Histopathology and prevalence of epidermal papillomas epidemic in brown bullhead, Ictalurus nebulosus (Lesueur), and white sucker, Catostomus commersoni (Lacépède), populations from Ontario, Canada

Abstract. White sucker, Catostomus commersoni (Lacépède), and brown bullhead, Ictalurus nebulosus (Lesueur), populations throughout the Great Lakes examined for evidence of pollution associated neoplasia exhibited a variety of morphologically distinct skin lesions. Three types of skin lesions affected white suckers: (a) focal on the lips, (b) discrete on the body, or (c) raised mucoid focal lesions on the skin and fins. Histologically, all three types featured a continuum between mild epidermal hyperplasia and benign papillomata. Brown bullheads exhibited a single variably shaped raised lesion on all body surfaces and within the oral cavity in addition to focal lip lesions. All bullhead lesions exhibited a continuum between mild epithelial hyperplasia and papillomata. Some skin lesions in both species were invasive but most abnormalities represented some stage in the development of epidermal papillomas. These papillomas superficially resemble papillomas common in many fish species and which are associated with viruses, but sucker and bullhead papillomas exhibit a unique range of histopathological and gross morphological appearances. The high prevalence of these papillomas, affecting up to 60% of some populations in polluted areas, supports the possibility that carcinogenic chemicals in the sediments are influencing papilloma development.     

Comparative Annulus Formation on Anatomical Structures of the White Sucker, Catostomus commersoni (Lacépède)

Of 32 structures examined in the white sucker, annulus formation is potentially suited for age determination only on the dermethoid, frontal, lacrimal and rib bones, pectoral fin rays and body scales. Ages assigned by annulus counts on each of the above-noted structures, except scales, were in total agreement. Scale annulus counts were accurate determinants of age in slow-growing riverine stocks, but not in faster-growing lake fish using the same river for reproduction. A linear correlation (r=+0.978) between pectoral fin ray radii and standard length regardless of growth rate, and confirmed by tag-recovery data, permits the accurate back-calculation of white sucker growth using annuli formed on this structure.     

Physical activity and behavior of a centrarchid fish, Micropterus salmoides (Lacépède), during spawning

Abstract – The spawning behavior of male and female largemouth bass Micropterus salmoides (Lacépède) was studied in central Illinois during the spring of 1998 to examine patterns of muscular activity associated with different spawning related behaviors and to evaluate whether electromyogram (EMG i ) telemetry could be used to detect spawning activity. Fish were implanted with EMG i transmitters (8 females, 16 males) on April 7, prior to the initiation of spawning, and were released in four 0.10-ha earthen research ponds. Continuous EMG i records, underwater videography and additional visual observations for one pair of EMG i tagged fish were collected throughout the entire spawning event, allowing us to quantify behavioral correlates of physical activity. Male EMG i activity patterns were only correlated with female patterns during courting and periods of male aggression toward the female. Overall, EMG i activity was highest for the female during shuddering (gamete deposition), whereas male EMG i activity was similarly high during periods of nest excavation, shuddering and post-spawn parental care activities. During spawning, female EMG i activity was positively correlated to shuddering. Average daily EMG i activities for females peaked on the day of spawning. As a result of their engagement in parental care activities, male activity continued to rise even after spawning was completed. EMG i telemetry appears to be a useful technique for monitoring the reproductive activity of largemouth bass, especially in areas of high cover or turbid water or during low light conditions. This technology permitted us to quantify and contrast the activity patterns associated with different spawning related activities, information that will be required to construct accurate, gender-specific bioenergetics models for this species.     

Observations on the intestinal pathology caused by three caryophyllid tapeworms of the white sucker Catostomus commersoni Laécpéde

Abstract. The structure of the parasite-host interface at the site of attachment was studied for Glaridacris catostomi, G. laruei and Hunterella nodulosa , caryophyllid tapeworms of the white sucker Catostomus commersoni . Light microscope observation of fish infected with H. nodulosa showed a loss of intestinal epithelium and lamina propria, and a chronic inflammatory response characterized by infiltration of lymphocytes and extensive hyperplasia of the submucosal tissue; intestinal pathology associated with G. catostomi and G. laruei was minimal. Electron microscope examination of the parasite-host interface revealed that in no case does parasite tissue come into direct contact with host tissue. H. nodulosa is separated from host tissue by an amorphous layer of electron lucent material (the 'eosinophilic matrix' seen with the light microscope) which appears to act as an adhesive; this material is a secretory product of the scolex glands. In G. catostomi and G. laruei a layer of material separating parasite from host tissue was also found, but it is not clear whether this layer is adhesive or protective.     

Delayed ovarian development and reduced serum steroid levels in female largemouth bass, Micropterus salmoides Lacépède, raised on pelleted feed

Female largemouth bass, Micropterus salmoides Lacépède, were raised on pelleted feed or a forage diet consisting of goldfish, Carassius auratus (L.). At the start of the present study, forage-fed bass were significantly smaller than pellet-fed bass. Forage-fed bass exhibited a significant increase in body weight, but not length, during the first month of the study; no further increases were seen in subsequent months. Pellet-fed bass did not grow significantly during the course of the study. In forage-fed bass, the gonadosomatic index (GSI) reached maximum levels in March; pellet-fed bass exhibited delayed ovarian recrudescence, reaching peak GSI approximately 4 weeks later than the forage-fed bass. There was no significant difference in the maximum GSI obtained in the two groups of fish. Serum levels of testosterone and oestradiol-17β reflected the pattern of GSI in both groups. Delayed ovarian recrudescence and suppressed serum steroid levels in pellet-fed bass might result from negative feedback effects of elevated levels of steroids found in the pelleted feed. These effects appear to be transient since pellet-fed bass resume ovarian development despite continuing to receive high steroid levels in their feed.     

Ontogeny of the digestive tract of larval percula clownfish, Amphiprion percula (Lacépède 1802): a histological perspective

An understanding of the development of the digestive system of marine fish larvae is of critical importance in determining optimal feeding regimes for their culture. The present study provides information on the histomorphological development of the digestive system of clown fish, Amphiprion percula , larvae during the first month of life. Before hatching, clownfish larvae possess an alimentary tract, liver and pancreas with absorptive and digestive capabilities. The yolk sac is completely consumed within 5–7 days at 25 °C. Clownfish larvae readily accept rotifers after hatching and a complete dietary shift from rotifer to Artemia can be accomplished at 10 days after hatch (DAH). Gastric glands in the stomach first develop 11 DAH and proliferate by 15 DAH. Both non-staining vacuoles (NSV) and supranuclear inclusion vesicles (SIV) appear at 11 DAH in the midgut and hindgut respectively. Pinocytosis and extracellular digestion coexist for about 2 weeks after hatching. While SIV disappeared completely at 25 DAH, NSV continued to be a prominent feature of the midgut during the first month.     

Temperature preference and oxygen consumption of the largemouth bass Micropterus salmoides (Lacépède) acclimated to different temperatures

The behavioural and metabolic responses of the largemouth bass Micropterus salmoides (Lacépède) to temperature were determined to define optimal thermal conditions. The final preferendum of largemouth bass juveniles determined with acute and gravitation methods was independent of the method (29.0–28.1 °C). The displacement velocity in the horizontal thermal gradient of bass juveniles was 22.4 cm h⁻¹ in the light phase and 22.6 cm h⁻¹ in the dark phase. Oxygen consumption rates in the largemouth bass increased significantly (P<0.05) from 48.8 to 69.4 mg O₂ Kg⁻¹ h⁻¹ with an increase in the acclimation temperature from 20 to 33 °C. The temperature quotient (Q₁₀) in the juveniles was 1.37–2.00 in the range of acclimation temperatures of 26–29 and 29–32 °C. The optimum temperature range for growth calculated using Jobling's equation was 28.1–28.6 °C and for Q₁₀ values 26–29 °C. The results are discussed in relation to the use of this information in aquaculture.     

Gill pathology caused by infestations of adult and preadult Dissonus manteri Kabata (Copepoda: Dissonidae) on coral trout, Plectropomus leopardus (Lacépède), (Serranidae)

Adult and preadult Dissonus manteri attached to the gills of Plectropomus leopardus cause significant pathology in the form of large hyperplastic nodules on the afferent (leading) edges of gill filaments. Nodules result from the dual actions of parasite attachment and feeding. The host response is characterized by severe epithelial hyperplasia, supplemented by fibroplasia and inflammation. Parasites attach close to the gill arch near the base of filaments. They have little effect on gill vasculature as the maxillipeds penetrate the filament superficial to the efferent filament artery and do not interfere with the blood vessels of the secondary lamellae. Tissue proliferation is limited to the wide portion of filament 'edge' epithelium in the proximal third and also does not extend to the secondary lamellae. Nodules are most numerous towards the ends of hemibranchs and are generally absent from the central regions. Leading hemibranchs bear significantly more nodules than their trailing counterparts. Of the total number of nodules, 20.5% are located on the pseudobranchs. Distribution patterns are considered to be primarily the result of D. manteri avoiding strong water currents, although this cannot explain the difference between numbers on leading and trailing hemibranchs.     

Diel and seasonal changes in nutritional condition of the anadromous twaite shad Alosa fallax fallax (Lacépède, 1803) larvae

Abstract –  In this work we aim to study: (i) the diel and seasonal changes in nutritional condition, herein RNA/DNA ratios, of twaite shad ( Alosa fallax fallax ) larvae and (ii) the influence of environmental and biological covariates on those changes. Samples were collected in the River Mira (Portugal) from February 1998 to July 2000. The RNA/DNA ratios were significantly lower than average during dawn and dusk hours. This pattern can be attributed to: the absence of better-fit specimens escaping the net; a nightly increase in the RNA content in response to circadian rhythm; and/or nucleic acids of prey items remaining in the gut of larvae during daylight. Thus, the time of day is important when examining RNA/DNA ratios of twaite shad. Generalised additive model of seasonal data showed that water temperature, freshwater pulses and/or turbidity largely contribute to create adequate environments. These might enhance the nutritional condition of twaite shad larvae during the period that they remain in the upper reaches of River Mira.     

Effects of feeding frequency, moist and dry feeds on the growth of Chrysichthys nigrodigitatus Lacépède and on pond water quality

To examine the effects of different feeding frequencies, moist and dry feeds on the growth of Chrysichthys nigrodigitatus Lacépède and on water quality of freshwater ponds, two experiments were conducted. In one experiment, fish stocked at the same densities were subjected to three different feeding regimes using equal quantities of feed. Water quality was monitored and fish growth in the different treatments was compared. To determine the effects of moist and dry feeds, fish growth and water quality in one set of ponds fed with 5% body weight of dry feed were compared to those in another set of ponds stocked at the same rate but fed with 5% body weight of moist feed. Feeding once a day produced the greatest weight gain but fish fed once on alternate days had the best feed conversion, which was associated with pond water that had the highest dissolved oxygen. This suggests that feeding once on alternate days could be adopted as a strategy for feeding fish under unfavourable conditions. Water quality of ponds holding fish fed dry feed was better than that of ponds holding fish fed moist feed, as indicated by oxygen, carbon dioxide and ammonia contents. A highly significant difference in growth (P < 0.01) was found between fish fed moist and dry with feeds: fish performed better when fed with dry feeds.     

Sex organ extracts and artificial hormonal compounds as sex pheromones to attract broodfish and to induce spawning of Chinese black sleeper (Bostrichthys sinensis Lacépède)

Ovarian, testicular and seminal vesicle extracts of mature Chinese black sleeper (Bostrichthys sinensis Lacepede), synthetic steroids 17α‐progesterone (17α‐P), 17α,20β‐dihydroxy‐4‐pregnen‐3one (17α,20β‐P) and prostaglandins PGE₂ and PGF_2α were used in an attempt to attract broodfish and to induce spawning. Furthermore, 17α‐P, PGE₂ and PGF_2α levels were determined in extracts, and PGE₂ and PGF_2α levels were determined in holding and spawning waters. The results showed that ovarian extracts attracted more males than females to enter artificial nests, while testicular and seminal vesicle extracts attracted more females than males. The highest percentage of spawned nests were found when 17α,20β‐P and PGE₂ were administered to the nests, while the largest egg numbers and the mean highest fertilization rate were observed when PGE₂ was added. In ovarian extract, 17α‐P level was higher than levels in testicular or seminal vesicle extracts. The PGE₂ levels were significantly (P<0.05) higher than PGF_2α in the ovarian, testicular and seminal vesicle extracts. The PGE₂ and PGF_2α levels in spawning waters were higher than those in holding waters. The PGE₂ levels were greatly significantly (P<0.01) higher than PGF_2α in spawning and in holding waters. The results suggest that the sex organs of B. sinensis contain 17α‐P, 17α, 20β‐P, PGE₂ and PGF_2α and that 17α‐P, 17α,20β‐P and PGE₂ may act as sex pheromones in this species, attracting both male and female conspesifics to spawning sites and inducing spawning. Among the compounds tested, PGE₂ was the most effective sex pheromone for induction of spawning in B. sinensis.     

Pathology of attachment and vascular damage associated with larval stages of Dissonus manteri Kabata, 1966 (Copepoda: Dissonidae) on the gills of coral trout, Plectropomus leopardus (Lacépède) (Serranidae)

Abstract. Tissue responses in Plectropomus leopardus gills infested with Dissonus manteri copepodid and ehalimus larvae were almost entirely proliferative, with little or no cellular infiltration. The pathological changes were related to attachment, feeding and parasite size, and comprised progressive mechanical erosion, epithelial hyperplasia and fibrosis. When present, infiltrating cells were associated with initial attachment by the copepodid and with the frontal filament basal plate. Approximately 2.4% of the respiratory area was lost as a result of direct vascular damage. Disruption of branchial blood flow resulted from the burrowing and feeding activities of the larvae and compression of adjacent vessels as the parasite increased in size. Chalimus stages were attached by a frontal filament which consisted of a stem with a terminal anchor, and a basal plate in contact with the cartilaginous filament ray. Following chalimus release, the branchial tissue appeared to repair rapidly. No frontal filament remains were found.     

Diet of the largemouth bass, Micropterus salmoides (Lacepède), in Lake Naivasha, Kenya

Abstract The major food items of adult largemouth bass, Micropterus salmoides (Lacepède), in Lake Naivasha, Kenya are not markedly different from those in its native range. Although insects and their larvae are major components of the diet for both temperate and equatorial populations of juvenile bass, the equatorial population also eats Procambarus clarkii (Girard), juvenile fish and aquatic weeds. In temperate populations they also eat crustaceans, rotifers and oligochaetes. The frequency of occurrence of the major prey organisms in the stomachs of M. salmoides varies seasonally with population peaks in these organisms. Similar to North American populations, the Naivasha population feeds during the day between dawn and dusk. In contrast to temperate populations, the population of M. salmoides in this equatorial lake feeds throughout the year, with feeding intensity correlated with water temperature.     

Reproduction of the North American blackbass, Micropterus salmoides (Lacepède), in an equatorial lake, Lake Naivasha, Kenya

Abstract. In contrast to its North American relatives, the Lake Naivasha blackbass, Micropterus saimoides (Lacepdde) has a prolonged spawning season of 8 months between June and January, peaking in August to November. This season is characterized by the presence of high numbers of mature fish with the highest gonadosomatic index (GSI). Analysis of GSI variations in different length-classes reveals that maximum reproduction occurs in the 30-34.9-cm length-class in males and 40-44.9-cm in females. Analysis of the GSI values in the different sampling stations identifies two stations as the breeding areas of M. salmoides in the lake.
The positive correlation between the GSI and the stomach fullness index suggests that the species probably feeds all year round, including the spawning season. Fifty per cent of males and females are mature at 25-29.9-cm and 30-34.9-cm length-classes respectively. The fecundity of fish of 28.4 cm (371 g) to 33 cm (550g) ranged from 1300 to 3524 with a mean of 2203 eggs. Fecundity had no relationship with body length but increased linearly with body weight.     

The pathology of Myxidium giardi Cépède, 1906 infections in wild and cultured eels, Anguilla anguilla L.

Abstract. The histopathology of Myxidium giardi infections in wild and cultured elvers, fingerlings and adult eels is described. The lesions in the target organs of the kidney and gills were minimal. Marked granulomatous changes were evident in the spleen, peritoneal fat and, to a lesser extent, the liver and gas gland. The granulomatous reaction consisted of a mononuclear infiltration into the spore mass and proliferative fibrosis of the surrounding connective tissue, Histological evidence of an immunological response is described. The types of M. giardi cysts are described-a primary interstitial cyst of the kidney and gill, a secondary cyst of the gills and a glomerular spore mass. Primary interstitial cysts in the kidney were observed to rupture and formed spore masses in the interstitial tissue. Evidence of vascular spread and the presence of spore emboli is presented. It is suggested that primary multiplication occurs in the primary interstitial cyst of the kidney and gills, and secondary multiplication in the secondary gill cyst and glomerular spore mass from which mature spores are released to the environment.     

The occurrence and distribution of Myxidium giardi Cépède, 1906 in wild and cultured European eels, Anguilla anguilla L., in England

Abstract. Myxidium giardi was found in wild and cultured eels. The prevalence rate in elvers was 77% in the River Torridge (Devon), 80% in the River Parrett (Somerset) and 90% in the River Ouse (Yorkshire). Adult eels from the River Ouse had a prevalence rate of 53%, Cultured fingerlings and adults had a prevalence rate of 60% and 1% , respectively. There was an apparent age-related pattern in the organ location of the histozoic trophozoite: an initially high prevalence of kidney trophozoites which gradually decreased with age; in the gills of elvers there was a low prevalence of histozoic trophozoites which increased in the adult stage. Histozoic trophozoites were also found in the stomach and intestine of elvers and fingerlings. A qualitative estimate of trophozoite numbers in each organ of elvers is given. The coelozoic trophozoite of M. giardi in the gall bladder of elvers and fingerlings is also described for the first time.     

Effect of substrate on progression and healing of skin erosions and epidermal papillomas of Atlantic halibut, Hippoglossus hippoglossus (L.)

Juvenile Atlantic halibut cultured on a smooth substrate often develop skin lesions on the blind (abocular) side, significantly reducing carcass value and causing economic losses. We discovered that fish not only developed skin erosions, but also extensive epidermal papillomas when held on a smooth substrate for 39 months. This is the first time that epidermal papillomas have been reported in Atlantic halibut. To determine whether substrate type affected the progression or healing of these lesions, fish with papillomas and skin erosions were moved to identical rearing units having either an irregular (sand, gravel or Netlon) substrate, or a smooth (gel-coated fibreglass) substrate. After 62 days, 42-50% of fish held on any of the three irregular substrates had a skin erosion area (SEA) that had either diminished or appeared to be completely healed via gross examination. In contrast, none of the fish held on the smooth substrate showed improvement and 75-100% had a more severe SEA. Changes in the papilloma area (PA) were less dramatic: none of the fish held on an irregular substrate had any clear change in PA, although there was a suggestion that the PA in some fish might becoming less severe. Similarly, none of the fish held on the smooth substrate had a change in PA, although there was a suggestion that the PA in some fish was becoming more severe. After 97 days, there was also a suggestion that specific growth rates were higher in fish held on an irregular substrate when compared with those held on the smooth substrate. Overall, these data further substantiate previous studies suggesting that an irregular substrate, including the commercially used Netlon, is best for rearing Atlantic halibut. While there was a clear relationship between substrate type and whether skin erosions or papillomas progressed or healed, the exact cause(s) of these two responses is uncertain. Future studies should focus on risk factors such as stress, burrowing behaviour and the microenvironment of the substrate.     

Survival of smaller sport caught chinook, Oncorhynchus tshawytscha (Walbaum), and coho, Oncorhynchus kisutch (Walbaum), salmon from Lake Michigan and its management implications

Abstract The survival of small-sized (<50.8 cm) chinook salmon, Oncorhynchus tshawytscha (Walbaum), and coho salmon, Oncorhynchus kitsutch (Walbaum), caught by sport fishing was determined to assess the potential for increasing the size limit for these fish. Fishermen were recently catching smaller salmon than in the 1970s, but salmon growth rates had not changed. To be an effective management option, the survival rate of hooked and returned fish must be high. The overall survival rates were high: 76% for chinook salmon and 70% for coho salmon. There was no significant difference in survival of the coho salmon with size of hook used ( P = 0.31). Any mortality among fish was generally acute; fish hooked deep in the mouth or gills generally bled and died shortly after capture. Fish hooked in the gills had a significantly greater mortality ( P = 0.0002). The overall high survival rate for these species was the result of a small proportion of fish being hooked in the gills or deep in the mouth. Since the survival rate of the salmon was high, the size limit could be increased to allow smaller fish to grow to sizes preferred by sport fishermen.