Detection of catfish off-flavour compounds by trained dogs

Six mixed‐breed dogs were trained to detect 2‐methylisoborneol and geosmin in laboratory‐prepared water. The three dogs most responsive to training were selected for further testing to measure their ability to detect these compounds at levels typical of the early stages of an ‘off‐flavour’ event in catfish pond culture. The dogs were given one out of five choices of off‐flavour and ‘on‐flavour’ water samples and were trained to sit at boxes containing off‐flavour sample tubes. At the lowest concentration tested, 10 ng L^?1 of the target compound, the mean correct responses for the three dogs were 37%, 43% and 67%. Additional testing was conducted using off‐flavour pond water samples containing known amounts of these two compounds that occurred naturally. Correct responses for off‐flavour samples varied from 30% to 95%, depending on the sample and the dog. On‐flavour samples were correctly identified with 96% accuracy for all dogs and all samples. Dogs may provide practical early detection of off‐flavour problems in catfish ponds.     

Low-density silver carp Hypophthalmichthys molitrix (Valenciennes) polyculture does not prevent cyanobacterial off-flavours in channel catfish Ictalurus punctatus (Rafinesque)

Silver carp Hypophthalmichthys molitrix (Valenciennes) were co‐cultured with channel catfish Ictalurus punctatus (Rafinesque) in 0.4 ha earthen ponds to determine the impacts of carp grazing on pond phytoplankton communities and cyanobacterial off‐flavours in catfish. Carp were stocked at densities of 0, 75, or 250 fish ha^?1 in seven replicate ponds per treatment. The mean chlorophyll a concentrations (a measure of phytoplankton standing crop) steadily increased in all treatments from about 100 μg L^?1 in April to more than 400 μg L^?1 by mid‐October. Silver carp had no affect (P>0.1) on chlorophyll a concentrations across all sampling dates (April though October) or for sampling dates late in the growing season (August–October) when the prevalence of cyanobacterial off‐flavours among catfish populations is usually greatest. Silver carp did not eliminate odour‐producing cyanobacteria from pond phytoplankton communities: on sampling dates in September and October, three to six ponds in all treatments contained populations of the odour‐producing cyanobacteria Oscillatoria perornata, Anabaena spp., or both. Failure of silver carp to eliminate odour‐producing cyanobacteria resulted in a relatively high incidence in all treatments of ponds with off‐flavoured catfish. On sampling dates in September and October, catfish in three to five ponds in each treatment were tainted with either musty (2‐methylisoborneol) or earthy (geosmin) off‐flavours. The presence of silver carp had no obvious effect on off‐flavour intensity: on each sampling date, at least three ponds in each treatment contained catfish described as distinctly to extremely off‐flavored. Apparently, hypertrophic conditions in catfish ponds overwhelm the effect of silver carp grazing at the low carp densities used in this study.     

罗非鱼不同养殖系统对产出效果及异味物质含量的影响

对鱼菜共生系统、底排污系统、底排污+鱼菜共生3种养殖系统的水质变化和罗非鱼产出效果进行了分析,并利用微波蒸馏-吹扫捕集-气相色谱质谱联用技术检测了各系统水体中和罗非鱼肌肉中异味物质的含量变化。经过12周的养殖实验,对终重、生物量、特定生长率、饵料系数、增重率等指标进行测量比较,结果发现,罗非鱼的产出效果从优到差依次为:鱼菜共生组、底排污+鱼菜共生组、底排污组、对照组;底排污+鱼菜共生系统水体中溶解氧在各时期均最高,其亚硝氮、氨氮含量在各时期均最低;底排污或鱼菜共生系统均能有效降低养殖水体中异味物质2-MIB和GSM含量;对照组罗非鱼肌肉中异味物质含量最高,2-MIB和GSM分别达到(0.67±0.02)μg/kg和(0.870±0.018)μg/kg,而底排污+鱼菜共生组罗非鱼肌肉中异味物质含量在各时期最低,2-MIB和GSM分别为(0.31±0.02)μg/kg和(0.53±0.042)μg/kg。结果表明,在罗非鱼精养池塘中,可通过底排污和鱼菜共生结合,降低水体中和罗非鱼体内异味物质的累积,提高其经济价值。     

Impact of weather on off-flavour episodes at a Louisiana commercial catfish farm

The catfish aquaculture industry is hampered by off-flavour events that affect timely fish sales. In this study, weather data were correlated with geosmin and 2-methylisoborneol (2-MIB) levels in 21 commercial pond's water samples. Samples were collected weekly for 44 weeks. The off-flavour compounds, geosmin and 2-MIB, were quantified using gas chromatography–mass spectrometry. Weather data were collected near the catfish farm and included maximum and minimum air temperature, rainfall, average wind velocity, maximum and minimum humidity, and maximum and minimum soil temperature. Geosmin was weakly and positively correlated with air and soil temperatures, and weakly and negatively correlated with wind velocity. 2-MIB was strongly and positively correlated with air and soil temperatures, moderately and negatively correlated with wind velocity, and weakly and positively correlated with maximum humidity. There were no bivariate relationships between rainfall, minimum humidity or pond size, and levels of either off-flavour compound. Using logistic regression, the best predictors for off-flavour status based on geosmin levels included minimum soil temperature, rainfall and minimum humidity. The best predictors for off-flavour status based on 2-MIB levels included minimum soil temperature and average wind velocity. Soil temperature and rainfall were risk factors for off-flavour, while humidity and wind velocity were protective factors.     

Water quality,waste production,and off-flavor characterization in a depuration system stocked with market-size Atlantic salmon Salmo salar

Land-based Atlantic salmon, Salmo salar, grow-out facilities utilize depuration to remediate off-flavor. Water used in this process is either discharged or repurposed as supply water in recirculating aquaculture systems (RAS). Both approaches require an understanding of water quality and waste production for water treatment decisions and compliance with pollution discharge standards; however, these data were lacking. Therefore, a study was carried out to characterize these parameters. To begin, 311 salmon (5–6 kg) originally cultured in freshwater RAS were stocked at 100 kg/m³ in an 18 m³ depuration tank. Feed was withheld 1 day before transfer and throughout the 7-day study period. Hours after stocking, total suspended solids (TSS), total phosphorus (TP), and total ammonia nitrogen (TAN) levels spiked, and concentrations declined thereafter. Delta TSS and TP were negligible by the end of the trial; however, TAN plateaued, indicating that salmon began to catabolize somatic tissue in the absence of feeding. Geosmin and 2-methylisoboreol levels in water and fish were low throughout the study. This research indicates that residual waste production occurs while depurating Atlantic salmon. Procedural refinements and recommendations were gleaned including locality for introducing depuration system water within RAS and extension of the feed withholding period before depuration.     

Effects of solids removal on water quality and channel catfish production in a biofloc technology production system

Total suspended solids control was evaluated in a channel catfish (Ictalurus punctatus) biofloc technology production system. Settling chamber flow rates were 0.9 (LO) or 2.9 (HI) L/min to reduce total suspended solids to 300 mg/L; solids were not removed from control tanks. Channel catfish yields (7.6–8.7 kg/m³) were not affected significantly, but control fish were skewed toward smaller size classes. Control treatment channel catfish tolerated 1,410 mg/L total suspended solids without adverse effects. LO- and HI-treatment fillet geosmin concentrations were high enough to be designated as off-flavor. Water quality results suggested that nitrification was affected by solids removal.     

Effect of stocking biomass on solids,phytoplankton communities,common off‐flavors,and production parameters in a channel catfish biofloc technology production system

The effect of initial channel catfish (Ictalurus punctatus, Rafinesque, 1818) fingerling biomass (1.4, 1.8, or 2.3 kg m^?3) on phytoplankton communities, common off‐flavours and stocker catfish production parameters was evaluated in biofloc technology production tanks. Stocker catfish size (145.5–172.6 g fish^?1) at harvest did not differ among treatments, but net yield increased linearly as initial biomass increased (R² = 0.633). Mean total feed consumption increased linearly with initial catfish biomass (R² = 0.656) and ranged from 10.7 to 15.8 kg m^?3. Total suspended solids (TSS) in all treatments increased linearly with total feed addition, and high TSS appeared to impact negatively daily feed consumption. Initial phytoplankton populations were dominated by small colonial green algae and diatoms, and later transitioned to populations dominated by a small, filamentous cyanobacteria and diatoms. Low, variable concentrations of 2‐methylisoborneol and geosmin were present in biofloc tank water during most of the study and two tanks yielded catfish with 2‐methylisoborneol or geosmin concentrations that might be classified as off‐flavour. One isolate of actinomycete was isolated sporadically from some biofloc tanks, but its abundance was not correlated with 2‐methylisoborneol concentration in tank waters. The microbial sources of 2‐methylisoborneol and geosmin in biofloc tanks remain unidentified.     

Effect of ethanol, clofibric acid and temperature on the uptake and elimination of 2-methylisoborneol in channel catfish (Ictalurus punctatus)

Off-flavor, due to organoleptic compounds such as 2-methylisoborneol (MIB), is the single largest detriment to the harvest, production and profit from the channel catfish aquaculture industry of the Southeastern United States. Methods to increase the metabolism and/or elimination of compounds like MIB would provide a means towards improving catfish rearing practices. Previous studies indicated one or more forms of cytochrome P450 monooxygenase (CYP) may be involved in the biotransformation and elimination of specific organoleptic compounds, such as 2-methylisoborneol (MIB). In order to determine the role of CYP in the elimination of MIB, various compounds that have been shown to modulate cytochrome P450 expression in catfish were administered before and after exposure to ¹⁴C-MIB. Uptake and elimination was monitored in fish over 24 and 48 h, respectively. Pretreatment with clofibric acid (100 mg kg^–1-gavage) which induces a CYP2K-like isoform, and ethanol (1.0% v/v-aqueous) a CYP2 represser, alone and with enhanced temperature (added 10 °C) failed to affect uptake of MIB. Pretreatment with these compounds and conditions also failed to enhance elimination of MIB from channel catfish. However, when fish were treated with 1.0% ethanol after MIB exposure (i.e., during depuration), beta elimination halflives were changed from 144±35 to 71±13 h. in sexually mature animals but unchanged (191±113) in juveniles. The failure of CYP-modulating agents to alter MIB elimination in catfish suggests MIB may not readily undergo Phase I oxidation via CYP. The enhanced elimination of MIB in adults by ethanol warrants further study as to its potential use in aquaculture in purging MIB and related compounds prior to fish processing.     

Evaluation of Diquat as a Potential Algicide for Controlling the Musty-Odor-Producing Cyanobacterium,Oscillatoria perornata,in Catfish Aquaculture Ponds

ABSTRACT

The synthetic herbicide diquat was applied to a catfish aquaculture pond containing a heavy bloom of the cyanobacterium Oscillatoria perornata(a major contributor to musty off-flavor in farm-raised catfish) in order to determine the effectiveness of diquat as a selective algicide to prevent musty off-flavor in cultured catfish. Levels of the musty-odor compound 2-methylisoborneol (MIB) and numbers of O. perornata were monitored. Results indicate that diquat is not useful as an algicide for controlling O. perornata in catfish aquaculture ponds, despite its usefulness in controlling other aquatic weeds.     

The evolution of farm management,production efficiencies,and current challenges to catfish production in the United States

Abstract

The catfish industry is the most successful aquaculture business in the US. The development and growth of the catfish industry has resulted in complex fish farm businesses that require intensive management. Technological innovations have resulted in increased yields (land use efficiency). However, in more recent years, productivity gains have not kept pace with the rate of increase in input costs. Increasing intensification of catfish production over time has been accompanied by increased use of debt capital that results in higher levels of financial risk. While still a profitable activity, real profit margins have declined as financial risk has increased. New technologies will likely continue to increase productivity over time. Market‐oriented agribusiness approaches to catfish marketing are likely to become the norm. The challenge for the catfish industry is to coordinate adoption of new higher‐cost technologies with demand increasing market development to sustain farm price levels.     

Family and genetic group effects for resistance to proliferative gill disease in channel catfish, blue catfish and channel catfish×blue catfish backcross hybrids

The severity of gill damage (percentage of gill lamellae with lytic lesions) was determined in juveniles from 10 USDA 103 line channel catfish Ictalurus punctatus full‐sib families, 10 channel catfish×blue catfish I. furcatus backcross hybrid (7/8 channel catfish, 1/8 blue catfish) full‐sib families and a mixed‐family group of blue catfish placed in a commercial catfish pond experiencing proliferative gill disease (PGD)‐related fish mortalities. An initial challenge was conducted with all families, and a second challenge was conducted using the two most susceptible (most gill damage) channel catfish and backcross hybrid families and the two most resistant (least gill damage) channel catfish and backcross hybrid families. In the initial challenge, percentage gill damage was not different between channel catfish (12.3%) and backcross hybrids (11.6%), but was lower in blue catfish (0.2%). Mean percentage gill damage in the second challenge was not different among resistant backcross hybrid families (6.9%), resistant channel catfish families (7.6%) and blue catfish (4.8%), but was higher in susceptible backcross hybrid and channel catfish families (19.0% and 11.9% respectively). The correlation among family means for gill damage from challenge 1 and challenge 2 was r=0.87. Consistent differences between channel catfish and blue catfish and between resistant and susceptible families within genetic groups for gill damage after PGD challenge suggest that there is a genetic component for resistance to PGD and that improving PGD resistance through selection may be possible.     

The ratio between digestible protein and digestible energy affects accumulation and depuration of geosmin and 2-methylisoborneol (2-MIB) in Japanese seabass (Lateolabrax japonicus) raised in a recirculated aquaculture system

Actinobacteria and cyanobacteria accounted for less than 1% of total of bacteria in water in a recirculated aquaculture system (RAS) during a 15-week feeding trial with 0.11-g Japanese seabass. Resulting concentration of geosmin and 2-methylisoborneol (2-MIB) in RAS water was 169 and 45 ng L^?1, sufficient to produce strong off-flavour. The seabass were fed diets with 42%, 45% and 49% protein, and each protein level was supplemented with 15% or 18% lipid. Accumulation of off-flavours was independent of diet in fatty ventral tissue. Dietary protein significantly reduced off-flavours in lean, dorsal tissue. This was mainly rationalized by linear reduction in 2-MIB in response to increasing DP/DE and a strong, 2nd degree polynomial response in geosmin. The ratio between geosmin and 2-MIB was slightly higher at the beginning of a 10-day period with clean water and fasting, than what was observed throughout depuration. 2-MIB remained between 0.2 and 1 µg kg^?1 in dorsal tissue throughout depuration. Geosmin in ventral tissue ranged from 10 to more than 30 µg kg^?1at the termination of the feeding period and was reduced to a range from 6 to 20 µg kg^?1 by depuration.     

Maturity stage and plasma testosterone levels are related to sperm production in blue catfish,Ictalurus furcatus.

A prediction equation for sperm production in blue catfish was developed by a forward step‐wise regression analyses based on five independent factors: body weight, total length, stage of maturation, gonadosomatic index and condition factor of individual mature blue catfish raised in earthen ponds. The stage of gonad maturity and plasma testosterone contributed significantly (P < 0.05) to the prediction equation (Sperm production per unit body weight = 2.51 × maturity ? 0.01 × testosterone ? 5.776, r = 0.62, P < 0.05). The stage of maturity was strongly associated (P < 0.05) with gonadosomatic index and sperm production. Improvements in prediction accuracy are needed to make this model a useful tool to identify higher sperm producing blue catfish to improve the efficiency of channel x blue hybrid catfish embryo production.     

Rearing of African catfish (Clarias gariepinus) and vundu catfish (Heterobranchus longifilis) in traditional fish ponds (whedos): Effect of stocking density on growth, production and body composition

African catfish (Clarias gariepinus) (initial body weight: 34.8 ± 4.8 g) and vundu catfish (Heterobranchus longifilis) (initial body weight: 39.1 ± 8.2 g) fingerlings were stocked at densities of 4, 6 or 8 fish m^− 3 in traditional fish ponds (whedos) constructed in the floodplain of the Oueme River (South Benin, West Africa), for 70 days from March to June 2005. Fish were fed twice a day with 34% crude protein feed formulated with locally available ingredients. The effects of stocking density were evaluated in growth responses, gross production and body composition. Water quality variables were similar (p > 0.05) in all compartments. Temperature and pH were at the optimum level for fish. Dissolved oxygen ranged from 0.9 to 1.2 mg l^− 1 during the experiment and secchi disc transparency was low (< 14 cm). In both species, growth responses increased with the increasing density, significantly in African catfish stocked at density of 8 fish m^− 3 compared to the other densities (4 and 6 fish m^− 3) but not significantly in vundu catfish. Production data ranged from 3.1 ± 0.5 to 22.8 ± 4.5 t ha^− 1 year^− 1 in African catfish and from 6.1 ± 1.2 to 15.1 ± 3.1 t ha^− 1 year^− 1 in vundu catfish. Production increased with increasing stocking densities but only significantly (p < 0.05) between the density of 8 fish m^− 3 and the other densities. In both species, carcass fat increased with increasing density (p < 0.05) while carcass protein and moisture decreased (p > 0.05). These results are important because they indicate that, as far as growth rate and production are concerned, African catfish is more profitable than vundu catfish for culture at high density in whedo.     

2-Methylisoborneol disposition in three strains of catfish: absence of biotransformation

2-Methylisoborneol (MIB) and structurally related terpenoid compounds are responsible for millions of dollars of lost revenue to catfish farmers. In an attempt to determine enzymatic pathways of biotransformation and elimination of MIB, the in vitro metabolism of MIB was examined in the Ulvade strain of channel catfish (Ictalurus punctatus). Although cytochrome P450 (CYP) activities were observed and correlated with expression of specific isoforms (i.e. steroid hydroxylation and CYP3A expression), no metabolites of MIB were observed. To determine whether extrahepatic biotransformation may be occurring the in vivo metabolism and disposition of ¹⁴C-MIB was examined in Uvalde, USDA-103 channel catfish, and a channel catfish X blue catfish (Ictalurus furcatus) hybrid species. Confirming in vitro hepatic studies, no metabolites were observed in plasma from animals treated with an intra-arterial dose of ¹⁴C-MIB. ¹⁴C-MIB elimination was predicted using a two compartment model in each strain of fish. There was no significant difference in terminal half-lives between strains but possible differences in total body clearance and apparent volumes of distribution which may be related to higher lipid content in the hybrids. Results of these studies indicate biotransformation has no involvement in MIB elimination and that other physiological processes may play a more significant role in MIB disposition within Ictalurid fish species.     

Design and development of a geothermal temperature control system for broodstock management of channel catfish Ictalurus punctatus

A control system was designed to raise and maintain water temperatures within 0.03-ha earthen ponds to a range conducive for spawning (24–30 °C) channel catfish Ictalurus punctatus. Heating was done during February 2001 to April 2001, when temperatures would have otherwise prohibited spawning (<24 °C). Temperature was increased from 10 °C (ambient) by 2 °C per day, and maintained at 27 °C, by the addition of geothermally warmed water (36 °C). The control system substantially increased the controllability and precision of heating ponds compared to manual operation. Systems were designed to control sets of four ponds. In designing this control system, consideration of biological constraints was essential. Reproduction in channel catfish is most strongly influenced by temperature. Because cold fronts are common during the winter and early spring (January–March), it was essential to ensure that pond temperatures did not fall below the range for spawning. Constraints on the heating rate and temperature variability to maintain fish health and stimulate spawning behavior were considered. Components of the control system included temperature measurement devices (type-T thermocouples), a central electronic control unit, electronic switches and electrically actuated ball valves. In response to the temperature sensed by each thermocouple, the controller sent a message to close or open the valve. When the valve was opened, warm water was added to the pond to increase the average pond temperature. Hardware and algorithm design and initial system testing were the major components of this project. The final design incorporated information on relevant biological parameters and safety features including peak pond temperature, independent aeration and water pressure control mechanisms. Initial results indicate successful control of this biological system, and ongoing studies suggest similar mechanisms may be used for additional control objectives. In particular, this system could be used to vary pond temperatures to study biological responses and to cool ponds by addition of well water during summer months.     

Gonadotropin-releasing hormones in the African catfish: molecular forms, localization, potency and receptors

Two gonadotropin releasing hormones (GnRHs) were identified in the African catfish: chicken GnRH-II (cGnRH-II) and catfish GnRH (cfGnRH). Immunological screening of HPLC fractions from pituitary extracts indicated a third GnRH which co-eluted with lamprey GnRH-III. However, mass determination and amino acid sequencing identified this material as isotocin. This underlines the risk of identifying multiple forms of GnRH in tissue extracts on the basis of immunoreactivity in HPLC fractions. In vivo and in vitro studies demonstrated that cGnRH-II is an over 100-fold more potent gonadotropin (GTH) secretagogue than cfGnRH. This correlates with the respective receptor affinities. The presence of both GnRHs in the pituitary gland suggests that they may modulate each other's GTH release activity. Sub-threshold or low doses of cGnRH-II partly inhibited cfGnRH-induced GTH II secretion. Conversely, combinations of sub-threshold or low doses of cfGnRH with effective doses of cGnRH-II led to increases in GTH II levels similar to those induced by cGnRH-II alone. Combinations of submaximally effective dose of the 2 peptides resulted in additive effects. Hence, both GnRHs participate in the regulation of GTH II release, and their relative concentrations may determine the overall effect. Immunocytochemistry, using anti-bodies against the respective recombinant GnRH associated peptides (GAPs), as well as in situ hybridization showed that cfGnRH neurones are scattered in the ventral forebrain and project into the pituitary gland, while cGnRH-II neurones are confined to the midbrain tegmentum and without projections to the pituitary gland. Transfection experiments with GnRH receptor cDNA shows ligand activation characteristics similar to those of the native GnRH-R. Autoradiographic studies and hormone release studies indicate that GnRH-Rs in the African catfish pituitary gland are restricted to the gonadotrophs.