Showing papers in "Journal of Fish Biology in 1973"
TL;DR: Routine haematological methods for examining fish blood are suggested as a possible means of assessing fish health but there is a need for establishing values in health, disease and various stress conditions before their value in diagnosis can be evaluated.
Abstract: Some routine haematological methods for examining fish blood are described including haemoglobin estimation, haematocrit, erythrocyte counts, erythrocyte sedimentation rate, total and differential leukocyte counts, and cytochemical staining. Descriptions of stained blood cells are given as are the ranges and mean values for the above tests on brown trout Salmo trutta (L.). These methods are suggested as a possible means of assessing fish health but there is a need for establishing values in health, disease and various stress conditions before their value in diagnosis can be evaluated.
1,441 citations
TL;DR: The effect of food level on the egg production of three-spined sticklebacks was studied experimentally and weight at maturity was positively correlated with the number of spawnings, the mean number and the weight of eggs produced per spawning.
Abstract: The effect of food level on the egg production of three-spined sticklebacks was studied experimentally. High food levels increased the percentage of fish that matured, and the weight of the fish at maturity. Weight at maturity was positively correlated with the number of spawnings, the mean number and the weight of eggs produced per spawning. Food level had no effect on the size of the eggs, whether size was expressed as wet or dry weight per egg. Fish on the highest food level spawned at shorter intervals than fish at the lower levels. A preliminary model of the effect of food supply on recruitment to a stickleback population is nresented.
179 citations
TL;DR: It is impossible to say whether the differences that were observed between Kamloops and these other varieties were due to strain alone, since other variables were present, but some problems associated with establishing normal ranges for these parameters in fish are discussed.
Abstract: Fifty rainbow trout of the Kamloops strain were examined for 12 haematological parameters: erythrocyte sedimentation rate, haemoglobin, packed cell volume, erythrocyte count, erythrocyte diameters, mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration, leukocyte count, differential leukocyte count, plasma total protein and plasma glucose concentration. The fish had been held under known environmental and dietetic conditions, and at the time of sampling were 14 months old. The majority of results for erythrocyte sedimentation rate, haemoglobin, packed cell volume, erythrocyte count, erythrocyte diameters, total protein and differential leukocyte count fell within narrow ranges. The total leukocyte counts and glucose levels were more widely spread. The results are discussed and compared with those already published for Idaho and Shasta strains. It is impossible to say whether the differences that were observed between Kamloops and these other varieties were due to strain alone, since other variables were present. Some problems associated with establishing normal ranges for these parameters in fish are discussed.
170 citations
TL;DR: Normal recruitment to insular fisheries may be very greatly dependent upon the success of parent stocks spawning elsewhere in the Caribbean and the abundance of recruits to a particular area may be dependent on the speed and direction of the prevailing currents which carry larvae and juveniles to the insular shelves.
Abstract: Observations are recorded on the time of spawning of 83 species of Caribbean reef fishes. Details of seasonal variations in the percentage of sexually active fishes are given for 35 species. The majority of species spawn mostly when water temperatures are minimal, in February, March and April. The expected biomass of reef fish eggs in the plankton is about twelve times greater in the above mentioned period than in the period from June to December. Normal recruitment to insular fisheries may be very greatly dependent upon the success of parent stocks spawning elsewhere in the Caribbean and the abundance of recruits to a particular area may be dependent upon the speed and direction of the prevailing currents which carry larvae and juveniles to the insular shelves.
168 citations
153 citations
TL;DR: Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals.
Abstract: Effects of mixtures of chloride salts of cadmium, copper and zinc on survival, whole body residues, and histopathology of mummichog, Fundulus heteroclitus (L.), were investigated in synthetic sea water at 20‰ salinity and 20°C. Mixtures of Cu2+ and Zn2+ as indicated by 96 h bioassay studies produced more deaths than expected on the basis of toxicities of individual components. Concentrations of Cd2+ not ordinarily lethal exerted a negative effect on survival of fish intoxicated by salts of copper, zinc, or both.
Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals. Residues from survivors held in mixtures, especially Cd2+ and Zn2+ mixtures, did not conform to patterns observed for single elements. Whole body aggregates of Cd, Cu, and Zn from dead mummichogs were of limited worth owing to possible accumulation of these metals from the medium after death.
Renal and lateral line canal lesions were noted in all fish subjected to copper concentrations of 1 mg/1 and higher. Renal lesions observed in fish immersed in mixtures of Cu2+ and Cd2+ assumed a damage pattern characteristic of Cd2+; with mixtures of Cu2+ and Zn2+, lesion were typical of Cu2+-induced damage. Lesions induced in lateral line epithelium by Cu2+ were not affected by either Cd2+ or Zn2+. Epithelia lining the oral cavity were necrotized by the caustic action of high levels of Zn2+ (60 mg/1) and of Cu2+ (8 mg/1).
142 citations
TL;DR: The validity of using extruded intra-ovarian oocytes for in vivo assessment of ovarian maturity in the grey mullet was established and statistical analyses of oocyte diameters and diameter-frequency distributions data from duplicate in vivo samples removed from the same ovarian site in each of 17 females showed no significant differences.
Abstract: The validity of using extruded intra-ovarian oocytes for in vivo assessment of ovarian maturity in the grey mullet was established. The diameter of sampled, unfixed oocytes was used as a reference point for comparative purposes. Analysis of variations in oocyte diameters among samples removed from seven different ovarian locations indicated that mullet oocytes develop in synchrony and that in vivo samples taken from any area in the ovary would be representative of the entire ovary. Statistical analyses of oocyte diameters and diameter-frequency distributions data from duplicate in vivo samples removed from the same ovarian site in each of 17 females showed no significant differences and validated the accuracy of the method. Similar comparisons of data from in vivo and in vitro samples revealed no statistically significant differences.
108 citations
TL;DR: Evidence of a long-standing host-parasite relationship which has evolved to an advanced state of adaptation on the part of the parasite and tolerance on thePart of the host is shown.
Abstract: Eighty-nine O-group plaice from a natural population were exposed at 15°C to heavy infection by Cryptocotyle lingua cercariae. Subsequently 45 fish were retained at 15°C, whilst 44 were held at 5°C. Both groups were sampled by killing individual fish at intervals of 6,18,42 h and daily thereafter up to 710 h. Entire fish were fixed immediately in formol saline, transversely sectioned and stained by H & E, PAS, PAS-diastase, JSDB 109, Picro-Mallory, Masson's trichrome, Gram-Weigert and Alcian blue. Histopathological observations showed: (a) epidermal lesions associated with encysted metacercariae in adjacent tissues; (b) myofibrillar necrosis associated with bacteria possibly introduced by the parasite; and (c) a reactive swelling of the intermuscular septa. The progressive development of the parasite cyst and host capsule is described. Development of both was markedly inhibited at the lower temperature, but the inflammatory response at either temperature was slight. This may be evidence of a long-standing host-parasite relationship which has evolved to an advanced state of adaptation on the part of the parasite and tolerance on the part of the host.
105 citations
TL;DR: Conditioned populations showed a high degree of discriminatory ability towards a trigger that supplies food and one that does not, and the choice system was used to examine preferences for the taste of pelleted foods.
Abstract: A system for the quantitative study of the learning capacity of rainbow trout and its application to the study of food preferences and of behaviour. Groups of trout were self-trained in about 10 days to actuate a trigger and feed themselves. This capacity was retained for 3 months without the stimulus of continuous reinforcement. Presented with a choice, conditioned populations showed a high degree of discriminatory ability towards a trigger that supplies food and one that does not. The choice system was used to examine preferences for the taste of pelleted foods. A trained population, under continuous illumination developed a feeding rhythm that occurred about every 8 h.
103 citations
TL;DR: Throughout the last year of larval life, the animal stored a greater proportion of lipid, presumably to facilitate the energy demands of metamorphosis during which this food store underwent a marked reduction.
Abstract: Estimates were made of the growth rates and proximate body composition of larval and metamorphosing P. marinus (L.) collected at various times of the year from Shelter Valley Creek, Lake Ontario. Analysis of length-frequency data indicates that the average duration of larval life was 6 years, with metamorphosis occurring predominantly in the length range above 13 cm. Increases in length were almost entirely restricted to the warmest months and did not take place during the final year of larval life. Three categories were thus recognized for the proximate analysis: ammocoetes 13 cm and metamorphosing individuals. In ammocoetes <13 cm, seasonal differences were observed in the regression coefficients in the logarithmic relationships between wet weight and length and between each of water, lipid and ash and the wet weight. No such difference was found for the regressions between protein and wet weight. For a fixed length (9 cm), the wet weight varied only slightly during the year, although a small peak was seen in May. When considered on the basis of fixed weight (1 g), the relative amount of lipid deposited was greatest in May/July, coincident with a high diatom density. The water content followed an inverse pattern to that of lipid, while the protein and ash contents showed little seasonal variation and exhibited values lower than those normally found in teleosts. Throughout the last year of larval life, the animal stored a greater proportion of lipid, presumably to facilitate the energy demands of metamorphosis during which this food store underwent a marked reduction.
102 citations
TL;DR: Changes in leukocyte counts in mirror carp infected with Ichthyophthirius multifiliis were recorded during the disease and a significant shift towards younger cell populations was evident among the neutrophils.
Abstract: Changes in leukocyte counts in mirror carp infected with Ichthyophthirius multifiliis were recorded during the disease. Leukocytes were classified according to their appearance and stage of development. The overall white blood cell count in infected carp remained within the range found in normal carp under similar conditions. The first recognizable event in leukocyte dynamics was a sharp but temporary drop in lymphocytes with a concurrent rise in neutrophil percentages early in the infection. A similar trend also appeared towards the end of the infection. A significant shift towards younger cell populations was evident among the neutrophils. Blast cells with morphological characteristics of neutrophils appear in the circulation. The percentage of these cells and of other blast cells rose progressively during the infection. The number of cells termed fine reticular cells, also rose during infection. White blood cell changes in the mirror carp infected with I. multifiliis were similar to changes observed for other diseases and also in response to certain stress conditions.
TL;DR: The food of 26 common fish species of the Lagos lagoon are given and it is shown that the food of the species covers a wide spectrum and most of the available invertebrates are being utilized as food by the fishes.
Abstract: The food of 26 common fish species of the Lagos lagoon are given. It is shown that the food of the species covers a wide spectrum and most of the available invertebrates are being utilized as food by the fishes. The intra and interspecific relationship of the food and feeding habits of the various species are discussed.
TL;DR: Two critical periods associated with high larval mortality were apparent on the 2nd–3rd and 8th–11th days after hatching, preceded by an increase in specific gravity of larvae followed by passive sinking to the bottom of the rearing tank.
Abstract: Larvae from artificially bred grey mullet were reared in the laboratory and survival rates of 0.2 %, 5 % and 5 % achieved in three of six trials. Food consisted of wild zooplankton and Anemia nauplii. Feeding began on the fifth day, when the yolk sac was depleted, and intensified on the ninth day. The rate of yolk absorption and feeding intensity were reflected in the growth curve. Larval survival was not affected by withholding food from the larvae till the seventh day from hatching. Two critical periods associated with high larval mortality were apparent on the 2nd–3rd and 8th–11th days after hatching. These were preceded by an increase in specific gravity of larvae followed by passive sinking to the bottom of the rearing tank. Larval length increased from 2.63 mm at hatching to 17.69 mm at the end of the 42-day larval period. The larvae survived on benthic diatoms therefter. Maximum survival rates were achieved at 22°C. (Oceanic Institute Contribution No. 101).
TL;DR: Specific studies of this species involved the elucidation and evaluation of abiotic effects on local upstream migrations and preliminary age and growth estimations, which indicated that upstream movements appeared to be affected by water temperature and moon phase.
Abstract: General studies cover the habitat and life cycle of a migratory population of Prochilodus platensis. Specific studies of this species involved the elucidation and evaluation of abiotic effects on local upstream migrations and preliminary age and growth estimations. Upstream movements appeared to be affected by water temperature and moon phase. Most of the fish moved upstream when the temperature was between about 14 and 18°C at the particular monitoring point. Catches of ascending fish were highest during the full moon quarter, less during the waxing phase and least during the waning and new moon quarters. Length frequency and scale check data allowed approximate, indirect estimations to be made of the modal lengths attained in each of the first five age-groups.
TL;DR: Many acutely poisoned fish recovered in zinc-free hard water, regeneration of epithelia being accompanied by a temporary appearance of chloride cells on the secondary lamellae as well as the formation of membrane-bounded vesicles and dense accumulations of metabolites.
Abstract: Concentrations of 0.5–1.0 mg Zn2+/dm3 distilled water killed sticklebacks after 1–3 days, producing detachment and sloughing of epithelial cells, and coalescing of adjacent secondary lamellar epithelia. Cytoplasmic abnormalities included extensive vacuolation, followed by swelling of nuclei and mitochondria leading to cellular disintegration. Many acutely poisoned fish recovered in zinc-free hard water, regeneration of epithelia being accompanied by a temporary appearance of chloride cells on the secondary lamellae. Concentrations of 2.0–6.0 mg Zn2+/dm3 hard water were not toxic over periods of up to 700 h. Extensive cytoplasmic abnormalities appeared, however, including the formation of membrane-bounded vesicles and dense accumulations of metabolites. The most pronounced effect was the appearance of active chloride cells on the secondary lamellae. The possible involvement of chroride cells in the excretion of ions other than chloride is briefly discussed.
TL;DR: Biochemical measurements have been made on the red and white myotomal muscles and liver of fish subjected to both varying intensities of sustained swimming and short periods of vigorous swimming, and free creatine was found to increase only during high speed swimming in the white muscle.
Abstract: A study has been made of the maximum sustained swimming speed of Crucian carp Carassius carassius (L.) using a fixed velocity technique. The data obtained from swimming tests on 214 carp have been analysed using the method of probit analysis. The 50% fatigue level for 13–16 cm fish acclimated to 9.5±0.6°C has been estimated to be 3.35 lengths/sec. Biochemical measurements have been made on the red and white myotomal muscles and liver of fish subjected to both varying intensities of sustained swimming and short periods of vigorous swimming. Free creatine was found to increase only during high speed swimming in the white muscle. Elevated lactate concentrations occurred at both low and high sustained swimming speeds in the red superficial muscle but not during short periods of strenuous exercise. Glycogen depletion from the red musculature also only took place at the sustained swimming speeds investigated. The reverse situation was operative in the white muscle, significant glycogen depletion occurring only at the highest swimming speed studied. Lactate levels were only significantly different from non-exercised fish in the fish swimming at the higher velocities. The effects of periods of recovery following 200 min of sustained swimming were also investigated. White muscle lactate was at a higher level than non-exercise fish 5 h post-exercise, while both red muscle glycogen and lactate rapidly returned to pre-exercise concentrations. Biochemical measurements on the myotomal muscle types have been discussed in relation to the swimming performance of the fish and the division of labour between red and white fibres.
TL;DR: The cold-adapted population was less tolerant of heat and more tolerant of cold as would be anticipated and non-genetic scope for adaptation as related to changes in the thermal history of the individual and expressed in terms of the tolerance domain was identical for both populations.
Abstract: The capacity of a warm-adapted population of mosquito fish (Gambusia affinis) from the Sonoran Desert and a cold-adapted population from northern Utah to adjust to changing environmental temperatures has been described in terms of four criteria: (1) critical thermal maxima, (2) resistance times at high, lethal temperatures, (3) upper incipient lethal temperatures, and (4) lower lethal temperatures. Non-genetic scope for adaptation as related to changes in the thermal history of the individual and expressed in terms of the tolerance domain was identical for both populations. Genetic differences in adaptive capacity were apparent. The cold-adapted population was less tolerant of heat and more tolerant of cold as would be anticipated.
TL;DR: The efficacy of fractionated salmon pituitary gonadotropin as a spawning agent in Mugil cephalus L. was tested and ‘priming’ effect was observed following the initial injection and is discussed.
Abstract: The efficacy of fractionated salmon pituitary gonadotropin as a spawning agent in Mugil cephalus L. was tested. Natural spawning was induced in all females with a total dose of 11.9–20.9 μg/g body wt. Spawning dose varied inversely with initial mean egg diameters of recipient females. A ‘critical’ mean egg diameter of 650–700 μ was observed to precede the hormone dose that induced spawning. A ‘priming’ effect was observed following the initial injection and is discussed. The ‘latency period’ was determined to be 10–15 h; fecundity was estimated at 648 eggs/g body wt. Courtship, spawning and fertilization occurred naturally with uninjected males.
TL;DR: The tagging lesion provides a very suitable model for the study of short and long term inflammation in salmonids and studies on the modification of these defensive mechanisms by temperature.
Abstract: Histopathological studies were carried out on the pathogenesis of the lesion induced by the insertion of a light plastic identification tag, in salmon parr on the river North Esk, Scotland. The experiments were carried out at mean water temperature of 127deg;C, 8°C and 4°C. The inflammatory response was similar at each temperature, but the rate of its development was markedly inhibited at 4°C. The qualitative response at the lower temperature was also slightly different in that polymorphonuclear leukocytes appeared to play a slightly more dominant role and the connective tissue response, which in all cases outweighed myofibrillar regeneration was more cellular at that temperature. The tagging lesion provides a very suitable model for the study of short and long term inflammation in salmonids and studies on the modification of these defensive mechanisms by temperature.
TL;DR: Variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.
Abstract: The number of eggs spawned by female three-spined sticklebacks Gasterosteus aculeatus (L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.
TL;DR: Mirror carp infected with Ichthyophthirius multifiliis (Fouquet) under standardized conditions recorded the size and number of parasites at selected sites on the body during the course of the infection, which resulted in 100% mortality between 22–25 days.
Abstract: Mirror carp were infected with Ichthyophthirius multifiliis (Fouquet) under standardized conditions. The size and number of parasites at selected sites on the body were recorded during the course of the infection. Initial exposure to 40 mature parasites resulted in a mild infection with 100% recovery after 18 days. Recovered fish did not appear to be carriers of the parasite. Exposure to 400 parasites resulted in 100% mortality between 22–25 days. The growth rate of the parasite was linear. Parasites were more numerous in the dorsal surface of the fish than in the lateral or ventral surface. The increase in parasite numbers during the disease was greater in the gills than in the skin.
TL;DR: Aspects of the reproductive biology of the sprat in inshore waters of the west coast of Scotland were investigated from August 1970 to July 1972, finding it significantly correlated to weight, length and age.
Abstract: Aspects of the reproductive biology of the sprat in inshore waters of the west coast of Scotland were investigated from August 1970 to July 1972. Spawning in sprat lasts for a period of five to six months, starting in February-March. Minimum size of maturity is 88–90 mm in both sexes but males tend to mature earlier in the season. Sprat shed their eggs in 7–10 batches. There is generally a higher proportion of females in the population. The fecundity ranges from 8700 to 46,600 in fish between 95 and 146 mm in length. It is significantly correlated to weight, length and age.
TL;DR: Growth was fast in the spring and summer, slowing during the late autumn and winter, and abundance during the period September 1967 to May 1968 decreased at an average rate of 25% of the sampled population per month.
Abstract: The ecology of 0- and 1-group turbot was studied at Borth, Cardiganshire, during the years 1966–68. Newly-metamorphosed turbot appeared in the surf zone from July to October, Abundance during the period September 1967 to May 1968 decreased at an average rate of 25% of the sampled population per month. Fish of the 1966 year-class grew from a mean length of 4.5 cm in September 1966 to 14.4 cm in October 1967. Growth was fast in the spring and summer, slowing during the late autumn and winter. The most important food items of 0- and 1-group turbot by percentage occurrence and dry weight were polychaetes and mysids. The daily food intake of 0-group turbot in September 1967 was estimated as 2.5 % of the body weight per day.
TL;DR: A method is described for distinguishing the scales of sea trout from brown trout by their strontium content, which shows clear differences between those of brown trout and sea trout.
Abstract: A method is described for distinguishing the scales of sea trout from brown trout by their strontium content. Scales of brown trout contain less than 200 μgSr/g and those of sea trout more than 300 μgSr/g.
TL;DR: Temperature and salinity tolerances of juvenile Rhabdosargus holubi (Steindachner) were determined experimentally and indicated that they are tolerant over a wide range of salinities and temperatures and that little interaction between temperature andsalinity occurs.
Abstract: Temperature and salinity tolerances of juvenile Rhabdosargus holubi (Steindachner) were determined experimentally. Results indicated that they are tolerant over a wide range of salinities (0.7–70‰) and temperatures (10–30°C) and that little interaction between temperature and salinity occurs. R. holubi is restricted to the warm temperate waters of southeastern Africa. It is absent from the subtropical Indian Ocean and from temperate Atlantic Ocean waters. The juveniles occur mainly in the inshore waters and estuaries. Evidence from tolerance experiments and salinity and temperature data from southern African estuaries suggested that the distribution of R. holubi is controlled by temperature.
TL;DR: This, the first of two papers on the scarcer freshwater fishes of the British Isles, gives an account of the introduced species and a brief discussion on the introduction of exotic fishes to aquatic ecosystems follows.
Abstract: This, the first of two papers on the scarcer freshwater fishes of the British Isles, gives an account of the introduced species. Nineteen species are included. The natural distribution of these fishes, the history of their introduction, their success in acclimatization, and their present distribution in the British Isles are given. A brief discussion on the introduction of exotic fishes to aquatic ecosystems follows.
TL;DR: The HCG, FSH/LH combination, Synahorin+mullet pituitary homogenate, and partially purified salmon gonadotropin were equally effective, at the doses used, in inducing oocyte maturation and preventing onset of atrophy before completion of vitellogenesis.
Abstract: The effects of mammalian gonadotropins, methyltestosterone and partially purified salmon gonadotropin on spermiation and oocyte maturation were studied in adult grey mullet. Methyltestosterone was a potent spermiating agent in both prespawning and spawning trials. The most effective dose was 5 mg/100 g body weight. Human chorionic gonadotropin (HCG) was moderately effective at a dose rate of 20 IU/100 g body weight. Both hormones blocked resorption of milt in captive animals. The HCG, FSH/LH combination, Synahorin+mullet pituitary homogenate, and partially purified salmon gonadotropin were equally effective, at the doses used, in inducing oocyte maturation and preventing onset of atrophy before completion of vitellogenesis. Atrophy occurred in all experimental fish at mean oocyte diameter of 750 μ. The significance of this finding is discussed. (Oceanic Institute Contribution No. 98).
TL;DR: Results suggest that whiting to the east of the Isle of Man form a separate sub-stock from those to the west of the island, and Experimental evidence suggests that the lower salinity of Morecambe Bay may be responsible for the lower infestation of whiting by Diclidophora which appeared to be unaffected by a lowered salinity.
Abstract: Infestation of whiting with the helminths Derogenes varicus Muller, Hemiurus communis Odhner, Grillotia erinaceus Van Beneden (plerocercoids) and Contracaecum clavatum Rudolphi, and the copepod Lernaeocera branchialis L., increased with the age of the fish but infestation with the helminths Lecithaster gibbosus Rudolphi, Stephanostomum pristis Looss and Podocotyleatomon and the copepod Clavella uncinata Muller decreased as the fish aged. Infestation with the gill monogenean Diclidophora merlangi Kuhn remained at much the same level in fish 1–5+ years old. Derogenes, Hemiurus, Lecithaster, Cotracaecum and Stephanostomum showed seasonal fluctuations in the levels of their populations in whiting. In all cases the parasites reached a main peak in the summer and early autumn, a time when juvenile digeneans were most apparent.
Whiting from Morecambe Bay were less infested with Clavella than whiting taken from other areas. Experimental evidence suggests that the lower salinity of Morecambe Bay may be responsible; however, this could not account for the lower infestation of Morecambe Bay whiting by Diclidophora which appeared to be unaffected by a lowered salinity. Whiting from the east side of the Isle of Man were more infested with Lernaeocera but less infested with Diclidophora than fish from the west side of the island. The myxosporidian Myxobolus aeglefini Auerbach was externally visible in the sclera of whiting from the east side of the island but absent from the sclera of whiting from the west side of the island. It is, therefore, suggested that whiting to the east of the Isle of Man form a separate sub-stock from those to the west of the island.