Aquarium Trials Research Articles

Reduced Infestation Levels of Lepeophtheirus salmonis in Atlantic Salmon (Salmo salar) following Immersion Exposure to Probiotic Aliivibrio spp.

Salmon lice (Lepeophtheirus salmonis) constitute a major challenge during the production of farmed Atlantic salmon in Norway. Preventive measures are considered to have a higher impact on sustainable control than lice treatment. Therefore, the studies presented here aimed to document the preventive effects of probiotic Aliivibrio spp. on lice infestation in experimental challenges. A reduction in salmon lice attachment success (58–65%) was observed in two separate aquarium trials, where Atlantic salmon were exposed to different compositions of Aliivibrio species 91 and 155 days prior to lice challenge. In a third trial, no difference in attachment was observed in groups exposed to probiotics 58 days prior to lice challenge compared to controls. However, a relative reduction in lice counts was seen on movable stages later in the trial. High levels of probiotic bacteria had no impact on lice viability in an in vitro bioassay on the preadult life stage; thus, the mechanism behind the preventative effect remains unknown. In conclusion, probiotic Aliivibrio bacteria can likely be used as a preventive tool to reduce salmon louse infestations in the salmon industry. The mechanism is still unknown, and this novel approach to lice control warrants further investigation to understand its optimal use and potential.

Detection of fish species composition using environmental DNA in aquarium trials

Detection of fish species composition using environmental DNA in aquarium trials

Unstable intraguild predation causes establishment failure of a globally invasive species.

Biotic resistance is often posited, but rarely known, to be the cause of invasion failure. Competition and predation are the most frequently identified processes that may prevent or limit the establishment of nonnative species. Interactions between nonnative and native species that involve intraguild predation (IGP) are very common in nature, although theory predicts most IGP systems should be unstable and lead to extinction. If this prediction is true, the frequency of invasion failures due to IGP may be underappreciated because of their fleeting nature and, thus, studies of unstable IGP systems are lacking, despite the opportunities they offer for understanding the factors affecting their unstable dynamics. We investigated a failed invasion involving an IGP relationship. In Florida, the guppy (Poecilia reticulata), a worldwide invader, fails to establish in the presence of eastern mosquitofish (Gambusia holbrooki). We tested whether and how resident mosquitofish cause guppy invasion failure using replicated mesocosm and aquarium trials. Both the predator and competitor components of the IGP relationship were strongly asymmetrical, with large impacts on guppies. We identified two effects, direct consumption of neonates and aggressive interference competition, that limited survival and recruitment. The highly unstable nature of this IGP relationship is the primary cause of the failure of the guppy to establish in Florida. Our study shows that the transient nature of an ephemeral IGP relationship can yield important insights into the underlying causes of invasion failure, including the role of strong biotic resistance.

Size matters: large spiny lobsters reduce the catchability of small conspecifics

Indices of lobster abundance and population demography are often derived from pot catch rate data and rely upon constant catchability. However, there is evidence in clawed lobsters, and some spiny lobsters, that catchability is affected by conspecifics present in pots, and that this effect is sex- and size-dependent. For the first time, this study investigated this effect in Panulirus cygnus, an economically important spiny lobster species endemic to Western Australia. Three studies: (1) aquaria trials, (2) pot seeding experiments, and (3) field surveys, were used to investigate how the presence of large male and female conspecifics influence catchability in smaller, immature P. cygnus. Large P. cygnus generally reduced the catchability of small conspecifics; large males by 26-33% and large females by 14-27%. The effect of large females was complex and varied seasonally, dependent on the sex of the small lobster. Conspecific-related catchability should be a vital consideration when interpreting the results of pot-based surveys, especially if population demography changes. Analysis of the mean catch rate of large P. cygnus over the past 29 yr indicates that fishery management changes have created significant variations in the abundance of large lobsters. This is likely to have affected the catchability of smaller lobsters, which will have implications for the use of time series catch rate data in the stock assessment and management of this fishery.

Local Ecosystem Uptake of Stocked Trout by Cambarus bartonii and the Relevance of Prior Exposure to Stocking

We assessed variation in feeding preference of Cambarus bartonii (Appalachian Brook Crayfish) for stocked Salmo trutta (Brown Trout) or wild Salvelinus fontinalis (Brook Trout) across 8 central Pennsylvania headwater streams with different recent exposures to trout stocking. In separate trials, we allowed crayfish to interact with and choose between fillets of stocked Brown Trout or wild Brook Trout in either a flowing Y-apparatus or a standing-water aquarium. In the Y-apparatus trials and standing water aquarium trials, crayfish exhibited no detectable feeding preference based on proximity to stocking sites from which they were collected. In the Y-apparatus trials, crayfish were more likely to move towards a fillet type than not. Overall, our results provide evidence that crayfish do not distinguish between stocked Brown Trout and wild Brook Trout as food sources, and history of exposure to stocked trout does not influence feeding preference. Specifically, crayfish accept stocked trout as a food source, even if this resource is new to the environment (i.e., with the additions of new stocking sites in previously unstocked streams). Acceptance of stocked trout as a food resource suggests crayfish may play an important role in the local incorporation of this significant allochthonous nutrient input. Future research should address if local uptake of stocked trout by crayfish is able to mitigate downstream nutrient loads related to stocking.

Ion concentrations in seagrass: A comparison of results from field and controlled-environment studies

Osmoregulation is essential for the survival of seagrasses in marine and hypersaline environments. The aim of this study was to examine ion concentrations of four seagrass species (Posidonia australis, P. sinuosa, Amphibolis antarctica and A. griffithii) after exposure to salinity changes. Plant fragments were placed in a series of aquaria at marine salinity (35) and, after one week of acclimation, exposed for 7 days to salinities between 20 and 70. Cl−, Na+ and total ion concentration increased with salinity in leaf tissue of the four seagrasses species. These results were compared with those of P. australis and A. antarctica samples collected at three locations at Shark Bay, Western Australia where higher salinities occurred, ranging from 46 to 51. Concentrations of K+ and Ca+2 were higher in seagrass tissues from Shark Bay than in those in aquarium trials. Cl−, Na+ and total ions in P. australis and A. antarctica from Shark Bay were lowest at the highest salinity location. The K+/Na+ ratio in the aquarium trials (under ambient conditions) was in the following order: A. antarctica = A. griffithii > P. australis > P. sinuosa and Ca+2/Na+ ratio was: A. antarctica = A. griffithii > P. sinuosa > P. australis. This species order indicates a physiological capacity to tolerate variation in salinity. Furthermore, these ratios were higher in the locality with highest salinity in Shark Bay, indicating acclimation and adaptation of ion concentrations to the salinity regime in the environment.

Seasonal nutritional status in Norway lobsters, Nephrops norvegicus (L.): are females nutritionally compromised over the winter?

ABSTRACTNorway lobsters, Nephrops norvegicus, are sediment-dwelling decapod crustaceans that excavate burrows from which they make short excursions to feed by predation and scavenging. The females of this species are known to reside within their burrows for an extended period of time over the winter while brooding their eggs. The aim of this study was to assess the likelihood of these females being able to feed during this brooding period. Biophysical and biochemical measurements that had previously been shown to change with starvation under laboratory conditions in male N. norvegicus were taken for female N. norvegicus under similar conditions. These measurements were also compared in both sexes obtained from monthly trawl samples from the Clyde Sea Area, Scotland, UK, together with trawl composition data. The laboratory study showed that the hepatosomatic index, and the copper, lipid and water content of the hepatopancreas can be used as indicators of the state of starvation in females, as in males. In the wild, both sexes have reduced nutritional status during the winter, but not to the degree seen in animals starved for 20 weeks in aquarium trials. This study does not support the hypothesis that females cease feeding over winter, during their brooding period. Firstly, some females were unable to sustain ovary development during starvation under controlled conditions, contrary to field observations. Secondly, field data suggest that there is no sex-specific reduction in nutritional status.

An accurate tool for ageing Two‐spined Blackfish for use in determining timing of spawning in upland streams in the Brindabella ranges, ACT, Australia

SummaryTo manage populations of threatened fish species in modified habitats and regulated rivers requires an understanding of their reproductive biology and spawning cues. In particular, accurate information about early life stages in these species can be used to facilitate programmes that maximise recruitment and breeding success. This study aimed to develop methods to accurately age early juvenile freshwater native fish, Two‐spined Blackfish, (Gadopsis bispinosus), to allow the determination of spawning date. This was accomplished through the examination of otolith microstructure in early juveniles. The age at which the first ring was deposited and the relationship between days and number of rings were determined using both field and aquarium trials. Field trials of marked juvenile otoliths revealed daily deposition of rings (1.02 ± 0.02 rings per day for fish sacrificed six days postmarking). The strength of this relationship lessened slightly as juveniles aged (0.92 ± 0.02 rings per day for fish sacrificed 13 days postmarking). The first otolith ring was deposited 7.50 ± 1.09 days after spawning. The enumeration of daily rings combined with knowledge of the commencement of ring deposition enabled accurate estimation of spawning date. The current study is the first to examine otolith microstructure in juvenile Two‐spined Blackfish allowing accurate determination of spawning date. While more research is required to accurately age older juveniles, this technique has the potential to precisely correlate spawning with environmental cues, facilitating better management of temperature and flow during breeding periods, potentially increasing spawning and recruitment of this endangered species.

Development of molecular markers for eDNA detection of the invasive African jewelfish (Hemichromis letourneuxi): a new tool for monitoring aquatic invasive species in National Wildlife Refuges

The genetic material (DNA fragments of cellular or extracellular origin) that organisms leave behind in nonliving components of the environment such as water, soil, or sediments is defined as environmental DNA (eDNA). Recently, the use of eDNA has been recognized as an effective method for aquatic invasive species early detection and surveillance. We developed molecular markers for eDNA detection of the African jewelfish (Hemichromis letourneuxi) in and around Loxahatchee National Wildlife Refuge, Florida. The lower limit of detection using these markers was determined as well as the effect of fish density and time on detection using controlled experiments. Specificity and sensitivity of these markers was tested in aquarium trials and also in field samples. Results showed that developed markers (probe and primers) for Taqman assays were sensitive and specific for eDNA detection via traditional and quantitative PCR methods (qPCR). The observed theoretical minimal qPCR detection level, based on standard curve analysis for this species, was approximately 0.0002 ng/uL (R 2 = 0.90) at a PCR cycling threshold (CT) of 28.5–29. There was a positive and significant relationship between fish density and eDNA detection with detection probabilities ranging from 0.32–1.00 depending on fish density. A negative and significant relationship between average CT values and density further corroborated our findings that target eDNA increased with increasing fish density. Developed markers detected the presence of H. letourneuxi in the canal adjacent to but not in Loxahatchee National Wildlife Refuge. The single positive found in the canal adjacent to Loxahatchee National Wildlife Refuge showed a similar CT value to the observed average for density of three fish per aquarium.

When habitat complexity increases predation risk: experiments with invasive and neotropical native fishes

We tested the predator–prey relationships between a native piscivore (Salminus brasiliensis) and introduced and native fish species of the Paraná River, Brazil. We hypothesised that S. brasiliensis can exert biotic resistance against invasive fishes but not at the same degree for all species. Three invasive (Cichla piquiti, Oreochromis niloticus and Ictalurus punctatus) and two native (Astyanax altiparanae and Prochilodus lineatus) species were offered as prey to S. brasiliensis in 300 L aquaria trials at three levels of cover (0%, 50% and 100% of artificial macrophytes). S. brasiliensis had a greater ability to capture prey in complex habitats, so predation success did not decrease with habitat complexity and even increased on I. punctatus. Prey survival was variable through time and among species, being high for I. punctatus. The three most consumed species (P. lineatus, C. piquiti, and O. niloticus) were less active and occupied the aquaria surfaces, changing strongly their behaviour with habitat complexity. Except for P. lineatus and C. piquiti, S. brasiliensis preferably preyed on smaller individuals of the other species. Our experiments support that S. brasiliensis is an interesting candidate to resist the invasion by C. piquiti and O. niloticus but not to control the abundance of I. punctatus.

Estimates of exploitation rates of the spiny lobster fishery for Panulirus argus from tagging within the Bahía Espíritu Santo ‘Sian Ka'an’ Biosphere Reserve, Mexican Caribbean

The Caribbean spiny lobster (Panulirus argus) fishery is currently being assessed for a certification process. It is the main economic activity within the Biosphere Reserve of Sian Ka'an-Mexico (SK), which is a marine-protected area where restricted access fishing is allowed. In this study, commercial catch rates were examined, and lobsters over a wide size range were tagged throughout the 2010/2011 fishing season, to assess fishing mortality rates and movement patterns in Bahía Espíritu Santo-SK. Lobster tag recovery data were aggregated into 2-week periods and analysed using a modified Brownie model that was parameterized to account for lobster tag-reporting, and the lobster tag-retention rates. This allowed the estimation of instantaneous rates of natural and fishing mortality, considering catchability and fishing effort. Independent aquaria trials were conducted to better estimate lobster tag retention, tagging-induced mortality and interviews with fishermen were conducted to better estimate lobster tag reporting. Based mainly on legal-sized juveniles with fast growth rates found in casitas, the stock is subject to fishing to a maximum depth of 20 m, because of the prohibition of SCUBA diving and the use of other fishing gear. The Brownie model indicated that exploitation rates within this bay area were high,>0.94. Changes in catch per unit of effort and catchability throughout the season explain how the ‘casita/campo’ system allows for a seasonal replenishment of juveniles and adults, which has kept the landings relatively stable for the past decade.

Revisiting the functional roles of the surgeonfish Acanthurus nigrofuscus and Ctenochaetus striatus

Investigating the functional role of herbivorous fish species is important for understanding reef resilience and developing targeted management plans. Among the most abundant fish species on Indo-Pacific coral reefs are the surgeonfishes Acanthurus nigrofuscus and Ctenochaetus striatus. A. nigrofuscus is an herbivorous grazer that crops filamentous algae from the epilithic algal matrix, while C. striatus is detritivorous and was thought to ‘brush’ detritus from the surface of filamentous algae, causing little damage to algal strands. Although the foraging mechanisms and general diet of these surgeonfishes have been established, their grazing impact on epilithic algal turfs has been unclear. This is the first study to quantify the grazing impact of A. nigrofuscus and C. striatus on algal turfs. Through aquaria trials using epilithic algal turf grown on experimental tiles, we found that both A. nigrofuscus and C. striatus consistently fed more intensively upon sparse/short algal turfs even though the yield of algae per bite was greater for dense/long algal turfs. As there was no difference in the nutritional value of sparse and dense algal turfs, we hypothesise that A. nigrofuscus avoided dense turf due to its significantly greater sediment load than sparse turf, while C. striatus likely avoided dense turf as it would become entangled in their bristle-like teeth. Unexpectedly, despite its dental morphology, C. striatus removed significantly more algal turf per hour than A. nigrofuscus, irrespective of canopy height. The capability of C. striatus to remove significant quantities of algal turf through their foraging activity implies that this abundant and widespread species may substantially affect algal turf dynamics. If this is the case, the exclusion of detritivorous Ctenochaetus species from herbivorous fish functional groups used in resilience monitoring will need to be re-evaluated.

Advances in tagging syngnathids, with the effects of dummy tags on behaviour of Hippocampus guttulatus

Artificial marking and tagging techniques have been used to study movement, population dynamics, behaviour, ecology, survival and growth of at least 25 syngnathid species. External necklace-style tags and injection of visible implant elastomer have been the most used techniques, uniquely identifying hundreds of individual syngnathids to study population dynamics, mortality, behaviour, ecology and growth in at least 13 and 12 species, respectively. Only two studies, both on larger syngnathid species, have tested the use of internal or electronic tags. This new case study reveals that dummy tags, weighing up to 6% of individual body mass, have minimal effect on normal ex situ behaviour of the long-snouted seahorse Hippocampus guttulatus, a smaller syngnathid. In paired aquarium trials, tags did not affect movement, holdfast use or general behavioural state, and only had a short-term effect (1 day) on vertical orientation. Tagged H. guttulatus gained more mass during the 5 day trials, a result which warrants further exploration but indicates that tags did not reduce feeding. This study shows promise for using electronic tagging to study H. guttulatus and similarly sized syngnathids in the wild.

Guppy populations differ in cannibalistic degree and adaptation to structural environments

There is considerable variation in cannibalism between different species and also between individuals of different species, although relatively little is known about what creates this variation. We investigated the degree of cannibalism in guppy (Poecilia reticulata) populations originating from high and low predation environments in Trinidad, and also how cannibalism was affected by the presence of refuges. Females from two populations were allowed to feed on juveniles from two populations in aquaria trials. The cannibalism was size-dependent and varied depending on both juvenile and female origin. Low predation females were more efficient cannibals and low predation juveniles were better at avoiding cannibalism compared to high predation guppies when no refuges were present. The high predation females were superior cannibals and the high predation juveniles were better at escaping cannibalism than the low predation guppies when refuges were present. We discuss whether the differences in cannibalism and response to refuge addition relate to predation-induced habitat shifts and differences in the guppies' natural environment.

Biology and preliminary host range of Hydrotimetes natans Kolbe (Coleoptera: Curculionidae), a natural enemy candidate for biological control of Cabomba caroliniana Gray (Cabombaceae) in Australia

Abstract Cabomba caroliniana, otherwise known as cabomba, is a submerged, rooted macrophyte with heavily dissected leaves that produces flowers that extend above the water surface. It has been disseminated around the world by aquarium traders and enthusiasts, and has become a noxious weed in numerous countries, including Australia, where it often produces dense monospecific stands. It is considered native to southern parts of North and South America, and is a common plant in floodplain streams and lakes in north‐east Argentina. Because of the lack of alternative control methods, a search for biological control agents was initiated in 2003. The most promising natural enemy found during surveys of C. caroliniana in Argentina was the aquatic weevil Hydrotimetes natans. The entire life cycle is completed on the plant, primarily underwater, except when the adults climb onto emergent flowers to mate. Larvae mine the stems, pupal cases are constructed in the leaf axils where the petiole joins the stem, and adults feed on the leaves and the stems, primarily at the growing tips. Field surveys of C. caroliniana and other submerged plant species, as well as results from preliminary laboratory host range trials suggest that the weevil is specific to cabomba. Adults were found only on other plant species when intertwined with C. caroliniana in the field and did not move onto other plant species in aquaria trials. The distribution of the larvae in the field was studied in relation to depth and plant size. No preferences for stem width or plant length were found, although a significant portion of the larval mines were located near the root crown of the plant. This information on the host specificity and biology of H. natans in its native range may guide researchers studying the laboratory fundamental host range and determining the potential effectiveness of the weevil for biological control of cabomba in its introduced range.

Ulcerative disease outbreak in crayfish Orconectes propinquus linked to Saprolegnia australis in Big Muskellunge Lake, Wisconsin

Crayfish populations in the area of the North Temperate Lakes Long Term Ecological Research (LTER) project, Wisconsin, USA, have been monitored for >25 yr. In 2005, native crayfish Orconectes propinquus from Big Muskellunge Lake were found with ulcerated lesions in the cuticle. In 2006, lesions occurred in 9.5% of sampled crayfish from the lake (n=3146). Ulcers generally occurred on the appendages of affected individuals but varied in location and severity. The prevalence of ulcers varied widely among sites, sample depths, and sampling dates, ranging from < 2% to >20%. The prevalence of ulcers in crayfish increased from a minimum in early June to a maximum in late July and August. In aquarium trials, healthy crayfish representing either O. propinquus or O. rusticus co-housed with ulcerated crayfish did not develop ulcers within 4 wk of exposure. Gross and histopathologic analyses of ulcerated crayfish revealed the presence of filamentous hyphae in the lesions while hemocytic infiltrates, melanotic reactions and silver-stained sections indicated that the ulcers had an oomycete etiology. Excised samples of ulcerated crayfish cuticle grown in culture developed an oomycete that was identified as Saprolegnia australis by PCR amplification and sequence analysis of 2 different DNA fragments. This is the first report of the occurrence of ulcers in wild crayfish associated with S. australis infection in the U.S.A. The advent of the outbreak and its underlying ecological causes are still under investigation.

Could native predators help to control invasive fishes? Microcosm experiments with the Neotropical characid, Brycon orbignyanus

Abstract – The potential of the native characid, Brycon orbignyanus, to help to control some invasive fish species currently present in the Paraná River basin was addressed through microcosm experiments. Juveniles of three invasive (Cichla piquiti, Oreochromis niloticus and Ictalurus punctatus) and two native (Astyanax altiparanae and Prochilodus lineatus) fish species were offered as prey to B. orbignyanus in 300‐l aquarium trials with three habitat complexity treatments (0%, 50% and 100% structure). Prey survival was much more variable among species (I. punctatus &lt; C. piquiti &lt; O. niloticus∼P. lineatus∼A. altiparanae) than through time, and B. orbignyanus predation was clearly mediated by habitat complexity, with lower prey survival in low‐complexity treatments. The lower survival observed for C. piquiti could be partially explained by its less active behaviour and its preference for a surface microhabitat and less structured areas. Prey size also affected predation rates, as for the three less consumed species the largest individuals were significantly preyed on. Our results suggest that preserving and restoring the populations of B. orbignyanus might help to control some fish species introduced to the Paraná River basin, particularly I. punctatus and C. piquiti.

Influence of prey body characteristics and performance on predator selection

At the time of settlement to the reef environment, coral reef fishes differ in a number of characteristics that may influence their survival during a predatory encounter. This study investigated the selective nature of predation by both a multi-species predator pool, and a single common predator (Pseudochromis fuscus), on the reef fish, Pomacentrus amboinensis. The study focused on the early post-settlement period of P. amboinensis, when mortality, and hence selection, is known to be highest. Correlations between nine different measures of body condition/performance were examined at the time of settlement, in order to elucidate the relationships between different traits. Single-predator (P. fuscus) choice trials were conducted in 57.4-l aquaria with respect to three different prey characteristics [standard length (SL), body weight and burst swimming speed], whilst multi-species trials were conducted on open patch reefs, manipulating prey body weight only. Relationships between the nine measures of condition/performance were generally poor, with the strongest correlations occurring between the morphological measures and within the performance measures. During aquaria trials, P. fuscus was found to be selective with respect to prey SL only, with larger individuals being selected significantly more often. Multi-species predator communities, however, were selective with respect to prey body weight, with heavier individuals being selected significantly more often than their lighter counterparts. Our results suggest that under controlled conditions, body length may be the most important prey characteristic influencing prey survival during predatory encounters with P. fuscus. In such cases, larger prey size may actually be a distinct disadvantage to survival. However, these relationships appear to be more complex under natural conditions, where the expression of prey characteristics, the selectivity fields of a number of different predators, their relative abundance, and the action of external environmental characteristics, may all influence which individuals survive.

Assessment of an underwater biopsy probe for collecting teleost fish tissue samples

This study tested the efficiency of an underwater biopsy probe designed to remove tissue samples for molecular analysis from small- to medium-sized (15 to 70 cm) marine teleost fish in the field. The probe was fired at lower and higher power from a 76 cm rubber-propelled spear gun. Two species were targeted: Plectropomus maculatus and Lutjanus carponotatus. The results were highly successful for P. maculatus, with >80% of hits at lower and higher power resulting in sufficient tissue extraction for molecular analysis. The results were less consistent for L. carponotatus at lower power (45%) due to the relatively large scales of the fish. At higher power the success rate increased to 73%. In 97% of cases, fish swam away rapidly with only minor lesions and showing no signs of incapacitation. Furthermore, aquarium trials showed no post-impact mortality after a 2 wk period. Therefore, the biopsy probe tested in this study is considered successful when the spear gun is fired at the correct power for the target species. This will allow for easier tissue sample collection from small- to medium-sized teleost fish for population and phylogenetic studies than previous methods of killing or capturing individuals.

A two-chambered trap reduces within-trap predation by octopus on rock lobsters in aquarium trials

A two-chambered lobster trap was developed that in aquarium trials significantly ( p < 0.01) reduced octopus predation on trap-caught spiny lobster. The trap was designed using information gained from an investigation of the behavioural interactions of the maori octopus ( Octopus maorum) with traps used in the South Australian commercial lobster ( Jasus edwardsii) fishery. This study showed that octopuses were primarily attracted to traps by the presence of bait as opposed to lobsters and that octopus entry into traps was ‘fortuitous’ and mediated by speculative exploration. The outer chamber of the modified trap contained bait and allowed entry by octopuses but not lobster and the inner chamber allowed access to both animals. The trap worked on the principle that octopuses would enter the outer chamber containing bait via a side entrance in preference to entry to the inner chamber containing lobsters via the neck. This was found to be the case and lobster mortality was 70% lower in the two-chambered trap than a standard trap. Successful adaptation of this trap design to commercial fishing conditions could significantly reduce rates of octopus predation on rock lobsters in several important southern hemisphere fisheries for spiny lobsters.