fish fed the FM diet. Nutrient digestibility, digestive enzyme activities, villi and microvilli length were significantly increased in fish fed the supplemented SBM diets. The gut microbiota ranking profile showed that supplementing the SBM diet with YβG and GOS gave a ranking of Verrucomicrobia, Spirochaetes, Bacteriodetes, and Actinobacteria phyla similar to that of the FM diet. Thus, diet containing 45% protein from soybean supplemented with either GOS or YβG can be recommended to improve the growth and digestive performance of striped catfish.     

Curcumin analogue inhibits lipid peroxidation in a freshwater teleost, <Emphasis Type="Italic">Anabas testudineus</Emphasis> (Bloch)—an in vitro and in vivo study

The effect of a synthetic curcumin analogue (salicylcurcumin) on fish lipid peroxidation was investigated in both in vitro and in vivo conditions using a teleost model Anabas testudineus (Bloch). Curcumin analogue inhibited the formation of lipid peroxidation products and thiobarbituric acid reactive substances (TBARS) content at the three concentrations (10⁻² M, 10⁻³ M and 10⁻⁴ M) in vitro. TBARS content was reduced by 80% in the liver and 68% in brain by the higher concentration of salicylcurcumin. For in vivo study, salicylcurcumin (0.5%) was supplemented along with the basal feed for a period of 60 days. It produced a 60% reduction in liver TBARS content. The antioxidant enzyme superoxide dismutase (SOD) was stimulated, whereas catalase (CAT) and glutathione peroxidase (GPx) were inhibited. Glutathione (GSH) was reduced and glutathione reductase (GR) unchanged. Even though there was an increase in SOD activity, the CAT and GPx did not increase accordingly, maybe due to the direct scavenging of H₂O₂ by salicylcurcumin. The protein content also increased in the curcumin-fed animals, indicating a positive growth-promoting effect. Therefore, it would be beneficial to supplement salicylcurcumin along with the aquaculture feed in order to help the fish to cope with adverse conditions in the environment. This would increase the survival rate, disease resistance and ultimately the growth rate.     

Annual changes in ovarian development and plasma estradiol-17β level in reared female common Japanese conger, <Emphasis Type="Italic">Conger myriaster</Emphasis>

ABSTRACT:   Annual changes in the gonadosomatic index (GSI), oocyte diameter, gonadal histology and plasma estradiol-17β (E₂) levels were investigated in female common Japanese conger Conger myriaster in captivity. Juveniles were caught in September 1999 and reared in seawater at temperatures ranging from 10–20°C for 3 years. All fish were immature when captured in September 1999. GSI and oocyte diameter increased from October 2000, peaked between summer and autumn 2001, and bottomed-out in winter 2001. Plasma E₂ level also increased from October 2000, but remained high. The ovarian developmental stage was at the peri-nucleolus stage or the oil droplet stage until September 2000. Vitellogenesis started in October 2000 and oocytes progressed to the tertiary yolk globule stage by summer 2001. However, vitellogenic oocytes regressed in all females after autumn 2001. The neogenetic oocytes began to increase after November 2001 and ovarian development progressed in 2002 as they did in 2001, although maximum GSI in 2002 was half its 2001 value. These data indicate that ovarian development in the common Japanese conger has an annual periodicity, and that these congers may be able to spawn in multiple years under rearing condition.     

Diversification economies and efficiencies in a ‘blue-green revolution’ combination: a case study of prawn-carp-rice farming in the ‘<Emphasis Type="Italic">gher</Emphasis>’ system in Bangladesh

‘Gher’ farming is a unique system that incorporates the joint operation of three enterprises: freshwater prawn, fish and HYV rice and is expanding rapidly in the coastal regions of Bangladesh. In this paper we evaluate the performance of this unique system in terms of the existence of diversification economies (amongst the three integrated enterprises), scale economies and technical efficiency using a stochastic input distance function approach on a sample of gher farmers. The results reveal evidence of a diversification economy in the rice–carp combination. Economies of scale exist in the ‘gher’ farming system. The level of technical efficiency is estimated at 68% implying that a substantial 47% [(100−68)/68] of potential output can be recovered by removing inefficiency. Significant efficiency gains are made from diversification amongst these enterprises. Also, the education of farmers and the female labour input significantly improve efficiency whilst larger operation size reduces efficiency. The key policy implication is that the diversification of enterprises, particularly the rice–carp combination, is beneficial and should be promoted. Also investment in education and creation of a hired labour market for females would improve technical efficiency.     

Leptin and its receptor in turbot <Emphasis Type="Italic">Scophthalmus maximus</Emphasis>: cloning,characterization and expression response to ratios of dietary carbohydrate–lipid

In the present study, the full-length cDNA sequences of leptin (LEP) and its receptor (LEPR) from turbot Scophthalmus maximus were cloned. The cDNA of tLEP was 1126 bp in length encoding 157 amino acids. The amino acid sequence shared low identity with human LEP (18.8 %), but the three-dimensional structures of these two LEPs were strongly conserved. The deduced 1173-amino acid sequence of tLEPR was 28 % identical to human LEPR, and 82 % too range-spotted grouper LEPR, containing all functionally important domains conserved in vertebrate LEPR. Tissue distribution analysis showed that tLEP was abundantly expressed in brain, eyes and liver. The highest level of tLEPR mRNA was found in liver and kidney. After a 9-week feeding trial using diets with different ratios of carbohydrate–lipid (1:6, 1:2, 2:1 and 14:1), it was found that the increase in dietary carbohydrate-to-lipid ratios from 1:6 to 2:1 did not significantly influence tLEP and tLEPR expression in turbot liver (P > 0.05). The hepatic tLEP expression was significantly elevated in treatment with 14:1 dietary carbohydrate-to-lipid ratio (P < 0.05). The hepatic tLEPR mRNA level in group with 14:1 dietary carbohydrate-to-lipid ratio was significantly lower than that in 1:6 group (P < 0.05), but had no significant difference with the other two groups (P > 0.05). These results revealed the important relationship between dietary carbohydrate-to-lipid ratio and LEP expression in turbot.     

The changes in the biochemical compositions and enzymatic activities of rotifer (<Emphasis Type="Italic">Brachionus plicatilis</Emphasis>, Müller) and <Emphasis Type="Italic">Artemia</Emphasis> during the enrichment and starvation periods

The changes in the biochemical compositions and enzymatic activities of rotifer (Brachionus plicatilis) and Artemia, enriched and stored at 4°C temperature, were determined. The total starvation period was 16 h and samples were taken at the end of the 8th and 16th hours. In present study, the rotifer and nauplii catabolized a large proportion of the protein during the enrichment period. Lipid contents of both live preys increased during the enrichment period and decreased in nauplii and metanauplii throughout the starvation period but lipid content of the rotifer remained relatively constant during the starvation period. The changes observed in the amino acid compositions of Artemia and the rotifer were statistically significant (P < 0.05). The conspicuous decline the essential amino acid (EAA) and nonessential amino acid (NEAA) content of the rotifer was observed during the enrichment period. However, the essential amino acid (EAA) and nonessential amino acid (NEAA) contents of Artemia nauplii increased during the enrichment period. The unenriched and enriched rotifers contained more monounsaturated fatty acid (MUFAs) than polyunsaturated fatty acid (PUFAs) and saturated fatty acids (SFA). However, Artemia contained more PUFAs than MUFAs and SFA during the experimental period. A sharp increase in the amounts of docosahexaenoic acid (DHA) during the enrichment of the rotifer and Artemia nauplii was observed. However, the amount of DHA throughout the starvation period decreased in Artemia metanauplii but not in Artemia nauplii. Significant differences in tryptic, leucine aminopeptidase N (LAP), and alkaline phosphatase (AP) enzyme activities of Artemia and rotifer were observed during the enrichment and starvation period (P < 0.05). The digestive enzymes derived from live food to fish larvae provided the highest contribution at the end of the enrichment period. In conclusion, the results of the study provide important contributions to determine the most suitable live food offering time for marine fish larvae. Rotifer should be offered to fish larvae at the end of the enrichment period, Artemia nauplii just after hatching and before being stored at 4°C, and Artemia metanauplii at the end of the enrichment and throughout the starvation period.     

Biochemical Composition of Seminal Plasma and Annual Variations in Semen Characteristics of Jundiá <Emphasis Type="Italic">Rhamdia quelen</Emphasis> (Quoy and Gaimard,Pimelodidae)

This study investigated the composition of milt of the South American silver catfish (Rhamdia quelen) or jundiá. The semen was taken from jundiá in different periods during the four seasons. The biochemical composition of seminal fluid and the characteristics of sperm were analyzed. The semen quantity which can be extracted per fish in one day was 0.95 ± 0.08 ml during spring (maximum) and 0.24 ± 0.03 ml during winter (minimum). Sperm density (spermatocrit) showed higher values in the spring (75.1 ± 1.3%) decreasing slightly afterwards and reaching 63.0 ± 2.4% to 65.0 ± 2.2% in the fall and winter. Immediately after water dilution, 90–100% of the spermatozoa presented vigorous straightforward motility that remained for at least 20 s. The total duration of the motility was 47.9 ± 1.3 s in the spring and 38.6 ± 0.6 s in the other seasons (P < 0.05). This pattern of motility is maintained for more than 2 h after storage of the milt at room temperature. The pH from 5 to 10 of the water dilution does not influence the sperm motility. The mean seminal pH and osmolality values were 8.7 ± 0.07 and 274.8 ± 11.2 (mOsm/kg), respectively. The ion concentration was: Na 153.7 ± 2.4, K 10.7 ± 2.4, Cl 139.4 ± 2.1, Ca 4.2 ± 0.2, Mg 0.9 ± 0.05, P 0.9 ± 0.08 (mEq/l). The total protein was 0.6 ± 0.05 mg/dl and cholesterol concentration was 13.9 ± 0.9 mg/dl.     

Do by‐catch reduction devices in longline fisheries reduce capture of sharks and rays? A global meta‐analysis

By‐catch in marine fisheries, particularly those using pelagic and demersal longlines, is a major driver of declines in abundance of sharks and rays around the world. A wide variety of by‐catch reduction devices (BRDs), that is, modified gears designed to reduce incidental captures of a variety of marine species while maintaining target catch rates, have been proposed, but the extent to which BRDs actually reduce the risk of catching sharks and rays remains unclear. We performed a meta‐analysis of 27 publications that reported the capture of sharks and rays and, in some cases, of targeted teleosts in longline gear deployed with and without BRDs. The risk of shark and ray capture differed between types of BRDs, but only one BRD type, longlines raised off the bottom, reduced by‐catch significantly. Circle hooks did not reduce the risk of capturing sharks and rays but might improve discard survival and are inexpensive, which might make them effective in reducing the detrimental effects of longlining on these species. In addition to being generally ineffective, some devices, such as electropositive and magnetic repellents, are expensive and have inherent construction drawbacks that are likely to make them unsuitable for commercial use. Overall, most BRDs did not affect the likelihood of catching targeted teleosts, but a substantial number of studies did not adequately assess target catch. We identified two poorly studied classes of BRD gear (i.e. raised demersal longlines, and monofilament nylon leaders), which represent promising directions for future research.     

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker <Emphasis Type="Italic">Miichthys miiuy</Emphasis> larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.     

Nucleotide sequence and mRNA expression analysis of <Emphasis Type="Italic">β</Emphasis>-actin gene in the orange-spotted grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis>

The full-length cDNA, encoding the orange-spotted grouper β-actin and spanning 1920 bp including a poly (A) tail, was cloned from its brain cDNA library. The open reading frame encodes a protein of 375 amino acids. Sequence analysis indicated that it contained the typical structural features of cytoplasmic actins, and showed higher homology with other vertebrate β-actin than any other members of the actin family. The partial genomic sequence indicated that the organization of the β-actin gene in the orange-spotted grouper might also be conserved. Northern blot analysis indicated that it was expressed at high levels in the brain, spleen, adipose tissue, ovary, and liver, but at low levels in the gill filament and heart, and at a very low level in the kidney. The expression of β-actin gene in the skeletal muscle was barely detectable. These results indicated that the expression of the orange-spotted grouper β-actin gene showed significant variation in different tissues. Therefore, caution should be taken when using β-actin gene as an internal control in the normalization of gene expression among tissues. Whereas, semi-quantitative RT-PCR analysis indicated that treatment with 17α–methyltestosterone (MT) had little effect on the mRNA expression of β-actin gene in the in vitro incubated hypothalamus, pituitary, and ovary fragments of the orange-spotted grouper, suggesting β-actin can be used as an internal control for RT-PCR analysis of MT effects on gene expression in these tissues.     

Experimental infection of <Emphasis Type="Italic">Betanodavirus</Emphasis> in freshwater fish <Emphasis Type="Italic">Gambusia affinis</Emphasis> (Baird and Girard, 1853)—a potential infection model for viral encephalopathy and retinopathy

Betanodaviruses are the causative agents of the disease known as viral nervous necrosis (VNN) or viral encephalopathy and retinopathy (VER) in a variety of marine and freshwater fish species. The aim of this study was to demonstrate experimental infection of an isolate of betanodavirus (RGNNV genotype) in freshwater fish, Gambusia affinis, for elucidation of transmission mechanism and potential use as a laboratory model. Morbidity and mortality rate was significantly higher by injection route of infection as compared to immersion by bath and resembled the natural infection of juvenile marine fish. The fish in disease affected group showed severe neurological disorders accompanied by extensive vacuolar degeneration and mild to moderate neuronal necrosis of the brain in comparison to control. Amplification of ~?427 bp product in the variable region of the coat protein gene of betanodavirus was achieved by RT-PCR with 100% sequence homology to RGNNV genotype.     

Are coping styles consistent in the teleost fish <Emphasis Type="Italic">Sparus aurata</Emphasis> through sexual maturation and sex reversal?

Individual differences in behaviour and physiological responses to stress are associated with evolutionary adaptive variation and thus raw material for evolution. In farmed animals, the interest in consistent trait associations, i.e. coping styles, has increased dramatically over the last years. However, one of limitations of the available knowledge, regarding the temporal consistency, is that it refers always to short-term consistency (usually few weeks). The present study used an escape response during a net restraining test, previously shown to be an indicative of coping styles in seabream, to investigate long-term consistency of coping styles both over time and during different life history stages. Results showed both short-term (14 days) consistency and long-term (8 months) consistency of escape response. However, we did not found consistency in the same behaviour after sexual maturation when the restraining test was repeated 16, 22 and 23 months after the first test was performed. In conclusion, this study showed consistent behaviour traits in seabream when juveniles, and a loss of this behavioural traits when adults. Therefore, these results underline that adding a life story approach to data interpretation as an essential step forward towards coping styles foreground. Furthermore, a fine-tuning of aquaculture rearing strategies to adapt to different coping strategies may need to be adjusted differently at early stages of development and adults to improve the welfare of farmed fish.     

Identification,characterization of selenoprotein W and its mRNA expression patterns in response to somatostatin 14, cysteamine hydrochloride, 17β-estradiol and a binary mixture of 17β-estradiol and cysteamine hydrochloride in topmouth culter (<Emphasis Type="Italic">Erythroculter ilishaeformis</Emphasis>)

In this study, a selenoprotein W cDNA was cloned from topmouth culter (Erythroculter ilishaeformis), and it was designated as EISelW. The EISelW open reading frame was composed of 261 base pairs (bp), encoding 86-amino-acid protein. The 5′ untranslated region (UTR) consisted of 104 bp, and the 3′-UTR was composed of 365 bp. A selenocysteine insertion sequence (SECIS) element was found in the 3′-UTR of EISelW mRNA. The SECIS element was classified as form II because of a small additional apical loop presented in SECIS element of EISelW mRNA. Bioinformatic approaches showed that the secondary structure of EISelW was a β1-α1-β2-β3-β4-α2 pattern from amino-terminal to carboxy-terminal. Real-time PCR analysis of EISelW mRNAs expression in 17 tissues showed that the EISelW mRNA was predominantly expressed in liver, ovary, pituitary, various regions of the brain, spinal cord and head kidney. Study of intraperitoneal injection showed that the levels of EISelW mRNA in brain, liver, ovary and spleen were regulated by somatostatin 14 (SS14), 17β-estradiol (E2), cysteamine hydrochloride (CSH) and a binary mixture of E2 and CSH, dependent on the dosage. These results suggest that E2, SS14 and CSH status may affect tissues of selenium metabolism by regulating the expression of SelW mRNA, as SelW plays a central role in selenium metabolism.     

The differences in behavioral responses to a net obstacle between day and night in captive manatees; does entanglement happen at night?

Entanglement in fishing gear occurs in endangered manatees and may result in serious injury or death. Such incidents may happen more frequently at night when the animal’s visual sense is limited. In this study, we examined the differences in behavioral response of captive manatees to a net obstacle during light (day) and dark (night) periods. We used a plastic net as the obstacle, and video-recorded the manatees’ behavior. The experiments showed that captive manatees avoided the obstacle during the day more frequently than at night, which suggests that the manatees can perceive the obstacle more readily during light periods. However, there was no difference in the frequency of bumping or actively touching the obstacle between light and dark periods. The results suggest that the manatees can recognize the net obstacle even at night by purposely touching it, but they avoid it less frequently, and that entanglement during light periods may occur during accidental bumping, rather than from a failure to recognize it altogether.     

Are strain genetic effect and heterosis expression altered with culture system and rearing environment in the Portuguese oyster (Crassostrea angulata)?

Re‐ranking of strain additive genetic effect and heterosis expression in different culture environments is not well understood in shellfish species. This study was carried out to estimate the strain additive genetic and heterotic effects on harvest body weight in a 3 × 3 complete diallel cross involving three populations of Portuguese oyster (Crassostrea angulata), two populations from Cat Ba (RIA1) and Nam Dinh, northern Vietnam, and an imported stock from China. Strip spawning was applied to produce full‐ and half‐sib families simultaneously of nine cross‐combinations for performance testing at two locations (Cat Ba Island, Hai Phong city and Van Don Island, Quang Ninh province, Vietnam) using two culture systems (‘single seed’ and ‘cultch set’). A total of 7269 individual oysters were examined over a grow‐out period of 270 days. A linear mixed model was used to estimate strain additive genetic and heterotic effects for body weight at harvest. Ranking of strains based on their additive genetic effects did not differ between the locations and culture systems. The non‐additive genetic (heterotic) effects were low and not significantly different from zero for the traits studied among culture systems. There were no significant differences in levels of heterosis for harvest body weight between the two test environments or culture systems. Based on the non‐significant heterotic and large additive genetic effects among strains used for this study, a future breeding programme in this species (C. angulata), setting aside issues of diversity, could be based simply on choice among different strains based on their performance.