Survival and sublethal responses of early life stages of pike exposed to low pH in artificial post-mining lake water

The threshold pH for survival of early life stages of pike Esox lucius in post-mining lakes was determined in a laboratory experiment using artificial water characterized by high concentrations of dissolved Ca, Al, Fe, Mn and SO2/4⁻. At pH 3·50–4·00, high mortality was observed before hatching. At pH 4·00 and 4·25, hatching rates were reduced compared with the controls (pH 7·40), and many embryos died in a partly hatched state. Hatching success of embryos exposed to pH levels of 4·50 or higher was not affected. However, at pH 5·00 many newly hatched embryos were deformed. Furthermore, pike exposed to pH 4·00–5·00 did not start feeding. At pH 4·75 and below, mortality increased to 100%, and at pH 5·00, only few eleutheroembryos which were in extremely poor condition survived to the end of the experiment. At pH 5·50, survival was in the same range as in the control group, but growth was reduced. Therefore, early life stages of pike are expected to survive in Lustian post-mining lakes when a pH of 5·50 and above is reached and maintained.     

Habituation to acid in Escherichia coli: conditions for habituation and its effects on plasmid transfer

Induction of acid resistance (habituation) in Escherichia coli at pH 5·0 took ca 5 min in broth at 37°C and 30–60 min in minimal medium. Induction occurred at a range of pH values from 4·0 to 6·0; it was dependent on continuing protein and RNA synthesis but substantial acid resistance appeared in the presence of nalidixic acid. Acid resistance was long-lasting; organisms grown at pH 5·0 retained most of their resistance after 2 h growth at pH 7·0. Organisms grown at pH 5·0 showed increased synthesis of a number of cytoplasmic proteins compared with the level in cells grown at pH 7·0. DNA repair-deficient strains carrying recA, uvrA or polAl mutations were more acid-sensitive than the repair-proficient parents but were able to habituate at pH 5·0. Organisms grown at pH 5·0 transferred the ColV plasmid much more effectively at acid pH than did those grown at pH 7·0 and habituated recipients appeared better able to repair incoming acid-damaged plasmid DNA than did those that were non-habituated. Induction of acid resistance at pH 5·0 may be significant for the survival of organisms exposed to periodic discharges of acid effluent in the aquatic environment and habituation may also allow plasmid transfer and repair of acid-damaged plasmid DNA during or after such exposure.     

Fate of low temperature and acid-adapted Yersinia enterocolitica and Listeria monocytogenes that contaminate lactic acid decontaminated meat during chill storage

Pathogens found in the environment of abattoirs may become adapted to lactic acid used to decontaminate meat. Such organisms are more acid tolerant than non-adapted parents and can contaminate meat after lactic acid decontamination (LAD). The fate of acid-adapted Yersinia enterocolitica and Listeria monocytogenes, inoculated on skin surface of pork bellies 2 h after LAD, was examined during chilled storage. LAD included dipping in 1%, 2% or 5% lactic acid solutions at 55°C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at ≈1–1·5 pH units below that of water-treated controls. Growth permitting pH at 4·8–5·2 was reached after 1% LAD in less than 0·5 d (pH 4·8–5·0), 2% LAD within 1·5 d (pH 4·9–5·1) and after 5% LAD (pH 5·0–5·2) within 4 d. During the lag on 2% LAD meat Y. enterocolitica counts decreased by 0·9 log₁₀ cfu per cm² and on 5% LAD the reduction was more than 1·4 log₁₀ cfu per cm². The reductions in L. monocytogenes were about a third of those in Y. enterocolitica . On 1% LAD the counts of both pathogens did not decrease significantly. The generation times of Y. enterocolitica and L. monocytogenes on 2–5% LAD meats were by up to twofold longer than on water-treated controls and on 1% LAD-treated meat they were similar to those on water-treated controls. Low temperature and acid-adapted L. monocytogenes and Y. enterocolitica that contaminate skin surface after hot 2–5% LAD did not cause an increased health hazard, although the number of Gram-negative spoilage organisms were drastically reduced by hot 2–5% LAD and intrinsic (lactic acid content, pH) conditions were created that may benefit the survival and the growth of acid-adapted organisms.     

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon ( Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.     

Effect of dietary cortisol administration on growth and reproductive success of channel catfish

The effect of cortisol administration on reproductive performance was investigated in channel catfish Ictalurus punctatus broodfish. Cortisol was added to a commercial catfish feed by dissolving in ethanol and spraying the feed to yield a dietary concentration of 150 mg kg⁻¹ feed. The cortisol diet and the control (no cortisol) diet were offered at a rate of 1% of biomass to three replicate ponds each containing 28 female and 14 male broodfish, respectively, three times per week for 11 weeks. Spawning began 10 days after the start of the experiment, and continued for 10 weeks. In fish fed cortisol, body mass and the hepato‐somatic index were reduced ( P  ≤ 0·02) and concentrations of plasma cortisol and glucose were significantly higher ( P  ≤ 0·0003) compared to those of controls. The relative frequency of spawning was similar between the two treatments; however, cortisol‐fed channel catfish had an average of 47·1% more spawns than the control‐fed fish. On average, there were 25·5 spawns per pond in the treated groups compared to 12·3 spawns per control pond ( P  = 0·10). No effect was observed on egg production, with individual egg mass, fecundity, and hatching success being similar ( P  ≥ 0·27) for both treatments. Despite the observed negative effects of cortisol on somatic and hepatic growth, the increased reproductive output coupled with no observable effects on the eggs or hatching success demonstrates that cortisol does not suppress channel catfish reproduction.     

Induction of gynogenesis and gonad development in the muskellunge

Muskellunge Esox masquinongy eggs activated with UV-irradiated yellow perch Perca flavescens sperm were subjected to heat shock at 31 ± 1° C for 6 min, 20 min after fertilization in three experiments. Survival at eyed stage was 1·7 ±1·6, 6·8 ± 4·8 and 2·3 ±0·5% in experiments I, II and III, respectively. After rearing the gynogenetic muskellunge in troughs and then in ponds, the sex ratio of gynogens in experiment I did not significantly (P>0·05) differ from the expected ratio 0:1 (male: female), however, one male and one intersex were observed. In experiments II and III, the sex ratio of gynogens differed significantly from expected (0 : 1). Three months after hatching, the growth of females did not significantly (P>0·05) differ among control and gynogenetic groups, whereas male growth was significantly (P<0·01) higher in the control v. gynogenetic group. The histological structures of the gynogenetic fish gonads in both sexes were similar to those described in the gonads of control muskellunge. After the overwintering period, signs of active spermatogenesis were observed in the testis of 1 + year old gynogenetic fish, whereas ovaries contained only oocytes at the perinucleolar stage. At this stage, plasma sex steroids testosterone (T) and oestradiol-17β (E2) cannot be used to discriminate the sex of gynogenetic muskellunge, as intersex, male and female fish had similar levels of T and E2.     

Effects of environmental factors on survival, growth, and production of American shad larvae

Episodic increases in temperature of 5°C above 20° C, over 48 h or declines in pH of 1·0 unit from pH 7·0 reduced survival of yolk-sac and feeding-stage larvae of American shad Alosa sapidissima . Over 16 days all measures of survival, growth, and production were more favourable at each higher temperature in the 15–25° C range. More favourable responses were also obtained at the higher prey level (500 v . 50 Artemia nauplii l^-1) and at the higher pH (7·5 v . 6·5). Combinations of high temperature and high prey levels, at pH 7·5, led to highest larval production. Little growth or production occurred at 15° C, regardless of pH or prey level. The effect of pH was strong with respect to survival, but weak with respect to growth. In attempts to restore American shad populations by larval stocking, release times and sites can be critical to optimize survival and eventual returns. Releases of larvae potentially will be most effective when made at temperatures >20° C, pH>7·0, and prey levels >50 1^-1. These conditions are most likely to occur in Maryland tributaries of Chesapeake Bay between mid-May and early June.     

The Development of Aerobic Spoilage Flora on Meat Stored at Chill Temperatures

In meat juice medium, aerobic spoilage bacteria utilized the following substrates in the order shown: Pseudomonos , glucose, amino acids, lactic acid; Acinetobacter , amino acids, lactic acid: Enterobacter , glucose, glucose-6-phosphate, amino acids; Microbacterium thermosphactum , glucose, glutamate. All the bacteria grew at their maximum rate utilizing the first and second substrates, but the growth rates declined when these were exhausted. The growth rate of Acinetobacter was reduced at pH 5·7 and below. All other species grew at their maximum rate within the pH range 5·5–7·0. On meat pseudomonads grew faster than the other species at all temperatures between 2° and 15°C. Interactions between any two species were observed only when one organism had attained its maximum cell density. Substrate exhaustion at the meat surface did not limit bacterial growth and it is suggested that the maximum cell density of aerobic spoilage cultures is determined by oxygen limitation of growth.     

Isolation and growth physiology of novel thermoactinomycetes

A total of 34 thermophilic isolates identified as members of the genus Thermoactinomyces by a range of chemotaxonomic, microscopic and determinativebiochemical tests, were isolated from two acid soils. Growth studies in shake flask and fermenteridentified the isolates to be moderately acidophilic with growth occurring between pH4·5 and 6·0 with optima at pH 5·0. The isolates differed considerablyfrom known Thermoactinomyces cultures in their pH profile, colony morphology andin several biochemical tests.Extracellular enzyme activities are identified and partiallycharacterized in termsof their thermostability, pH and temperature profiles from crude supernatantfluid samples. Optimal protease, amylase and pullulanase activity was observed at pH5·0–5·5 and 75–80 °C with each showing T ₍₅₀₎ values of 10, 30 and 30 min, respectively. A highly thermotolerant extracellularesterase was also identified which retained 50% activity after 8 h at 90°C . This is the firstreport of an acidophilic member of the genus Thermoactinomyces.     

Water pH and urinary excretion in silver catfish Rhamdia quelen

The effect of acute exposure to different water pH levels on urinary excretion and plasma ion levels in silver catfish Rhamdia quelen was analysed. Fish were exposed to pH 4·0, 5·0, 7·5, 8·0, and 9·0 for 4 days and urine was collected. Other specimens were also exposed to the experimental pH for 24 h and blood was sampled. Urine flow rate, urine and plasma pH showed a significant trend to increase with the increase of water pH. Urinary Na⁺ excretion rate also increased and ammonia urinary excretion rate decreased with the increase of water pH. There was a significant trend to decrease volume, ammonia, Cl⁻ and Na⁺ urinary excretion rate with increasing mass in fish exposed to all pH levels studied. Plasma ammonia levels showed a slight decrease in fish exposed to water pH from 4·0 to 8·0, but those exposed to water pH 9·0 presented the highest ammonia levels. Most plasma ions and urinary excretion changes observed in silver catfish exposed to acidic or alkaline water were similar to those already detected in rainbow trout Oncorhynchus mykiss . In addition, the kidney and urinary bladder might participate on acid–base balance in silver catfish, since urine pH changed according to plasma pH.     

A field investigation of water quality, fish and invertebrates in the Mawddach river system, Wales

A 3-year study was made of the soft, acid waters of the Rivers Mawddach, Wen and Gain, which contained copper, zinc and iron from natural outcrops and abandoned mines. Invertebrates, typical of acid to neutral streams, were present but there was no pattern in overall numbers or in biomass between stations. However, the abundance and distribution of Ephemeroptera were related to pH and water hardness although not to copper and zinc. Brown trout, Salmo trutta , were present and there was little difference in rate of growth between stations, whereas biomass and population density varied considerably between stations, being related to water quality such that, where annual median and 95-percentile of the summed proportions ( p ) of the threshold LC50 concentrations of copper and zinc to rainbow trout, S. gairdneri were 0·3 and 0·7 respectively, biomass was half that in the absence of the metals and, where they were 0·6 and 1·3 respectively, no fish would be expected to occur. Low pH was an additional adverse factor at some locations. Salmon, S. salar , failed to populate a tributary where the sum of the p t LC50 values of copper and zinc was 0·45. High aqueous concentrations of copper resulted in elevated concentrations of copper in the liver of trout, especially in older fish, but not in the muscle. Concentrations of zinc in fish liver and muscle were low despite high ambient concentrations.     

Differential effects of low pH and aluminium on the caudal neurosecretory system of the brook trout, Salvelinus fontinalis

Brook trout were subjected to soft water at pH 6·5, 5·5 or 5·0 without aluminium added, or to water at pH 5·5 with 200,300 or 500 μg Al I^-1 added. The response of the caudal neurosecretory system to low pH or aluminium was evaluated after one week by measuring the urotensin I and urotensin II concentrations in the urophysis by radioimmunoassay, and by morphometric analysis of the caudal neurosecretory cells. A positive correlation was found between urotensin I concentrations and acidity, and a negative correlation was found between urotensin II concentrations and total aluminium in the water. Morphometric indices (cell size and proportion of lobed nuclei in the caudal neurosecretory cells) suggested increased synthetic activity in the caudal neurosecretory cells of fish at pH 5·5 compared to pH 6·5.     

The effect of acid water on the hatching of salmonid eggs

The survival of salmon Salmo salar , sea trout and brown trout Salmo trutta eggs in acid water in the range pH 3·5±7·0 was investigated over a period of three winters. The effects of fertilising the eggs in acid water at pH 4·0, 4·5 and 5·0, and dilution of the test media were also studied. There was considerable yearly variation in the numbers of eggs which hatched, but there were no marked differences between the three species in the tolerances of the eggs to acid water; pH 3·5 was lethal within 10 days to all the eggs, but at pH 4·5 and higher pH levels there was no obvious difference in hatching attributable to acidity.     

Influence of spawning on swimming performance and muscle contractile properties in the short-horn sculpin

The total distance travelled during the first two kinematic stages of the escape response of short-horn sculpin was significantly greater in post spawning fish (0·41 L) than in gravid fish (0·23 L). The maximum velocity of the snout during the C-bend was significantly higher (5·6 L s⁻¹) in postspawning fish than in gravid fish (3·8 L s⁻¹). To investigate some of the mechanisms underlying changes in swimming performance, the contractile properties of fast muscle fibres were determined in fish of similar body length. The rate of tetanic force relaxation (time from last stimulus to 50% peak force) was 34% faster in gr avid than in postspawning fish. Maximum contraction velocity, determined by the slack-test method, was significantly higher in gravid than in postspawning fish (6·8 v . 5·9 muscle lengths s⁻¹). In contrast, both maximum isometric stress and power output (determined from the force–velocity relationship) were >50% higher in fibres from postspawning than from gravid fish, even though myofibrillar protein and water contents were similar (120 mg g⁻¹ wet mass and 86% of body mass, respectively). The results show that swimming performance and the contractile properties of fast muscle fibres vary with the reproductive cycle in short-horn sculpin acclimated to the same photoperiodic and temperature regime.     

The effect of citric acid on growth of proteolytic strains of Clostridium botulinum

In strictly anaerobic conditions in a culture medium adjusted to pH 5·2 with HCl and incubated at 30°C, inocula containing < 10 vegetative bacteria of Clostridium botulinum ZK3 (type A) multiplied to give > 10⁸ bacteria per ml in 3 d. Growth from an inoculum of between 10 and 100 spores occurred after a delay of 10–20 weeks. Citric acid concentrations of 10–50 mmol/l at pH 5·2 inhibited growth from both vegetative bacteria and spore inocula, a concentration of 50 mmol/l increasing the number of vegetative bacteria or of spores required to produce growth by a factor of approximately 10⁶. The citric acid also reduced the concentration of free Ca²⁺ in the medium. The inhibitory effect of citric acid on vegetative bacteria at pH 5·2 could be prevented by the addition of Ca²⁺ or Mg²⁺ and greatly reduced by Fe²⁺ and Mn²⁺. The addition of Ca²⁺, but not of the remaining divalent metal ions, restored the concentration of free Ca²⁺ in the medium to that in the citrate-free medium. The inhibitory effect of citric acid on growth from a spore inoculum was only partially prevented by Ca²⁺. Citric acid (50 mmol/l) did not inhibit growth of strain ZK3 at pH 6 despite the greater chelating activity of citrate at pH 6 than at pH 5·2. The effect of citric acid and Ca²⁺ at pH 5·2 on vegetative bacteria of strains VL1 (type A) and 2346 and B6 (proteolytic type B) was similar to that on strain ZK3.     

Effects of surgically implanted transmitters on swimming performance, food consumption and growth of wild Atlantic salmon parr

Experiments were conducted on wild Atlantic salmon Salmo salar parr to determine the effect of surgically implanted dummy transmitters on swimming performance, food consumption and growth. Swimming performance of tagged fish (tag 1·7–3·7% of fish mass) was similar to that of control fish 1, 5 and 10 days after surgery. Negative effects on growth, however, were found up to day 36 of a 45 day experiment (tag 0·9–2·6% of fish mass). Consumption rates were similar between tagged and control fish and did not explain differences in growth.     

Maternal transfer of cadmium tolerance in larval Oreochromis mossambicus

Exposing female tilapia to Cd did not affect reproduction and egg quality, nor the survival of their offspring. The LT ₅₀ of Cd-exposed larvae (within 24 h post hatching) from Cd-treated female Oreochromis mossambicus (mean ±S.E.=10·9±0·5 days, n =4) was greater than that of Cd-exposed larvae from control females (6·9± 1·2 days, n =4). A substantial amount of metallothionein mRNA (MT mRNA) was found in both oocytes and newly hatched larvae from Cd-treated females, but MT mRNA levels were low in newly fertilized eggs. The amount of MT mRNA was very low in all these stages in the control group. Cadmium could not be detected at any stage for either control or Cd-treated group, and metallothionein protein levels were also very low in both groups. The early appearance of MT mRNA in oocytes and newly hatched larvae from Cd-treated females may result in early translation after hatching and explain their tolerance to Cd.     

Effects of graded hypoxia on Atlantic salmon infected with amoebic gill disease

Atlantic salmon Salmo salar with amoebic gill disease (AGD) were exposed to a graded hypoxia (135–40 mmHg water P O₂) and blood samples analysed for respiratory gases and pH at 119, 79·5 and 40 mmHg water P O₂. There were no differences in the rate of oxygen uptake between infected and control fish. However, arterial P O₂, and pH were significantly lower in the infected fish whereas P CO₂ was significantly higher in infected fish compared with controls prior to hypoxia and at 119 mmHg water P O₂. At 79·5 and 40 mmHg water P O₂ saturation, there were no significant differences in blood P O₂ or pH although blood P CO₂ was elevated in AGD affected fish at 50% hypoxia (79·5 mmHg water P O₂). The elevated levels of P CO₂ in fish affected by AGD resulted in a persistent respiratory acidosis even during hypoxic challenge. These data suggest that even though the fish were severely affected by AGD, the presence of AGD while impairing gas transfer under normoxic conditions, did not contribute to respiratory failure during hypoxia.     

Reproductive sensitivity to elevated water temperatures in female Atlantic salmon is heightened at certain stages of vitellogenesis

In order to compare the effects on reproductive performance of short-term or prolonged exposure to elevated temperatures during vitellogenesis, female Atlantic salmon Salmo salar were held at a water temperature of 22° C for periods of 4 or 6 weeks during the austral summer and autumn. Plasma levels of 17β-oestradiol (E₂), testosterone (T) and vitellogenin (Vtg) were monitored and reproductive success was compared to that in groups of fish maintained at 14 or 22° C for 12 weeks from mid-January. Significant endocrine effects were observed within as few as 3 days of the commencement of exposure to 22° C, when plasma levels of E₂ ( c. 0·5 ng ml⁻¹) and Vtg ( c. 1·4 mg ml⁻¹) were approximately half those observed in fish maintained at 14° C ( c. 1·0 ng ml⁻¹ and 2·7 mg ml⁻¹ respectively). The fertility and survival to the eyed stage of ova from fish held at 14° C exceeded 85 and 70% respectively, whereas ova from fish held at 22° C for 6 or 12 weeks exhibited significantly reduced fertility (<70 and <45% respectively) and survival ( c. 40 and 13% respectively). In spite of significant endocrine effects at all stages, a 4 week exposure to 22° C only generated significant reductions in egg fertility (<65%) and survival ( c. 30%) when it occurred between mid-February and mid-March. Together, these data confirm that high temperature spikes can affect reproductive success as strongly as more prolonged exposures, and indicate that there is a critical period of reproductive sensitivity to elevated temperature in late February and early March in this stock of Atlantic salmon.