Stress mitigating and growth enhancing effect of dietary tryptophan in rohu (Labeo rohita,Hamilton, 1822) fingerlings

An experiment was conducted to study the stress mitigation and growth enhancing role of dietary l-tryptophan (TRP) under thermal stress in rohu, Labeo rohita fingerlings for 45 days. Seven hundred and twenty fishes were distributed in three major groups that are ambient temperature (26 °C), 34 and 38 °C in triplicate following a complete randomized design. Acclimation of fishes to 34 and 38 °C over average ambient temperatures were carried out at 1 °C/day. Each group was fed with a diet supplemented with 0, 0.36, 0.72 or 1.42 % l-TRP. Results showed that blood glucose and serum cortisol level were found to be significantly higher (p < 0.05) in the higher temperature groups than the ambient temperature group. Similarly, aminotransferase, lactate dehydrogenase, malate dehydrogenase, CAT, superoxide dismutase activities were found to be significantly higher (p < 0.05) in the control groups (0 % l-TRP) and decreasing activities of these enzymes were observed with the increasing level of dietary l-TRP. In different temperature groups, l-TRP-supplemented groups were found to have higher (p < 0.05) growth, RGR and PER. The results obtained in the present study indicate that dietary l-TRP mitigates thermal stress and enhances growth. From the present study, we can conclude that dietary supplementation of l-TRP at the 0.72 % level in the diet is found to be optimum to reduce thermal stress even up to 38 °C in rohu, L. rohita. The baseline data obtained here could be useful for the farmers to formulate feeds to culture the fish in different agro-climatic zones.     

ATP depletion inhibits retraction of chromatophores induced by GABA in cephalopod Todarodes pacificus

Color changes in cephalopods are generated by the expansion or retraction of chromatophores located under the dermis. The behavior of the chromatophores is regulated by neurotransmitters; l-glutamate (l-Glu) is an excitatory transmitter that causes the chromatophores to expand. To date, serotonin [5-hydroxytryptamine (5-HT)] is the only neurotransmitter known to stimulate retraction of chromatophores. We found that the chromatophores in the Japanese squid Todarodes pacificus were regulated by γ-aminobutyric acid (GABA), an inhibitory neurotransmitter, and that GABA caused expanded chromatophores to retract. We also found that adenosine 5′-triphosphate (ATP) concentrations in skin samples remained stable at their initial values for more than 24 h after the death of each squid; therefore, the chromatophores could respond to both l-Glu and GABA during that period. Furthermore, we attempted to reduce the levels of ATP by storing skin sample in sodium azide solution. The chromatophores in sodium azide-treated skin samples were induced to expand by l-Glu, but these expanded chromatophores could not be induced to retract by GABA. Based on these observations, we conclude that ATP is essential for retraction, but not expansion, of chromatophores.     

Detection of the first lectin with antimicrobial activity present in serum of the Amazonian fish tambaqui Colossoma macropomum

Tambaqui Colossoma macropomum is the most important Amazonian native species in South American aquaculture. Innate immunity at least partially depends on the recognition of pathogen-associated molecular patterns by receptor-recognizing pathogens (PRRs). Some PRRs have been characterized in fishes, and several studies have focused on the role of lectins in the immune system of various fishes. Lectins are proteins that specifically recognize carbohydrates and which have important biological functions. Tambaqui serum lectin (ComaSeL), which was identified on the basis of its hemagglutinating activity, was pre-purified, biochemically characterized, and used in assays of antibacterial activity against pathogenic bacteria in freshwater fishes. A study of the seasonality of this lectin was performed. Comasel activity was stable at a pH between 4.0 and 9.0 and lost 100?% of its activity at 70?°C. It recognized the carbohydrates d-galactose, 1-O-methyl-d-galactopyranoside, and d-fucose, showing antibacterial activity for Gram-negative bacteria. Its activity showed significant differences between the summer and winter (p?<?0.05, Tukey test), thereby corroborating observations that tambaqui becomes more susceptible to mortality from diseases caused by bacteria and fungi during the winter. With this information, new tools may be developed for gaining a better understanding of the role of these proteins in the immune system of the tambaqui, ultimately resulting in the improved management of this fish by pisciculturists.     

Purification and characterization of trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides

Trypsin from the pyloric ceca of orange-spotted grouper, Epinephelus coioides, was purified by fractionation with ammonium sulfate, ionic exchange, and affinity chromatography. The protein was purified 161.85-fold with a yield of 4%. Purified trypsin had an apparent molecular weight of 24 kDa according to an SDS-PAGE analysis. Optimal profiles of temperature and pH of the enzyme were 50°C and 8–10, respectively, using Nα-benzoyl-l-arginine ethyl ester as the substrate. The results of thermal and pH stability assays showed that the enzyme was stable at temperatures of up to 50°C and in the pH range of 6–8. Trypsin activity decreased with an increasing NaCl concentration (0–0.6 M). The activity of purified trypsin was effectively inhibited by a soybean trypsin inhibitor and N-p-tosyl-l-lysine chloromethyl ketone, and was slightly inhibited by iodoacetic acid, ethylenediaminetetraacetic acid, 1-(l-trans-epoxysuccinyl-leucylamino)-4-guanidinobutane, and pepstatin A. Protein identification of the purified protease showed that the sequences of two peptides, LGEHNI and NLDNDIML, were highly homologous to other fish trypsins. The measurement of trypsin activity in different tissues showed that the highest activity was detected in pyloric ceca, followed by anterior intestine, middle intestine, hind intestine and spleen, but very low activities were found in other tissues. An inverse relationship between the trypsin activity in four tissues of pyloric ceca, anterior intestine, middle intestine and hind intestine and fish body weight as a result of increased pepsin in stomach indicated grouper growth status was increased.     

Rhamnose-binding lectins induce respiratory burst activity in macrophage cells from rainbow trout

Rhamnose-binding lectins (RBLs) have been isolated and characterized from various kinds of fish. RBLs recognize the structures of lipopolysaccharides and lipoteichoic acid on microbes, and have an opsonic effect, suggesting that RBLs play an important role as pattern recognition proteins in innate immunity. However, the function of RBLs in the removal of pathogens from the body has not yet been elucidated. In this study, we investigated the effect of three RBLs—named CSL1, 2, and 3—that were isolated from chum salmon Oncorhynchus keta eggs on the respiratory burst activity in a macrophage cell line. The CSLs induced reactive oxygen species in the peritoneal macrophage cell line from rainbow trout Oncorhynchus mykiss (RTM5). However, this activity was not affected by l-rhamnose or dl-threo-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol, an inhibitor for glucosylceramide synthesis, indicating that the interaction between CSLs and Gb3 on cell surfaces was not involved in the induction of respiratory burst activity.     

Culture-independent analysis of the bacterial community during fermentation of pa-som,a traditional fermented fish product in Laos

Pa-som is a traditional salty fermented food made from varieties of freshwater fish with garlic and rice in Laos. A similar product, plaa-som, is made in Thailand. To investigate the fermentation process of pa-som, lactic acid production and pH were monitored during laboratory-scale production of pa-som. Furthermore, the variety of bacteria involved and their succession during fermentation were examined using culture-independent polymerase chain reaction (PCR) denaturing gel gradient electrophoresis targeting the 16S ribosomal RNA (rRNA) gene. d- and l-lactic acid production and a decrease in pH were observed in the samples after 1 day of fermentation. The lactic acid content and pH continued to increase and decrease, respectively, until 4 days of fermentation. Overall, six lactic acid bacteria and eight other indigenous bacteria species were detected during pa-som fermentation. Among the lactic acid bacteria detected, two Lactococcus and one Weissella species were detected in samples after 1–4 days of fermentation, suggesting that these three species play major roles in pa-som fermentation from the initial phase. This is the first report to investigate the fermentation process in pa-som at the microbial level. This research approach should be applicable to a wide variety of pa-som and related fermented fishery products in Laos to help understand their microbial diversity and to identify beneficial bacterial species for improving quality.     

Effects of <Emphasis Type="SmallCaps">l</Emphasis>-carnitine against H<Subscript>2</Subscript>O<Subscript>2</Subscript>-induced oxidative stress in grass carp ovary cells (<Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>)

This study was designed in vitro to investigate the effects of l-carnitine against H₂O₂-induced oxidative stress in a grass carp (Ctenopharyngodon idellus) ovary cell line (GCO). GCO cells were pre-treated with different concentrations of l-carnitine, followed by incubation with 2.5 mM H₂O₂ for 1 h to induce oxidative damage. The results indicated that adding l-carnitine at concentrations of 0.01–1 mM into the medium for 12 h significantly increased cell viability. Pre-treatment with l-carnitine at concentrations of 0.1–5 mM for 12 h significantly inhibited 2.5 mM H₂O₂-induced cell viability loss. The significant decreases in the level of reactive oxygen species and cell apoptosis were observed in 0.5 mM l-carnitine group compared to the H₂O₂ group. Malondialdehyde values of all of the l-carnitine groups were significantly lower than those of the H₂O₂ group, while total glutathione levels of all of the l-carnitine groups were significantly higher than of the H₂O₂ group. The activity of antioxidant enzymes, such as total superoxide dismutase (0.1 and 0.5 mM l-carnitine), catalase (0.5 mM l-carnitine) and γ-glutamyl cysteine synthetase (0.5 and 1 mM l-carnitine), was significantly increased. In addition, pre-treatment of l-carnitine in GCO cells exposed to 2.5 mM H₂O₂ significantly increased the mRNA expression of copper, zinc superoxide dismutase, catalase (0.5 mM l-carnitine), glutamate cysteine ligase catalytic subunit (0.1–1 mM) and glutathione peroxidase (0.1 mM l-carnitine). In conclusion, l-carnitine promotes GCO cell growth and improves antioxidant function, it plays a protective role against oxidative stress induced by H₂O₂ in GCO cells, and the appropriate supplemental amount of l-carnitine is 0.1–1 mM.     

Novel method for improving the antioxidative properties of fish meat by direct injection of sodium l-ascorbate into the blood vessels of live fish

The color of the red muscle of pelagic fish is used as an indicator of freshness, and sustaining a bright red color is important for maintaining the commercial value of pelagic fish. Feeding fish with antioxidant compounds can delay metmyoglobin (metMb) formation, but the process requires long-term feeding. Live cultured Japanese horse mackerel Trachurus japonicus were used in this study. After anesthetization, 2 ml of blood was drawn from blood vessels, and a parenteral solution including an antioxidant compound was injected. Browning, metMb formation, and lipid oxidation of dark muscle during chilled storage were delayed by injecting sodium l-ascorbate as an antioxidant compound in the blood vessels of live fish.     

The optimal dietary level of ascorbic acid for juvenile Pacific bluefin tuna, Thunnus orientalis

A feeding experiment was conducted to evaluate the efficacy of, and determine the requirements for dietary AsA (l-ascorbic acid) using its popular derivative l-ascorbyl-2-monophosphate-Mg (APM) for juvenile Pacific bluefin tuna (PBT). The five test diets (with APM-0, -400, -800, -1200 and -1600) were prepared by adding 0, 400, 800, 1200 and 1600 mg of APM kg diet^?1, respectively. These diets, together with chopped sand lance (the control diet), were administered, in duplicate to 0.27 g PBT at 25 days after hatching (300 juveniles per 15 m³ tank). The PBT were fed to apparent satiety 6 times a day for 2 weeks. While final body weight, feed conversion and survival showed no differences among diets APM 400–1600, PBT fed APM-0 indicated lower growth performance together with anorexia, dark pigmentation and ataxia from 5 days and reached 80 % mortality at 12 days after the start of the feeding trial. In addition, liver and brain ascorbic acid (AsA) concentrations increased with increasing dietary APM levels, the values were similar in PBT fed diets with APM-1200 and APM-1600, and liver and brain concentrations of AsA were significantly higher in these fish than in the PBT fed the other diets (P < 0.05). The PBT responded to increasing dietary APM, and the fish fed APM-1200 had the highest weight gain, protein and lipid content. The data indicate that PBT can utilize APM as an AsA source and suggest that dietary supplementation with APM-1200 (454 mg AsA kg^?1 diet) would result in satisfactory growth.     

Embryonic development and influence of egg density on early veliger larvae and effects of dietary microalgae on growth of brown mussel Perna perna (L. 1758) larvae under laboratory conditions

The effect of egg density on embryonic development and larval quality as well as the lipid and fatty acid contents (eicosapentaenoic acid, EPA; docosahexaenoic acid, DHA) of cultured microalgae fed to Perna perna larvae was studied under controlled conditions to provide information needed for development of an experimental hatchery. Embryonic development followed the common sequence exhibited by other bivalves. d-larva stage was attained 40–44 h post-fertilisation at 21 ± 1 °C. The umbo-stage was reached in 11 days, and pediveliger larvae were observed 26 days post-fertilisation. Low egg density (range 20–100 eggs cm^?2) produced high proportions of normal d-larvae. Larval development showed two growth phases: 1st—the mixotrophic stage and 2nd—the exotrophic stage where the composition of diets had significant effects on larval growth with higher rates in larvae fed with the mixed microalgae (Isochrysis galbana + Chaetoceros calcitrans, I. galbana + Phaeodactylum tricornutum and I. galbana + Skeletonema costatum) in comparison with the monospecific diet (I. galbana). Fatty acid analysis showed that larval growth and survival were strongly influenced by proportions of dietary DHA and EPA. These results indicate that DHA and EPA are the key factors in determining larval performance, considerably more than the total amount of other fatty acids.     

Inactivation kinetics of formaldehyde on N-acetyl-β-d-glucosaminidase from Nile tilapia (Oreochromis niloticus)

Formaldehyde is a widely used sanitizer in aquaculture in China, while the appropriate concentration is not available to be used effectively and without damage to tilapia much less to its reproductive function. N-acetyl-β-d-glucosaminidase (EC 3.2.1.52, NAGase), hydrolyzing the oligomers of N-acetyl-β-d-glucosamine into monomer, is proved to be correlated with reproduction of male animals. In this paper, NAGase from spermary of tilapia was chosen as the material to study the effects of formaldehyde on its activity in order to further investigate the effects of formaldehyde use on tilapia reproduction. The results showed the relationship between the residual enzyme activity and the concentration of formaldehyde was concentration dependent, and the IC₅₀ value was estimated to be 3.2 ± 0.1 %. Appropriate concentration of formaldehyde leaded to competitive reversible inhibition on tilapia NAGase. Moreover, formaldehyde could reduce the thermal and pH stability of the enzyme. The inactivation kinetics of formaldehyde on the enzyme was studied using the kinetic method of substrate reaction. The inactivation model was setup, and the rate constants were determined. The results showed that the inactivation of formaldehyde on tilapia NAGase was a slow, reversible reaction with partially residual activity. The results will give some basis to determine the concentration of formaldehyde used in tilapia culture.     

Role of catecholamines and nitric oxide on pigment displacement of the chromatophores of freshwater snakehead teleost fish,Channa punctatus

We are reporting for the first time that the catecholamines (adrenaline and noradrenaline) inhibit the effect of nitric oxide (NO) on melanosome dispersion in freshly isolated scales of the freshwater snakehead fish, Channa punctatus. We studied the effect of NO and catecholamines on the pigment displacement by observing the changes in the melanophore index. The scales when treated with solution containing NO donor sodium nitroprusside (SNP) showed dispersion of melanosomes, whereas NO synthase blocker N-omega-Nitro-l-arginine suppresses this action of SNP. Treatment with adrenaline and noradrenaline on the isolated scales caused aggregation of melanosomes. Scales treated with solution containing catecholamines and SNP resulted in aggregation of melanosomes suggesting that catecholamines mask the effect of SNP. These results suggest that the catecholamines are inhibiting the effect of NO and causing the aggregation of the melanosomes may be via surface receptors.     

Dietary isoleucine requirement of fingerling catla, Catla catla (Hamilton), based on growth, protein productive value, isoleucine retention efficiency and carcass composition

In order to determine the dietary isoleucine requirement of fingerling catla, Catla catla (4.25 ± 0.15 cm, 0.61 ± 0.04 g), six isonitrogenous (33.0 % crude protein) and isocaloric (13.7 kJ/g digestible energy) amino acid test diets containing casein, gelatin and l-crystalline amino acids with graded levels of isoleucine (0.5, 0.75, 1.0, 1.25, 1.5 and 1.75 % of the dry diet) were prepared. Triplicate groups of fish were randomly stocked in eighteen 70-l indoor polyvinyl circular troughs at a density of 25 fingerling per trough provided with a water flow-through system (1–1.5 l min^?1). The experimental diets were fed to fish to apparent satiation at 08:00, 12:30 and 17:30 h for 12 weeks. Growth of the fish was found to increase with the incremental levels of dietary isoleucine up to 1.25 % of the dry diet. Quadratic regression analysis at 95 % maximum response of absolute weight gain (6.18 g fish^?1), protein productive value (0.32), isoleucine retention efficiency (71.91 g fish^?1), RNA/DNA ratio (4.81) and carcass protein (15.7 %) yielded the optimum isoleucine requirement in the range of 1.13–1.18 % of the dry diet, corresponding to 3.42–3.58 % of dietary protein. Data generated in this experiment would be useful to formulate isoleucine-balanced, cost-effective quality feeds for fingerling catla.     

The influence of \upbeta-hydroxy- \upbeta-methylbutyrate (HMB) on cell-mediated immunity in tench Tinca tinca (L.): in vitro and in vivo study

$\upbeta$ -Hydroxy- $\upbeta$ -methyl butyrate (HMB) has been shown to counteract many of the negative effects of intensive fish production methods and results in increased growth and protection against diseases. In the present study, the in vitro and in vivo effect of HMB on the immunocompetence cell activity in tench Tinca tinca (L.) was examined. In the in vitro study pronephric phagocytes and lymphocytes were isolated from the fish and grown in culture medium (RPMI-1640) containing 0, 0.1, 1, 5, 10, 25, 50 or $100\,\upmu$ g HMB cm^?3 of medium. The effects of HMB on the respiratory burst activity (RBA), the potential killing activity (PKA) and lymphocyte proliferation stimulated by concanavalin A (ConA) or lipopolysaccharide (LPS) were examined. The in vitro study showed that HMB increased the RBA and PKA of the phagocytes, compared to the medium over that of cells grown without HMB. Lymphocyte proliferation stimulated by ConA and LPS was also increased approximately when HMB was added to the culture medium at concentrations between 10 and $100\,\upmu$ g HMB cm^?3. In the in vivo study fish were fed daily with pellets containing HMB at doses 0, 10, 25 and 50 mg kg^?1 body weight day^?1. The study showed that HMB statistically increased the RBA and PKA and highest activity at 50 mg kg^?1 body weight day^?1 were observed. Also lymphocyte proliferation stimulated by ConA and LPS were maximally stimulated at dose 50 mg kg^?1 body weight day^?1. In conclusion, the current study shows that HMB could potentially improve immunocompetence cell activity in tench through increased cell proliferation and functionality.     

Stress inhibits insulin release induced by feeding and arginine injection in barfin flounder Verasper moseri

We evaluated the effect of stress and adrenaline injection on insulin release in barfin flounder Verasper moseri. Flounders were fed to satiation and then exposed to 30 min of stress (chasing using a blunt stick), beginning 15 min after feeding. Plasma insulin concentrations were measured using a time-resolved fluoroimmunoassay for barfin flounder insulin. Peak insulin concentrations in the stressed flounders (3.4 ± 1.0 ng/ml, mean ± SEM) were lower than in the control group (8.3 ± 1.7 ng/ml). Similarly, in flounders injected with l-arginine (Arg; 3.5 mmol/kg body weight), the most potent insulinotropic factor for flounders, insulin levels were lower for up to 5 h in individuals exposed to chasing stress. Furthermore, plasma insulin levels did not increase after injection with Arg followed by exposure to 10 min of stress. This was also true for flounders co-injected with Arg (20 nmol/kg body weight) and adrenalin instead of the chasing stress. We conclude that stress induces a powerful and extended inhibition of insulin release in flounders, even when the stress is acute. We hypothesize that this effect is mediated partly by adrenaline release. Our results provide insight into the deleterious effects of stress on growth.     

Chemical composition and physical properties of salted shrimp paste (Kapi) produced in Thailand

Chemical composition and physical properties of 11 salted shrimp pastes (Kapi) obtained from various places of Thailand were determined. Based on proximate composition, protein constituted the major component (29.44–53.27 %, dry wt. basis). All samples contained 22.77–35.47 % NaCl with A _w of 0.695–0.774. Various formal nitrogen contents (11.96–22.87 mg N/g sample) were in agreement with different degrees of hydrolysis (12.68–20.76 %), suggesting the varying cleavage of peptides among the samples. From electrophoretic study, salted shrimp paste contained a large amount of small molecular weight proteins and peptides. Different samples had different colors with \( \Delta E^{*} \) of 47.10–60.43 and \( \Delta C^{*} \) of 9.46–20.76. The samples had total carotenoid content of 0.54–1.97 mg/g sample. Free astaxanthin, astaxanthin diester and canthaxanthin were the major carotenoids in salted shrimp paste. Thus, salted shrimp paste is a good source of protein and serves as the nutritious condiment.     

Sperm characteristics and androgens in Acipenser ruthenus after induction of spermiation by carp pituitary extract or GnRHa implants

Spermiation and changes in androgen (testosterone, T and 11-ketotestosterone, 11-KT) levels were studied in sterlet (Acipenser ruthenus) treated with GnRH agonist implants (dAla⁶-Pro⁹-LHRHa) at 25 and 75?μg?kg^?1 b.w. and compared with those males treated with 4?mg?kg^?1 b.w. of carp pituitary extract (CPE) and 3 pellets of Ovopel kg^?1 b.w., which contains dAla⁶-Pro⁹NEt-mGnRH and metoclopramide. Sperm quality (sperm mass, spermatozoa concentration and sperm motility and velocity) was evaluated 24, 48 and 72?h after hormonal treatments. Males did not release sperm in the control group injected with physiological solution, while sperm could not be collected 7?days after treatments in all hormonally treated groups. Spermiation rates were 100?% in the CPE and Ovopel groups and 25–50?% in the GnRHa-treated groups. Sperm production was significantly lower in the GnRHa-treated groups than in the CPE and Ovopel groups and decreased 72?h after hormonal treatment. Sperm motility and velocity were higher in the Ovopel and GnRHa (75?μg) groups compared to the CPE and GnRHa (25?μg) groups and decreased 72?h after hormonal treatment. Androgens were only affected in spermiating males and changed in the Ovopel and GnRHa (75?μg) after hormonal treatment. Significant correlations were observed between sperm production, sperm motility and sperm velocity, but not androgens. The present study suggests involvement of dopamine in sturgeon spawning. Additionally, better sperm quality observed in the Ovopel group and particularly sperm motility in the GnRHa (75?μg) suggests enhancement of sperm quality in sturgeon treated with GnRHa. Therefore, further study is needed to induce fully spermiation using GnRHa implants in combination with a dopamine inhibitor.     

Age, growth, and reproductive characteristics of dolphinfish Coryphaena hippurus in the waters off west Kyushu, northern East China Sea

The growth and reproductive characteristics of dolphinfish Coryphaena hippurus collected in the waters off western Kyushu from May 2008 to April 2011 were determined based on scale and otolith readings and gonad histological examinations, respectively. Based on annual increments in scales and daily increments in sagittal otoliths, the von Bertalanffy growth curves in male and females were determined as $ FL_{t} = 1049[1 - \exp \{ - 0.835(t + 6.975 \times 10^{ - 14} )\} ] $ and $ FL_{t} = 938[1 - \exp \{ - 1.029(t + 6.975 \times 10^{ - 14} )\} ] $ , respectively, where FL _t is the mean fork length (mm) at age t. The spawning period was found to last from June to August for dolphinfish, based on an examination of the monthly changes in the gonadosomatic index and histological observations. Therefore, based on the relationship between the fork length and the developmental stage of the testes or ovaries, male and female dolphinfish were found to reach sexual maturity by the following spawning season after hatching in the northern East China Sea.     

Production efficiency in New England’s oyster aquaculture industry

In coastal New England, growing oysters is a long-established practice that has exhibited a renaissance over the past few decades (Lapointe, Northeast region ocean council white paper: Overview of the aquaculture sector in New England, 2013). This industry generates millions in annual revenue, significantly boosting the economies of many coastal communities (Augusto &; Holmes, 2015 Augusto, K. &; Holmes, G. (2015). Massachusetts shellfish aquaculture economic impact study. Woods Hole, MA. Retrieved from http://web.whoi.edu/seagrant/wp-content/uploads/sites/24/2015/01/MA-Aquaculture-Economic-Impact-Study-2015.pdf [Google Scholar]). However, oyster aquaculture has received relatively little attention from the field of economics. To our knowledge, this study represents the first evaluation of productive efficiency among oyster producers in the United States and the first comparison of oyster production methods used in this country. Our findings indicate significant potential to increase productivity by reducing inefficiency in oyster production. However, industry-wide production efficiency has been increasing between 2013 and 2015. Further analysis revealed several factors that significantly influence inefficiency in oyster production, including a grower’s education level, location and farm diversification. This study provides insights into inefficiency in oyster production, enabling governance bodies and outreach specialists to make more informed decisions regarding this industry.     

Stochastic modeling of production risk and technical efficiency of Thai koi (Anabas testudineus) farming in Northern Bangladesh

Thai koi is one of the high commercially valued farm fishes which have expanded tremendously in the northern part of Bangladesh. However, despite its impressive growth in the initial years, output of the industry is highly volatile across different years and farms. This research, following the Just and Pope framework, has made use of Kumbhakar’s (2002 Kumbhakar, S.C. (2002) Specification and estimation of production risk, risk preferences, and technical efficiency. American Journal of Agricultural Economics, 84, 8–22.[Crossref], [Web of Science ®] , [Google Scholar]) extended stochastic frontier model (SFM) to estimate production risk and technical efficiency (TE) in Thai koi farming. Results show that feed is the most important input significantly influencing production. Zeolite and pesticide appear to be risk-reducing, while fingerlings, labor, feed and salt turn out to be risk-increasing inputs. The inefficiency model indicates that labor and pond area significantly reduce the technical inefficiency. Feed, fingerling and lime also act as TE-improving factors. Education of farmers improves TE, while experience, training and frequency of water change do not impact the TE. The mean TE scores are 0.73 and 0.96 for the flexible risk estimate and conventional SFM estimates, respectively. TE values appear to become exaggerated when production risk is excluded from the model. SFM recognizes that risk is involved in Thai koi farming that causes lower TE.