Mike Capra

Electrophysiological studies on ciguatera poisoning in man (Part II)

Fifteen cases of acute ciguatera poisoning were subjected to electrical studies on the sural and common peroneal nerves. Significant slowing of sensory conduction velocity and prolongation of the absolute refractory, relative refractory and supernormal periods were recorded. These findings indirectly suggest that ciguatoxin causes an abnormally prolonged sodium channel opening in nerve membranes.

Effects of ciguatoxin on nerve excitability in rats (Part I)

Ciguatera poisoning is the most common fish food poisoning encountered in man. Electrophysiological studies were performed on the ventral nerve of the tail on adult rats following intraperitoneal injection of toxic fish extract. Significant slowing of both mixed and motor nerve conduction velocities and F wave responses were recorded. Motor and mixed nerve amplitudes were significantly reduced. Both absolute and supernormal periods were significantly prolonged together with an exaggeration of the supernormal response. These findings indirectly suggest that ciguatoxin acts on mammalian nerve by prolonging sodium channel activation.

Genotype and environment: A comparative evaluation of four tilapia stocks in Fiji

Abstract The reproductive, survival and growth performance of four tilapia strains in Fiji, namely Oreochromis mossambicus (M), ‘Israel’ Oreochromis niloticus (NI), ‘Chitralada’ O. niloticus (NC) and Red tilapia hybrid (R) were evaluated in two culture environments currently used in Fiji (integrated and non-integrated farming) for three generations. Results showed significant differences among strains in all traits. Overall, the M strain had the highest breeding efficiency and average fecundity but the poorest growth rate. The NI strain showed the highest survival and a good growth rate but low breeding efficiency and fecundity. Although the R strain showed a good growth rate in favorable environments, it was prone to stress under less optimal conditions and had a relatively low survival rate and only average fecundity. The NC strain showed the best growth rate and feed conversion efficiency, relatively good breeding efficiency but average fecundity and survival. Based on a weighted performance across all traits, the NC strain was identified as the best performing strain in Fijian conditions. Significant genotype-environment interactions estimated during harvest were due to a strong rank interaction in the R strain and also magnitude interactions in the NC and NI strains. Growth performance of the M strain showed the lowest response to quality of culture environment. Future approaches to improving tilapia production in Fiji are discussed.

Juvenile growth performance among stocks and families of red claw crayfish, Cherax quadricarinatus (von Martens)

Abstract A laboratory comparison of the growth performance of juvenile red claw crayfish ( Cherax quadricarinatus ) was conducted in relation to stock and family. For stock comparison, body weight at ages during the first 84 days after release was measured for juveniles of the first generation derived from three river systems in northern Queensland, Australia: Weipa, Gilbert and Mitchell. Although the body weight of newly released juveniles was similar for the three stocks, a significant difference among stocks in body weight was shown at all post-release ages measured except at 28 days. Furthermore, the stock component of growth performance variation increased with age. On the other hand, the family component of growth variation decreased with age within all three stocks. A further study of the second generation progeny of the Gilbert River stock further demonstrated a substantial genetic component of growth performance variation in this species. Heritability estimates, based on full-sib intraclass correlations, were 0.72 ± 0.14 at 30 days, 0.48 ± 0.10 at 60 days and 0.32 ± 0.31 at 90 days after release.

Physiological responses of firefighters wearing level 3 chemical protective suits while working in controlled hot environments.

Firefighters in Queensland are exposed to hot, humid weather conditions that contribute to the overall workload encountered during emergency operations. Responding to certain hazardous material incidents requires firefighters to wear fully encapsulated chemical protective suits for a maximum period of 20 minutes. The nature of these suits, combined with workload and environmental conditions, poses a potential heat stress problem for firefighters. This study evaluates the heat-induced physiological responses of firefighters while wearing fully encapsulated chemical protective suits in a series of controlled thermal environments. Heart rate, body (aural) temperature, blood pressure, fluid loss, and a rating of perceived exertion were measured to evaluate the effect of increasing ambient air temperature during the performance of standard tasks. The results of the study indicated that the significant increase in heart rate, body temperature, and blood pressure was directly related to the increase in air temperature. The research indicates that the recommended suit wearing time of 20 minutes provided adequate physiological protection under the research conditions.

The cyanobacterium Oscillatoria erythraea—a potential source of toxin in the ciguatera food‐chain

A compound lethal to mice (i.p.) was extracted from samples of Oscillatoria erythraea, four species of mollusc and one species of molluscivorous teleost collected from the south-east coast of Queensland, Australia, during and shortly after O. erythraea blooms. The compound was chemically indistinguishable from ciguatoxin (CTX) on the basis of solvent extraction and partitioning and silicic acid chromatography. Residues derived from toxic samples elicited signs of intoxication, death and histopathological changes in mice, consistent with extracts of ciguatoxic material. Stick enzyme immunoassay tests and thin layer chromatography assessment of extracts indicated the presence of ciguatoxin-like polycyclic ether(s). O. erythraea is implicated as a potential elaborator of a CTX-like compound in the tropical marine biota.

Action of mannitol in ciguatoxin-intoxicated rats.

This study reports the effects of mannitol on nerve conduction when used as a therapeutic agent in mammals following the administration of ciguatoxin. Electrophysiological studies were performed in vivo on the rat ventral coccygeal nerve. The absolute and relative refractory periods, conduction velocity and the supernormal response were measured in rats treated with i.p. ciguatoxin, both prior to, and following, the infusion of i.v. mannitol. Ciguatoxin induced significant prolongation of the absolute refractory period as well as significant slowing of the compound nerve conduction velocity. The magnitude of the supernormal response was significantly increased and the duration of the supernormal period extended in ciguatoxin-treated animals. Recordings collected following the infusion of mannitol in these ciguatoxin-treated animals showed that mannitol did not reverse the effects of ciguatoxin on nerve conduction in any of the parameters measured.

The relative growth of chelipeds and abdomen and muscle production in male and female redclaw crayfish, Cherax quadricarinatus von Martens

Abstract The relative growth of chelipeds and abdomen and muscle production in male and female redclaw crayfish (Cherax quadricarinatus) were studied. In the sample of animals measured, a rapid increase in the relative growth of chela width and cheliped length occurred in males with a carapace length of 43 and 45 mm, respectively. Males larger than this size had wider chelae and longer chelipeds than females with a similar carapace length. A comparison of the ratio of abdomen width to carapace width points to difference in the growth pattern of the abdomen between sexes. In males with a carapace length shorter than 42 mm, the ratio increased with carapace length while it decreased in those with a carapace length longer than 42 mm. In females with a carapace length shorter than 49 mm, the ratio increased with carapace length while it was constant in those with a carapace length longer than 49 mm. Due to the compensation of muscle production from chelae in males and from abdomen in females, total muscle production in relation to carapace length was similar between sexes. However, the percentage of muscle to body weight varied with carapace length and the highest percentage (34%) occurred in the animal with a carapace length of 74 mm. The possible application of these findings is discussed in relation to the definition of sexual maturation and cropping strategy for this species.

Ciguatoxin-protein association in skeletal muscle of Spanish mackerel (Scomberomorus commersoni).

A study of soluble protein from skeletal muscle of Scomberomorus commersoni was undertaken to elucidate aspects of ciguatoxin (CTX) bioaccumulation in marine teleosts. Skeletal muscle tissue samples from toxic and non-toxic specimens were subjected to fractionation, centrifugation, (NH4)2SO4 precipitation and Sephacryl S-200 chromatography of soluble proteins. Toxicity associated with various fractions was assessed by mouse bioassay, and toxic and non-toxic soluble protein fractions were compared using SDS-PAGE. CTX eluted from Sephacryl S-200 with soluble proteins of apparent mol. wt between 35,500 and 59,500. The toxic eluate contained 1.4% of total sample protein and 15% of total sample toxicity, with an associated 7.2-fold increase in specific activity. SDS-PAGE comparisons show two protein bands in the 37,400 and 40,600 mol. wt range which appeared in toxic soluble protein fractions, but were not detectable in control (non-toxic) samples. These findings are interpreted as being consistent with the association of CTX with at least one monomeric soluble protein of 37,000 to 40,600 mol. wt from toxic S. commersoni skeletal muscle.

Cryopreservation of summer whiting (Sillago ciliata) spermatozoa

Abstract Sperm, manually stripped from male Sillago ciliata , were successfully cryopreserved in the vapour of liquid N 2 using glycerol or DMSO as the cryoprotectant. Methanol and propylene glycol had no cryoprotective effect on the summer whiting sperm. There were no significant differences in post-thaw fertility or duration of motility of the spermatozoa frozen with DMSO or glycerol and glycerol was used for further trials. The post-thaw duration of motility was improved with the addition of egg yolk to the cryoprotectant mixture. The cryoprotectant medium contained 1.25 M glycerol in fish Ringer; egg yolk was added (40% v/v ) (final concentration of 0.645 m M ) and the semen diluted 6.74, 1. Freezing was best performed in liquid nitrogen vapour with transfer and storage in liquid nitrogen; instant immersion in liquid nitrogen reduced the viability of the sperm. Storage in liquid nitrogen over a 7-day period did not significantly affect duration of motility. Equilibration prior to freezing was not necessary and sperm could be thawed at a range of temperatures from 0 ° to 40 °C without affecting their post-thaw duration of motility.