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.     

Culture environment and the odorous volatile compounds present in pond-raised channel catfish (<Emphasis Type="Italic">Ictalurus punctatus</Emphasis>)

A headspace solid-phase micro-extraction (SPME) coupled with GS-MS method was used to measure volatile compounds in fillets from musty off-flavor, muddy off-flavor, and on-flavor channel catfish (Ictalurus punctatus), along with water and soil samples from the farm ponds in which the fish had been raised. Two ponds of each type of flavor were selected, and five fish, water, and soil samples were collected from each pond. Linear and multiple linear regression analyses were carried out between/among off-flavor strength and volatile compound contents to investigate their possible correlations. The combination of two strong off-flavor compounds, 2-methylisoborneol (MIB) and geosmin (GSM), was probably mainly responsible for the musty off-flavor in the catfish fillets, and an odorous alcohol, 1-hexanol, was correlated with muddy off-flavor (p =?0.015). There was a strong correlation between beta-cyclocitral and MIB in a pond that gave musty off-flavor catfish contents (p =?0.006), suggesting that these compounds might be generated by similar cyanobacteria. The contents of GSM, MIB, and beta-cyclocitral were high in the water of ponds that yielded off-flavor fish, indicating that catfish might acquire these compounds from pond water.     

Development of phytoplankton communities and common off-flavors in a biofloc technology system used for the culture of channel catfish (Ictalurus punctatus)

The use of biofloc technology production systems continues to increase in the aquaculture industry worldwide. Recent research demonstrated that outdoor biofloc systems can be used to produce high yields of channel catfish (Ictalurus punctatus). However, studies have not yet been performed to determine the development and composition of phytoplankton communities and related off-flavor problems in these biofloc production systems. In this study, water samples were collected biweekly from May to November and channel catfish samples were collected during harvest in November from nine 18.6 m² biofloc culture tanks. Water and fillet samples were analyzed for levels of the common off-flavor compounds geosmin and 2-methylisoborneol (MIB). The development and composition of phytoplankton communities in each culture tank was also monitored. In addition, water and biofloc samples were evaluated to assess the microbial sources of geosmin and MIB within the culture tanks. Phytoplankton (including algae and cyanobacteria attached to bioflocs) biomass, as determined by concentrations of chlorophyll a in the water, gradually increased in all tanks over time. Phytoplankton communities that developed in the culture tanks were dominated by fast-growing, unicellular and small colonial types of green algae (chlorophytes) and diatoms (bacillariophytes) and slower growing, small colonial types of cyanobacteria (cyanophytes). A positive correlation (p < 0.05) between cumulative feed addition and chlorophyll a concentration was found. Although geosmin and MIB were present in the culture water of each tank during most of the study, levels were typically low and only one tank yielded catfish with geosmin and MIB in their flesh at levels high enough to be designated as off-flavor. A positive correlation (p < 0.05) between cumulative feed addition and MIB concentrations in the water of culture tanks indicates a greater potential for MIB-related off-flavor problems at high feed application rates. The microbial sources responsible for production of geosmin and MIB in the culture tanks remain unknown.     

Feeding behavior under dark conditions in larvae of sutchi catfish <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>

Sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature sensory organs; however, sensory organs develop rapidly with larval growth. Two-day-old larvae commenced ingesting Artemia nauplii. The larvae displayed many taste buds on the barbels, the head surface, and in the buccal cavity. Other sense organs were also well developed at this stage. Feeding experiments revealed that 2-day-old larvae ingested Artemia under both light and dark conditions, moreover, the larvae could ingest frozen dead Artemia. The ingestion rates for 4- and 7-day-old larvae were significantly higher under dark conditions than under light conditions. The rates using frozen dead Artemia were mostly higher than the rates using live Artemia. Therefore, feeding behavior under dark conditions is most likely not mediated by visual or mechanical senses, but rather by chemosensory senses, such as taste buds. Larval fish are vulnerable to predators; thus, if they can search for and eat food at night, they can avoid diurnal predators. The behavior observed here appears to represent their survival strategy. Moreover, these results suggest a new possibility that sutchi catfish larvae can be reared under dark or dim light conditions in order to improve survival and growth rates as in the case of African catfish Clarias gariepinus.     

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.     

Largemouth bass predators reduce growth,feeding and movement in juvenile channel catfish

Fine ML, Mayo MS, Newton SH, Sismour EN. Largemouth bass predators reduce growth, feeding and movement in juvenile channel catfish. Ecology of Freshwater Fish 2011: 20: 114–119. © 2010 John Wiley & Sons A/S Abstract – Animals utilise sensory cues to make decisions that will decrease their vulnerability to predation. With a well‐developed olfactory system and taste buds located inside the mouth and on the external body surface, catfishes are excellent subjects to investigate nonconsumptive predator effects. Juvenile channel catfish Ictalurus punctatus are often eaten by largemouth bass Micropterus salmoides, and we tested the hypothesis that largemouth bass fed catfish would adversely affect foraging and growth in channel catfish. Groups of catfish were placed in tanks partitioned by a mesh screen: experimental tanks had a largemouth bass on the other half of the tank, and control tanks had an empty chamber. Experimental catfish exhibited a long‐term decrease in spontaneous motion, feeding and growth. Feeding catfish to the bass caused the experimental catfish to freeze after a multi‐second latency suggesting transport of an alarm cue. Thus, there were long‐term effects from the continuous presence of the bass and additional short‐term cues from the bass consuming a catfish.     

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.     

Current status of farming practices of striped catfish, Pangasianodon hypophthalmus in the Mekong Delta, Vietnam

Aquaculture of catfish, Pangasianodon hypophthalmus (Sauvage), locally known as “ca tra”, and commonly referred to as striped catfish, river catfish and sutchi catfish, in Vietnam, having recorded a production of 683,000 tonnes in 2007, valued at about 645 million US$ is one of the largest single species based farming system, restricted to a small geographical area, in the world. The product is almost totally exported to over 100 countries as frozen fillets, as an acceptable alternative to white fish. Catfish is farmed mostly in earthen ponds, up to 4 m deep, in nine provinces in the Mekong Delta in South Vietnam. The results of the grow-out system of catfish farming in the Mekong Delta from a survey of 89 farms are presented. The farm size ranged from 0.2 to 30 ha with a mean of 4.09 ha. The frequency distribution of the yield in tonne/ha/crop and tonne/ML/crop corresponded to a normal distribution curve, where 75% of the farms yielded 300 tonnes/ha/crop or more. It was found that the yield per crop was significantly correlated (p < 0.05) to stocking density, pond depth and volume but not to pond surface area. Yields per crop was significantly different (p < 0.05) between upper and lower provinces of the Mekong Delta and water source (river versus channels), amongst others. It was evident that diseases and/or symptoms were observed to occur mostly in accordance with the onset of rains. In this paper the history of the catfish farming in the Mekong Delta is briefly traced, and current harvesting and marketing procedures as well as pertinent social elements of the farming community are dealt with.     

Development of sensory organs and changes of behavior in larvae of the sutchi catfish, <Emphasis Type="Italic">Pangasianodon hypophthalmus</Emphasis>

Larvae of the sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature features, but sensory organs develop rapidly as the fish grow. By 1 day old, yolk-sac larvae showed notochord flexion, and by 2 days old larvae were observed to have consumed a large part of the yolk sac. At this stage, larvae had well-developed eyes, olfactory organs with ciliated receptor cells, inner ears with semicircular canals, and numerous taste buds, and they commenced ingestion of rotifers, Artemia nauplii, and artificial compound feed. Two-day-old larvae had many free neuromasts on the surface of the head and flanks and clearly showed rheotaxis. By 20 days old, free neuromasts in postflexion larvae had sunk under the skin. At this later stage, larvae swam against a water current and schooled along the side of the fish tank. Rapid development of sensory organs and notochord flexion would be an adaptation for survival in conditions of flowing water, as in the Mekong River. In this study, we show that development of the lateral line in the postflexion stage seems to be closely related to larval behavior, suggesting that these developments could be essential for sutchi catfish larvae survival.     

Physiology Approaches to the Management of Off-Flavors in Farm-Raised Channel Catfish,Ictalurus punctatus

To obtain optimal yields of channel catfish, Ictalurus punctatus, large quantities of feed are added to ponds. Nutrients released from feed support dense algal and bacterial populations. Although some microbes produce oxygen and remove wastes, certain taxa produce the muddy/earthy off-flavor metabolites, 2-methylisoborneol (1-R-exo-1, 2, 7, 7-tetramethyl-bicyclo-[2, 2, 1]-heptan-2-ol) (MIB) and geosmin (1α, 10β-dimethyl-9α-decalol). Currently, off-flavors are one of the biggest problems affecting the channel catfish industry. Fish exposed to water containing either geosmin or MIB rapidly concentrations of these compounds in their tissues. Conversely, fish placed in water free of off-flavor metabolites exhibited markedly reduced concentrations of MIB after 8 hours and continued to improve in flavor quality throughout 24 hours, indicating a progressive purging or clearing of off-flavor compounds from their tissues. Relatively lean (< 2.5% fat) fish lost MIB more rapidly than fish with greater fat contents (> 2.5% fat). This paper proposes that aquaculture production systems should be managed for maximum production efficiency and yields, and that fish containing off-flavors then could be purged in special facilities. Purging systems that rely on a constant flow require large amounts of water and may not be widely practical. Systems that recirculate water may be more feasible. However, biological filters and other components of recirculating systems may become sources of off-flavors. The early detection of off-flavor-producing taxa and the competitive exclusion of problematic populations may be useful in preventing off-flavor production in recirculating purging systems.