Save Our Sea Bass, by Don Orth

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Several years ago, I was at a conference in Queens, New York, and a group of us had dinner at a local restaurant.  It was an education conference and I was the only fisheries person in the group.  While scanning the menu, I noticed a seafood entrée, called Branzino.  Few things are more embarrassing than the fish guy being confused by an unfamiliar fish on a menu.  Someone asked, “What’s branzino?” So I replied, “I don’t know, but I’m ordering it.”   A smartphone search started.  It turns out that Branzino is an Italian name for the European Sea Bass Dicentrachus labrax, a member of the Moronidae family.  That’s the same family of the Atlantic Striped Bass Morone saxatilis, or Rockfish, so I knew this fish would be good.     

European Sea Bass Dicentrarchus labrax  from 21food.com

  The European Sea Bass is second only to the Atlantic Salmon Salmo salar, as the most popular food fish in Europe and occurs in the Mediterranean Sea and eastern Atlantic Ocean.  In Ancient Greece, it was said to be the “smartest of all fish, as it was the most difficult to catch.” However, today, in modern Greece, it is so rare to catch one that there is an expression “I caught a Sea Bass” (epyasa Lavraki) that roughly translates as “I hit the jackpot”.   So how did I hit the jackpot and order a European Sea Bass in Queens?

 

Grilled Branzino.   source:  www.poormansfeast.com

A popular food fish in the Mediterranean would have been overexploited many decades ago were it not for fishing regulations.  In the case of the European Sea Bass, regulations are not yet fully in place yet.  Fishing mortality has been increasing and abundance declining for at least 10 years.  Usually, a fishery goes through predictable phases if harvests are not regulated; these are: (1) predevelopment, (2) growth, (3) full exploitation, (4) over-exploitation, eventually (5) collapse, and hopefully (6) recovery.   

Sevel phases of fishery development. (Source:  FAO.org)

 Popularized by celebrity chefs, the catches of European Sea Bass are now at a 20-year low and ICES (International Council for the Exploration of the Seas) asked EU fishermen to reduce harvest by 80% to help revive the Sea Bass stock!  In 2015, the EU banned trawling during the spawning season to reduce harvest on Sea Bass; this was an emergency measure because the EU countries could not agree on harvest restrictions.  The fishery for wild European Sea Bass is reaching the collapse phase because regulations are not working.    

Consequently, non-profit organizations developed a public relations campaign to “Save Our Sea Bass.”   Organizations are primarily composed of the coastal sport fishers, who have the most to lose in this conflict.  Most recreational anglers in Europe release much of their catch, and this applies to European Sea Bass where 77% of marine anglers in England released their catch (Ferter et al. 2013).  Marine anglers from eastern and southern European countries are often more consumption oriented.  There are no studies of post-release mortalities of European Sea Bass, so it is difficult to know how effective minimum size limits might be.  After many years of conflict, the EU Commission persuaded the EU Member States to agree to a number of emergency measures to restrict harvests of Sea Bass. This campaign was supported by the "other B.A.S.S."  (Bass Angler’s SportfishingSociety). 

Commercial harvest of European Sea Bass.  Source.

European Sea Bass are eurythermic (5-28 °C) and euryhaline (3‰ to full strength sea water) and frequent coastal inshore waters, and occur in estuaries and brackish lagoons.  They are voracious predators on crustaceans, mollusks, and fishes.  Historically, they were raised in seawater ponds and lagoons where special barriers were placed in appropriate lagoon sites to capture fish before out-migration.  By the 1970s, mass-production techniques for juvenile Sea Bass were developed in most Mediterranean countries such that hundreds of thousands of larvae could be produced.  Thus, intensive aquaculture in sea cages became feasible and the production of sea bass greatly increased.  Today, prices for wild Sea Bass are much higher than farmed Sea Bass.   Most of the production occurs in Turkey, Greece, and Spain and the market is saturated.   Farmed production now dwarfs the wild capture fisheries.   Some efforts have begun to diversify the market through organic aquaculture.  

Farmed or Wild?  What’s the difference?  Farmed Sea Bass are cheaper.  But use of antibiotics and development of antibiotic resistance by pathogenic bacteria is a clear human health risk and no safe residue levels are established for most antibiotics.   The market demand for the more expensive wild Sea Bass far outstrips the sustainable harvest.    Therefore, the most likely source of my restaurant Branzino was farmed.   A recent ICES call for reduction in harvest means the wild fish will become even rarer – however, commercial fishers have resisted quota reductions for years.  Although the farmed Sea Bass production continues to rise, there are risks of intensive farming.  Risks include transfer of pathogens and genetic mixing between wild and farmed animals upon the escape of farmed sea bass from sea cages.

Wild Sea Bass stocks are at historic lows and emergency measures (ban on pelagic trawling, bag limit, closed areas and increased minimum size limits) are in place to reduce harvest by both commercial and recreational harvesters.  Size limits, such as a higher minimum landing size, appear to be a long overdue management strategy in order to avoid overfishing. The current minimum landing size of 36 cm (=14 inches) is below the size at which female Sea Bass reach sexual maturity (40-45cm).   This minimum landing size “corresponds with the size Sea Bass the market traditionally prefers” (Clover 2006; p 278), and not a size limit appropriate to conserve Sea Bass.

 

Number of offspring produced by different sized European Sea Bass.  Source.

Gear and area restrictions are also likely long-term management strategies debated.  A Sea Bass caught with hook and line provides the best quality flesh, relative to trawls, seines, or gill nets.   Fisheries based on line-caught Sea Bass would provide both the most jobs and highest price per kg of bass, while also being the least damaging to the marine environment. Discarding undersized Sea Bass is a significant issue for any fishing gear, other than hook and line.  Finally, gear and area restrictions are needed to prevent commercial fleets from targeting immature fish in nursery areas. 

I did not hit the jackpot with the Branzino I ordered in that Queen’s restaurant.  It was the result of decades of research and development to create an intensive sea-cage fish farming industry.   While the farmed production of European Sea Bass has grown, the harvest of Wild Sea Bass has dwindled as commercial and recreational interests from competing European states argue over appropriate fishing regulations. Let’s hope they act soon to Save Our Sea Bass.   

References

Clover, C.  2004. The End of the Line: How Overfishing Is Changing the World and What We Eat. London: Ebury Press.

Ferter, K. and sixteen coauthors. 2013. Unexpectedly high catch-and-release rates in European marine recreational fisheries: implications for science and management.  ICES Journal of Marine Science doi: 10.1093/icesjms/fst104   

Hillin, J., I. Coscia, and F. Volckaert.  2014.  European sea bass (Dicentrarchus labrax L). AquaTrace Species Leaflet. 

Perdikaris, C., and I. Paschos. 2010. Organic aquaculture in Greece: a brief review. Reviews in Aquaculture 2:102-105 

Ramirez, B., L. Ortega, D. Montero, F. Tuya, and R. Haroun.  2015.  Monitoring a massive escape of European Sea Bass (Dicentrarchus labrax) at an Oceanic Island: potential species establishment. Journal of Aquaculture Research and Development 6(5):339. doi: 10.4172/2155-9546.1000339

Sánchez Vázquez, F.J., and J.A. Muñoz-Cueto.  2014.  Biology of European Sea Bass. CRC Press. 436 pp.

On the Life of Kelly J. Meyer, by Don Orth

On October 24th I posted birthday wishes to Kelly Meyer on Facebook.  I sent him a photo of a Brook Trout for his birthday wishes. It was my last communication with him.   On the evening of November 4th, he died unexpectedly (see obituary), and, as is typical, I grasped for words to comfort his wife, Denise, and sons, Jack and Andrew, who I never knew, never met.  No words would come, only sadness.   Kelly was one of my graduate students from 1988 to 1990.  His life (vita from this 1990 MS thesis appears below) during his years at Virginia Tech remain among my fond, faded memories.  

During his time as a graduate student, Kelly studied the bioenergetics of Brook Trout (Salvelinus fontinalis) in streams of the Shenandoah National Park.  These unproductive, small streams are lined with dense Rhododendron and trout cannot move to find more suitable habitats during most seasons.   Brook Trout have adapted to these southern highland streams.  Kelly's thesis project explored the relation between the energy available in drifting insect prey and growth and consumption of brook trout.  The field work required sampling every six hours, flushing out stomach contents with lavage, and quantifying the mass of all items in stomachs and in the drift.  The waterproof, Ryan J (chart recording) thermograph recorded water temperatures continuously in this pre-digital era. The field work was strenuous enough just to hike into the study areas. Once there, you realized just how mal-adapted bipedal hominids are for wading these streams.  Few investigators have attempted this type of work, especially over the 24-hour cycle.  Kelly was interested in the challenge and was attracted to studying native Brook Trout in their natural habitats.    While in the Peace Corps, stationed in Lesotho, in southern Africa, Kelly managed to apply his skill set to survey isolated populations of the critically endangered Maloti Minnow Pseudobarbus quathlambae.  This minnow is still struggling to persist today (see recent story).

A mountain stream of Virginia and home to the native Brook Trout.

Kelly's thesis findings are significant to the survival and persistence of Brook Trout.   The southern strain of Brook Trout are adapted to life in the small, infertile mountain streams but growth rates can be very slow and adult body size is modest.   In some streams, the amount of energy Brook Trout could assimilate was barely enough to meet their standard metabolic needs, much less to permit energy for activity or growth.  Very few mountain streams provide the right combination of habitats and food.

Differences between assimilated and maintenance energy for Brook Trout in four study streams in Shenandoah National Park (Meyer 1990).

Consequently, it is the rare Brook Trout that captures sufficient prey and meets energetic needs to live and swim and grow large enough to produce mature eggs and contribute to the next generation.   Brook Trout in these mountain streams continuously monitor the available drifting insects and dart out to capture the larger, more energetically valuable prey. The best streams have an abundant canopy to shade the stream and keep water cool enough for optimum Brook Trout feeding (12-17°C).   The optimal Brook Trout streams also produce an abundant and diverse fauna of invertebrates, including aquatic and terrestrial forms.   Kelly's hypothesis that growth and consumption of Brook Trout was influenced by abundance of larger prey in the drift was supported by his field studies (see below), especially within streams.   He also identified an energy minimizing strategy by the Brook Trout that enabled them to reduce activity costs when prey levels were low.  Years later, Railsback and Rose (1999) confirmed that  growth of Rainbow Trout was strongly influenced by factors controlling food consumption.  Their work and most other more recent field investigations relied on model-estimated food consumption rather than diel sampling.  

Percent of consumption captured by Brook Trout in relation to density of large drifting prey (Meyer 1990)

One of the surprises in the study was the regular appearance Gypsy Moth (Lymatria dispar)  larvae in the guts of the Brook Trout.   Gypsy Moths are a devastating forest pest that feed on foliage and were marching through the Appalachian mountains at that time.   The pest has been in North American for 100 years. A major concern is the potential loss of economically critical and ecologically dominant oak (Quercus spp.) trees.  Yet, the examination of the diet demonstrated that this terrestrial pest was subsiding the Brook Trout in these forest-covered mountain streams.

Realizing the practical difficulties for numerous intensive field investigations, Kelly Meyer also developed an energetics-based model to analyze dynamics of trout populations in Appalachian streams.  The model included mathematical formulations for temperature effects, size-dependent mortality, seasonal mortality to predict population changes and  average trout size.  The model was programmed in the language of the times (FORTRAN).   These calculations are essential components to define the thermal niche of the Brook Trout.  They may be used in future efforts to project the effects of climate change on suitability of streams for Brook Trout in the southern Appalachian mountains.  Many partners are involved via the Eastern Brook Trout Joint Venture, to protect, restore, and enhance remaining Brook Trout 

Most of Kelly's fisheries career was with the White Mountain Apache Tribe Game and Fish Department and  Arizona Department of Game and Fish.  When he was first hired, he was the only fisheries biologist with the White Mountain Apache Tribe; he would joke that he was Chief of Fisheries.  In this role, his expertise was critical in the management and recovery of the federally endangered Apache Trout (Oncorhynchus apache).  Many actions are required for the recovery of  Apache Trout and the success of recovery depends on special people, such as Kelly Meyer, who possess the patience and skills to work with the many cooperators to set appropriate fishing regulations, improve stream habitats, negotiate agreements, install and maintain barriers, and prevent movements of non-native competitors.  He was a field scientist for all seasons and for all peoples.  We need more people like Kelly Meyer in this world.   I am very saddened with news of his passing.

REST IN PEACE

Kelly J. Meyer

1961-2015

References
Meyer, K. J. 1990.  Effects of drifting prey abundance on food consumption and growth of brook trout in Shenandoah National Park.  Master's Thesis. Virginia Polytechnic Institute and State University, Blacksburg, Virginia.  111 pp.
Meyer, K.J., and D.J. Orth.  1990.  Development and application of an energetics-based model for trout populations in Appalachian streams.  Final Report, U.S.D.A. Forest Service, Southern Forest Experiment Station. 129 pp.
Railsback, S.F., and K.A. Rose. 1999.  Bioenergetic modeling of stream trout growth: temperature and food consumption effects.  Transactions of the American Fisheries Society  128:241-256.

Trout-perch: Is it a trout? Or a perch? or Neither? by Don Orth

The Trout-perch Percopsis omiscomaycus (Walbaum) is a widely distributed species in North America, yet they present a number of puzzles.  Percopsis means “perch like” (Greek, perke=perch and opsis=appearance) and omiscomaycus is an Algonkian name that includes the root word “trout.” This enigmatic fish is certainly not a trout – though it has an adipose fin and a scaleless head --  and certainly not a perch – though its coloration and spines are somewhat similar.   It has traits that are characteristic of each group.  For example, the dorsal fin has 2 weak spines and pelvic and anal fins each have one weak spine. And the scales are ctenoid with a single row of teeth on the edge.  But, there is that puzzling adipose fin.   The head is large and the premaxillary bones are nonprotractile, unlike the Yellow Perch Perca flavescens.  Trout-perch are ray-finned fish in the Class Actinopterygii (ACK-tih-NOP-tuh-RIJ-ee-eye).  They are a surviving remnant of mostly marine fish that marked the transition between soft-rayed and spiny-rayed fishes. They belong to a superorder called Paracanthopterygii (literally "like" spiny rays) and Trout-perch are the only fish in that group with an adipose fin.   

Trout-perch Percopsis omiscomaycus (Walbaum) Illustration by Ellen Edmonson  Source

Phylogeny of trout perch is just plain confusing because they possess a primitive trait, the presence of adipose fin, but many other derived traits.   This is likely an example of character reversal, where the adipose fin (the ancestral trait) reappears during the evolution of the lineage.  The genus Percopsis is  taxonomically very distinctive. There are two species, the Sand Roller Percopsis transmontana,  ranges from western Idaho in the lower Snake River westward through the lower Columbia and Willamette drainages.     Recently Thomas Near and colleagues estimated, after analyses of DNA sequences from 232 fish species, that divergence of trout-perches from marine relatives, such as deep-sea beardfishes, Polymixiidae, and cods, Gadiformes, began over 100 million years ago.  The closest extant relatives include the cavefishes, Amblyopsidae, and Pirate Perch, Aphredoderidae in the order Percopsiformes.  Although these relatives have external characteristics that are very different from Trout-perch, they are classified together due to internal similarities. All members of the Percopsiformes are freshwater fishes, but the group appears to have a marine origin.

The distribution ranges widely from north to south in deep lakes as well as large streams. Trout-perch are currently found from the Missouri River drainage east to the Connecticut River, south to the Potomac, and from the Ohio River north throughout the Red, Saskatchewan, Mackenzie, and Yukon Rivers to the north.  Following the last glacial age, the Trout-perch probably moved from the lower Mississippi valley into newly thawed water bodies as glaciers retreated northward. Despite this broad distribution and locally high abundance, there is seemingly little known about this small-bodied benthic fish. 

Range of the Trout-perch (Becker 2001)

What do they eat?  Trout-perch consume a variety of benthic animals, depending on their habitat.  The are nocturnal feedings and move inshore to feed.  Most common diet items include Chironomidae larvae, Hexagenia nymphs, amphipods, Cladocera, and  Copepoda.  Trout-perch are seldom captured in daytime shoreline seining even in waters where it is abundant.  They appear to move inshore at night to feed.  In the Great Lakes, they overlap with Ruff Gymnocephalus cernua and Yellow Perch Perca flavescens, juvenile Walleye Sander vitreus, and Round Goby Neogobius melanostomus.   Trout-perch diet preferences overlap with Yellow Perch and juvenile Walleye.   In Lake Erie, “trout-perch ingested benthic prey items in proportion to their availability in the environment” and Chironomidae, Hexagenia, Nematoda, Hirudinea, Amphipoda, and Trichoptera composed over 90% of benthic macroinvertebrates in the diet by number.  They appear to avoid competition with other fishes by using cooler areas of the lake. 

Near shore abundance trends in Lake Erie source (Kocovsky et al. 2014)

In Lake Michigan, native species (Emerald Shiner Notropis atherinoides, Lake Herring Coregonus artedi, and Deepwater Cisco Coregonus johannae) declined when Alewife Alosa pseudoharengus and Rainbow Smelt Osmerus mordax invaded; however, Trout-perch were seemingly not affected by the Alewife increase.  The Trout-perch is the most abundant fish in trawl samples from western Lake Erie (Kocovsky et al. 2014).  Through the multiple invasions of White Perch Morone americana, Quagga and Zebra mussels Dreissena spp., spiny waterflea Bythotrephes longimanus and Round Goby in Lake Erie, the  Trout-perch remains an abundant benthic invertivore.  

Growth curves (total length, mm, plotted against year of life) House and Wells (1973)

Trout-perch never grow very large (maximum length is only 13 cm).  Therefore, they are vulnerable to predation by many piscivores.   Trout-perch are eaten by many fishes, including the northern pike, burbot, yellow perch, walleye, freshwater drum.  However, they are not always a preferred prey and not always common in diets of Walleye or Lake Trout even where they overlap.  Why?   No one is sure.  They provide equivalent energy to soft-rayed fishes, yet walleye positively select soft-rayed fishes as prey (Knight et al. 1984; Hall and Rudstam 1999).   As a trophic link between benthic invertebrates and large lentic fish the abundant Trout-perch remain an enigmatic weak interactor.     

The Trout-perch will remain an enigma for some time.  However, students of Ichthyology will always appreciate this easy-to-identify small fish with a big head and an adipose fin.    It’s the only Percopsis in most regions and the genus, family and order names all have the same root.   They appear in many standardized fish trawl sampling programs and, therefore, a long-term record of abundance continues to accumulate.  

References
Becker, G.C. 2001.  Fishes of Wisconsin. University of Wisconsin Press, 1052 pp. 

Blouzdis, C.E., L.N. Ivan, S.A. Pathoven, C.R. Roswell, C.J. Foley, and T.O. Höök.  2013.  A trophic bottleneck?: The ecological role of trout-perch Percopsis omiscomaycus in Saginaw Bay, Lake Huron. Journal of Applied Ichthyology 29:416-424.

Hall, S.R., and L.G.Rudstam. 1999. Habitat use and recruitment:  comparison of long-term recruitment patterns among fish species in a shallow eutrophic lake, Oneida Lake, NY, U.S.A. Hydrobiologia 408/409: 101–113.

House, R., and L. Wells. 1973.  Age, growth, spawning season, and fecundity of the trout-perch (Percopsis omiscomaycus) in southeastern Lake Michigan.  Journal of the Fisheries Research Board of Canada 30:1221-1225.

Knight, R.L., Margraf, F.J., Carline, R.F., 1984. Piscivory by walleyes and yellow perch in western Lake Erie. Transactions of the American Fisheries Society 113, 677–693.

Kocovsky, P.M., A.T. Stoneman, and R.T. Kraus.  2014. Ecology and population status of Trout-perch (Percopsis omiscomaycus)in western Lake Erie.  Journal of Great Lakes Research 40:208-214.

Near, T.J., and eight coauthors. 2012.  Resolution of ray-finned fish phylogeny and timing of diversification.  Proceedings of the National Academy of Sciences of the USA 109(34):13698-13703. 

Life At the Water’s Surface: Brook Silverside Labidesthes sicculus by Don Orth

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I always enjoy observing fish, especially those that we can see from the surface.   One of these is the Brook Silverside, Labidesthes sicculus.  The fish would frustrate me during a phase when I was obsessed with quantifying fish numbers because these surface dwellers would easily jump over or swim through carefully anchored block nets (another violation of the closure assumption).   Brook Silverside is the most widespread member of the Atherinopsidae family in North America.  We pronounce the scientific name lah-beed-ess-theez  sick´-you-lus. The Atherinopsidae is the family of Neotropical Silversides that inhabit both marine and freshwaters of North, Central, and South America.  Based on fossil remains the family is of recent (Pliocene) origin.  There are 104 species in 13 genera in the Atherinopsidae.    Some silversides endemic to Mexico (Poblano spp.) are threatened species.  The most famous species are the California Grunnion, Leuresthes tenuis, Atlantic Silverside, Menidia menidia, and the Inland Silverside, Menidia beryllina.   These are small, very elongate fishes with body lengths 5-7 times the maximum body depth.   The silversides are small fishes and are important forage fish for all local piscivorous fishes.

Brook Silverside by Howard Jelks

The Brook Silverside species was described by Edward Drinker Cope  from a Michigan holotype in 1865. The genus name, Labidesthes was derived from the two words: labidos, forceps and esthio, eat.   It refers to the prolonged jaws, which form a short, depressed beak  (see photo). The species meaning of sicculus is less clear.   William Pflieger, in The Fishes of Missouri, interpreted Cope’s finding of specimens found in half-dried pools as meaning siccus (meaning dried).  Though this interpretation has been repeated in numerous subsequent references,  recently Christopher Sharf and Kenneth Lazaro explained that sicculus was more likely meant as an adjectival form of sicula, dagger, referring to the fish’s sharp snout and dagger-like shape.

The Brook Silverside is well camouflaged in near surface waters.  The fish, in life, is nearly transparent with pale shades of olive on the back and upper sides.   Dorsal scales are clearly outlined with melanophores.   A distinctive lateral silver band becomes broader in anterior portions and is underlain by black pigment.  Parts of the body, opercles, and underside of the head are silvery white with iridescent blue-green. Maximum size of the Brook Silverside is 11 cm (standard length). 

The range of Brook Silverside is usually described as Great Lakes region and south through the Mississippi Basin and Gulf Coastal Plain drainages.  Older references recognized a single species and an uncertainty over clinal variation or subspecies in Labidesthes.  However, Werneke and Armbruster (2015), after examining morphometric, meristic, and osteological data from numerous populations, concluded there are two valid species.   

“Labidesthes sicculus is found in Gulf of Mexico drainages from the Brazos River East to the Pascagoula River, Mississippi River (absent in middle and upper Missouri River), and Great Lakes-St. Lawrence River (absent in Lake Superior). Labidesthes vanhyningi is found in Gulf Mexico drainages from the Neches River East around peninsular Florida North on the Atlantic Coast to the Pee Dee River, in the Mississippi River it is confined to lowland areas of the Lower Mississippi River.”

 Labidesthes sicculus (top) and Labidesthes vanhyningi (bottom).  In Labidesthes sicculus note the midlateral silver band is narrowest on caudal peduncle, broadening and fading anteriorly whereas it is not tapering anterior of first dorsal in Labidesthes vanhyningi.  The ratio of thoracic length to abdominal length is longer in Labidesthes sicculus. (Werneke and Armbruster 2015)

“Brook” is actually a misnomer -- the Brook Silverside more frequently inhabits open areas of rivers, lowland streams, lakes and reservoirs and avoids fast current and shallow waters.  It is highly adapted for living right at the water surface.  Brook Silverside are most associated with waters with low turbidity and fairly clean substrates or deep waters in weedy lakes and rivers.    The often occur in very large aggregations and make inshore-offshore migrations in the large schools.  

The body form of the Brook Silversides reveals its habits.  The flattened head is often in direct contact with the surface film.    The large eye indicates a visual feeding mode.  The large, beak-like terminal mouth indicates a specialized, near-surface predator.  A short s-shaped gut lacking pyloric caeca, indicates a carnivore.  A quick acceleration and a snap of the jaw results in rapid prey capture.  Most diet studies confirm that Brook Silversides eat planktonic crustaceans, small flying insects, and immature insects, such as the phantom midge Chaoborus. 

Close up of head of Brook Silverside, by Uland Thomas

They are often seen jumping out of water in seeking flying insect prey.   One  prey includes the dance flies (Empididae), which frequently hover in large swarms just above the surface.  Alvin Cahn made extensive observations on Brook Silverside in southern Wisconsin lakes.  Cahn estimated that Brook Silverside spends "most of their time within ten or twelve centimeters of the surface…" and “never under any conditions descends below the upper meter of water…. while nothing can drive the immature individuals more than a few centimeters below the  surface."     They have periods of very intense activity during the day and Hubbs (1921) observed that “adults at night were observed to lie quiescent as though asleep."   However, Cahn later observed periods of intense activity at night during full moon.   This video of a Brook Silverside does not capture the periods of intense surface feeding of large schools.   

Many Brook Silversides live just 15-17 months as they die sometime after the one and only spawning.   Therefore, it is important that spawning times are synchronized to ensure reproductive success.  The moon phases may be important cues that initiate spawning activity in the Brook Silversides.   Brook Silverside breed in spring (May-June) in shallow waters along shore.   There is no clear sexual dimorphism; however, pairs of silversides are seen swimming near shores in pairs as temperatures warm to 18°C.   Cahn discovered that the upper fish in a pair is male, the lower female.  As temperatures warm further (20-22°C) this swimming speed increases until the fish are travel in fast spurts, and often breaking the water surface.  Spawning aggregations may include many male and females.   The distance between the pair approaches 5 cm as the females continue to dart “this way and that way,” pursued by a trailing male.  Eventually, the female slows darting pace and allows the male to approach her side. The pair then swims toward the bottom and make repeated contacts with their abdomens. During the descent eggs are extruded and immediately fertilized by the attending male.  The female is spent after completing a single breeding, while the male ascends to the surface to pursue other females.   The eggs have a single gelatinous filament about six times the egg diameter.   The filament firmly attaches to the first thing it contacts.     Eggs hatch in 8-9 days at 24°C and the young silversides "wiggle" in attempt to their attempt to reach the water surface. 

Grier and his colleagues studied the Brook Silverside when ripe and stripped eggs from females with gentle pressure on the abdomen.  When they did this they observed many embryos with well-developed, pigmented eyes!    They only way for this to happen is if eggs were internally fertilized.  This is not what Alvin Cahn described.  Grier confirmed this via histological examination that revealed both sperm and developing embryos in the ovaries. Further observations revealed that the male Brook Silverside possesed a short genital palp immediately posterior to the anus, which presumably acts as an intromittent organ.  Therefore, the female Brook Silverside may release eggs, in different developmental stages, in open water or deposit them on aquatic vegetation and other substrates.

A) Scanning electron micrograph of ventral surface of male showing a short genital papilla;B) Ventral surface of female showing absence of a genital papilla. Grier et al. (1990).

Brook Silversides are not used as bait minnows – they are too fragile and thin bodied and do not survive well in bait buckets.  Similarly, they do not adapt readily to life in aquaria.   They are eaten by many piscivores, including Longnose Gar, Bowfin, Cisco, Yellow Perch, Smallmouth Bass, Largemouth Bass, Northern Pike, and sunfish.  But their small size (1-2 g) means large piscivores will not waste their time.  Water snakes, mudpuppies, and turtles are also likely to eat them.

The Brook Silverside is introduced to other waters via constructed canals or intentional introductions as prey fish.  For example, they were introduced as supplemental prey in Kentucky lakes in the 1960s.   Dams and industrial and agricultural pollution have extirpated many local populations.   Also, the Inland Silverside Menidia beryllina (synomous with Mississippi Silverside Menidia audens) was widely introduced as a prey fish in newly constructed reservoirs. Also, the non-native Inland Silverside was likely introduced to the Tennessee-Ohio River system via the Tennessee-Tombigbee Waterway, which connects Gulf Coast drainages to the lower Tennessee River.  Brook Silverside is virtually undetectable in reservoir electrofishing surveys after 14 years of co-occurrence with Inland Silverside. Declines in Brook Silverside were also observed in several other reservoirs after introduction of the Inland Silverside. 

Increase in abundance of the Mississipi Silverside (top) and concurrent decline in the Brook Silverside (bottom) in Tennessee River reservoirs from Simmons (2013).

The Brook Silveside is an excellent representative of life in the near-surface zone.  The large schools are fun to watch, especially the intense feeding and jumping to capture prey.   Only during breeding does the Brook Silverside experience life away from the water’s surface.    A most surprising finding was the discovery of internal fertilization in the Brook Silverside 125 years after the species was discovered.  Fascinating!

References

Cahn, A. R. 1927. An ecological study of southern Wisconsinfishes. The brook silversides (Labidesthes sicculus) and the cisco (Leucichthysartedi) in their relations to the regions. Illinois Biological Monographs 11(1):1-151.

Cope, E.D.  1865. Partial catalogue of the cold-blooded vertebrata of Michigan. Proceedings of the Academy of Natural Sciences of Philadelphia  17:78–88.
Grier, H.J., D.P. Moody; and B.C. Cowell. 1990. Internal fertilization and sperm morphology in the brook silverside, Labidesthes sicculus (Cope). Copeia 1990(1):221-226.
Hubbs, C. L. 1921. An ecological study of the life-history of the fresh-water atherine fish Labidesthes sicculus. Ecology 2(4):262-276.
Keast, A., and D. Webb. 1966. Mouth and body form relative to feeding ecology in the fish fauna of small lake, Lake Opinicon, Ontario. Journal of the Fisheries Research Board of Canada 23(12):1845-1874.
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