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PhysOrg

Male cod may ‘sing’ to females during mating, suggests a new study investigating the sounds cod and pollack produce during the spawning season.

The research, published in the Journal of Fish Biology, aimed to learn more about these noises, and why the fish make them. They discovered that the grunts were produced in rhythmic patterns, suggesting that the females in the shoal may use these rhythms to choose a mate.

To investigate the noises, the team studied two populations of fish in tanks at a fishery in Scotland. Cod, had previously been recorded making grunting noises as they got ready to spawn, but the pollack’s grunt had never been recorded until now. You can hear the grunts produced in the recordings on this page.

‘We already knew male cod produce these sounds, we just wanted to dig a bit deeper, and find out if the sound changed over time to indicate that a spawning event might be occurring. But it was really exciting to find pollack also produce these sounds,’ says Lindsay Wilson, a NERC-funded PhD student at the Scottish Association for Marine Science (SAMS) who led the research.

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South China Morning Post

Escalating carbon dioxide emissions will cause fish to lose their fear of predators, potentially damaging the entire marine food chain, joint Australian and US research has found.

A study by the Australian Institute of Marine Science (Aims), James Cook University and the Georgia Institute of Technology found the behaviour of fish would be “seriously affected” by greater exposure to CO 2.

Researchers studied the behaviour of coral-reef fish at naturally occurring CO 2 vents in Milne Bay, in eastern Papua New Guinea.

They found that fish living near the vents, where bubbles of CO 2 seeped into the water, “were attracted to predator odour, did not distinguish between odours of different habitats, and exhibited bolder behaviour than fish from control reefs”.

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The Columbia Basin Bulletin

A study of 91 stream restoration projects in the lower Columbia River and Oregon coastal river basins that added wood to increase pool complexity and pool surface area — better habitat for juvenile coho salmon — found that after six years most of the projects had increased over-wintering rearing capacity for the salmon.
 
The restoration projects placed large logs in small to medium sized streams that had been damaged by years of neglect and that had lost much of the natural stream’s complexity of pools and gravel. The projects’ design was to use wood without cabling to hold them in place in areas that would be expected in a natural stream. After six years of monitoring, biologists saw an increase in the surface area of pools and an increase in gravel.
 
However, the amount of large wood that had been installed declined over the six years in almost 75 percent of the projects and few sites collected new wood. But even with this decline, wood remained on average 100 percent of the pretreatment levels of wood.
 
In addition, changes in channel complexity and flood plain connectivity, the more wholistic and desired outcomes of the projects, were not observed.

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The Columbia Basin Bulletin

Juvenile wild steelhead are smaller than hatchery fish when they reach the ocean, but have a higher feeding success, are in better condition and grow faster than hatchery fish once they arrive in the marine environment, according to a recent study.
 
“Juvenile steelhead enter the marine environment each year at a similar size and condition, yet after a short period in the marine environment, they are feeding and growing at a much higher rate than in the estuary as they quickly move offshore and this growth depends on ocean conditions,” said Elizabeth A. Daly, senior faculty research assistant for the Cooperative Institute for Marine Resource Studies (Oregon State University and NOAA Fisheries), which is located at the Hatfield Marine Science Center in Newport, Ore.
 
The Bonneville Power Administration since 1998 has funded NOAA and CIMRS/OSU on an ongoing ocean research project on juvenile salmon marine survival.
 
The study measured and weighed both wild (unmarked fish) and hatchery juvenile steelhead in the Columbia River estuary and in the ocean. According to the report, wild steelhead were slightly shorter than hatchery fish as they entered the ocean, but were overall healthier, fed with greater success and grew faster than the hatchery juveniles.

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Livescience

The Mexican blind cavefish does not have eyes, but it can “see” obstacles in dark caves by puckering its mouth and producing bursts of suction, according to a new study. The research describes this unique form of navigation for the first time.

Scientists previously thought the eye-less Mexican cavefish navigated by sensing changes in water pressure produced by waves sent off from the fish’s own body. But when the researchers examined the fish, they found some problems with this explanation. For example, larger fish, which would presumably produce larger waves, should be able to identify objects from farther away than smaller fish. In fact, larger fish detected objects at about the same distance as smaller fish did.

Researchers at Tel Aviv University in Israel decided to investigate the sightless navigation further, conducting an experiment in which they counted the number of times the fish opened and closed their mouths when near objects the fish were familiar with. The researchers then moved the objects and observed changes in the fishes’ mouth movement in the unfamiliar environment.

The fish opened and closed their mouths more than twice as frequently in unfamiliar surroundings, and more frequently when approaching an object than in the open, with no objects nearby, suggesting this behavior plays a role in detecting the fish’s environment.

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FIS

A team of researchers from the Institute of Marine Sciences (ICM) discovered a new hormonal mechanism that controls the formation of spermatozoa in fish.

According to Joan Cerdà, initiative leader and researcher at the Institute of Agrifood Research and Technology (IRTA) of the Higher Council for Scientific Research (CSIC), this finding could help clear up the mystery about the causes of male infertility in fish.

The authors of this research, whose results were recently published in the journal Proceedings of the National Academy of Sciences (PNAS), focused on studying the causes of infertility of Senegalese sole males bred in captivity.

One of the hypothesis to explain this is that this is an epigenetic problem during larval development due to a still undetermined cause.

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Science Codex

A new study showed that several Gulf of Mexico fish embryos developed serious defects in heart development following exposure to crude oil from the Deepwater Horizon oil spill. The study is the first to analyze the effects of the primary toxic agents released from crude oil on several commercially important pelagic fish species that spawn in the Gulf of Mexico.

The research team, which included five researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, concluded that, “losses of early life stages were therefore likely for Gulf populations of tunas, amberjack, swordfish, billfish, and other large predators that spawned in oiled surface habitats.”

“This study is the first to understand the impacts of the Deepwater Horizon oil spill on the early life development of commercially important fish in the Gulf of Mexico,” said Daniel Benetti, UM Rosenstiel School professor of marine affairs and policy and director of the Aquaculture Program. “The findings can be applied to fisheries management questions in marine regions where crude oil extraction is prevalent.”

The study, published in the March 25 issue in the journal of the Proceedings of the National Academy of Sciences (PNAS), assessed the impacts of polycyclic aromatic hydrocarbons (PAHs), a toxic agent released from crude oil, from Deepwater Horizon oil samples on embryos of bluefin tuna, yellowfin tuna, and amberjack. Embryos were exposed to two different oil samples, one collected from surface skimming operations in the Gulf of Mexico and another from the source pipe attached to the damaged Deepwater Horizon wellhead.

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Proceedings of the Royal Society

We describe the bi-directed eyes of a mesopelagic teleost fish, Rhynchohyalus natalensis, that possesses an extensive lateral diverticulum to each tubular eye. Each diverticulum contains a mirror that focuses light from the ventro-lateral visual field. This species can thereby visualize both downwelling sunlight and bioluminescence over a wide field of view. Modelling shows that the mirror is very likely to be capable of producing a bright, well focused image. After Dolichopteryx longipes, this is only the second description of an eye in a vertebrate having both reflective and refractive optics. Although superficially similar, the optics of the diverticular eyes of these two species of fish differ in some important respects. Firstly, the reflective crystals in the D. longipes mirror are derived from a tapetum within the retinal pigment epithelium, whereas in R. natalensis they develop from the choroidal argentea. Secondly, in D. longipes the angle of the reflective crystals varies depending on their position within the mirror, forming a Fresnel-type reflector, but in R. natalensis the crystals are orientated almost parallel to the mirror’s surface and image formation is dependent on the gross morphology of the diverticular mirror. Two remarkably different developmental solutions have thus evolved in these two closely related species of opisthoproctid teleosts to extend the restricted visual field of a tubular eye and provide a well-focused image with reflective optics.

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The Scientist

Plucking older, more experienced fish from a migratory school may impair the group’s ability to migrate successfully to feeding grounds, according to a study published today (March 18) in the Journal of the Royal Society Interface.

A team of fisheries biologists and biophysicists developed a mathematical model to decipher how fish navigate, finding evidence to suggest that information about migration sites is stored in the memories of knowledgeable fish. This theoretical result serves to strengthen anecdotal evidence that how fish learn from one another is crucial for maintaining healthy migrating populations.

“When we try to understand natural populations, studying these systems with mathematical models is a very powerful tool to use,” said Colin Torney, a mathematician with the University of Exeter in the U.K., who studies animal ecology but was not involved in this work.

Most mathematical models of marine animal behavior rely on representations of spatial interactions among individuals—for example, how fish behave in relation to others near them. Researchers led by Matteo Marsili of the Abdus Salam International Centre for Theoretical Physics in Trieste, Italy, however, developed a model that relies on stochastic adaptive networks, which they used to study the probabilities of interactions among fish.

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Wyoming Public Media

A study by several University of Wyoming researchers on salmon spawning in the Pacific Northwest could help pacific fish populations as well as Wyoming trout numbers. Clifford Riebe is an assistant professor in UW’s Geology Department and helped author the study.

The report says certain kinds of riverbeds help salmon spawning and since trout and salmon are closely related Riebe says managers in both areas could use the data to grow fish populations.

Clifford Riebe said “a manager could then figure out using our model they could figure out how much of the bed is usable for that particular fish. And it should work for any fish that spawn in the same way as the pacific salmon that we studied in our work. And this is generally true of the trout that we find in Wyoming.”

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