Wednesday, June 15, 2016

The Common but Captivating Carp (Cyprinus carpio)

Common carp (Cyprinus carpio) were introduced to the US in the 1800's as a fast growing, highly adaptable food fish for the masses, but the enthusiasm for carp has since turned into disdain. They remain popular in their native Europe and Asia but in America they are now thought of as a nuisance, or technically a "non-native non-game species"; meaning carp are unwanted as food or sport. Carp gained blame and a reputation (undeserved) for degrading water quality by stirring sediment as well as the decline of game fishes by eating their eggs. Carp indeed forage in the mud and stir up, mainly because of their fondness for the aquatic vegetation in these areas. But carp are strongly associated with muddy, non-productive (from a fisherman's perspective) waters because: #1 they are often literally seen in the shallows and other fishes are not, and #2 they can thrive in conditions most species cannot, leading people to believe carp have elbowed out other fishes and muddied the waters. In fact carp are simply able to thrive where other fishes cannot.

Carp have fleshy sucker mouths for digging in substrate for food and barbels to "smell" for food

One of our exhibit carp has an irregular scale pattern
The irony of carp being thought of as the definitive "trash fish" is that their better known - literally mutant - version of carp is the koi; a fish that is revered, bred, painted, tattooed, kept as pets, and even sold for tens of thousands of dollars. The truth is that carp in any form are tough, smart and quite beautiful. Wild common carp show natural variations, which led to their breeding to the koi variety that can be seen in local waters; irregular scale patterns, highly variable coloration, different body shapes, etc. We exhibit and raise wild local carp and appreciate their worth as an exhibit species and in our local waterways. Each spring we await their mini-migration up tributaries of the James River that lead them right into the heart of the suburbs and the city limits. Carp spawn in very shallow vegetated water and can be seen gathering in mass in late April in our area. Several males follow a larger female and they spawn against vegetation, on which the female lays adhesive eggs. We collect roots and vegetation covered with fertilized carp eggs to raise and display and or release, as we don't really need any more carp here.

Adhesive eggs on vegetation
Carp fry attached to the glass
A juvenile carp, about 3 weeks old
Newborn carp fry attaching to the glass

The largest of the juvenile carp

We simply place the vegetation with eggs in a mesh bag with some current flowing on them, then we wait. The eggs hatch very quickly, usually within a few days, and the fry generally end up escaping the bag - or we open it - and attach to the sides of the tank. They stay attached for less than a week and feed upon artemia nauplii and powdered spirulina flakes. The differences in growth rates within a cohort is remarkable; some baby carp may be ten to twenty times the size of their siblings. Whether we release them or display them for a while, carp are fascinating fish. They are survivors that challenge our core ideas of what is worthwhile and why - and who decides it. Looks matter, commercial worth (tastiness to humans) matters, perception is reality (and often mistaken), and attitudes change over time. In the meantime, carp are going to be here rooting around in the mud, and we'll raise them just for fun.

Friday, June 10, 2016

Building an Artificial Oyster (Castle) Reef - part II

Several VLM staff members from three departments recently headed to Chincoteague over two day-long sessions in May to help the Nature Conservancy construct artificial oyster reefs out of concrete "castles". Staff and volunteers met at Chincoteague wild and beautiful USFWS National Wildlife Refuge on Virginia's Eastern Shore. The area is best known for its wild ponies that roam free amid the dunes and low grasslands adjacent to the Atlantic Coast. The shallow inlets within the refuge experience heavy tidal flow that provide rich waters and ideal conditions for oyster reefs.

Just a few of the many wild ponies that inhabit the island

These reefs are constructed of tiered concrete blocks that are designed to be stacked and interlocked vertically into a pyramid-like structure (see below). When these stacked blocks are oriented in a staggered horizontal line, they create a reef that acts as a breakwater to diffuse wave energy, trap sediment also allows plenty of hard surface for oyster spat to settle on preventing their possible burial.

 Before and after: First "castles" are left in piles in the inlet, then rearranged by volunteers into specific patterns, as well as long rows, for both stability and maximum oyster growth. 

A model of the castle configuration on dry land

Actually building the reef

 The "castles" had to be towed around when the water was high.

According to biotic surveys done on the reefs constructed last year with the assistance of the VLM aquarium staff, the reefs were deemed to be very successful and highly colonized, meaning lots of new oyster, fish, crabs and other inverts now call that reef home!

A clump of healthy oysters with plentiful algae

Fishes like this striped burrfish come to oyster reefs to feed on inverts

We have a live display of an artificial oyster reef on-site that exhibits live animals that inhabit healthy oyster reefs and provides information on the work being done by the Nature Conservancy and Christopher Newport University Professor Dr. Russ Burke. The efforts to provide a healthy habitat for wild oysters and the ever-growing oyster cultivation industry are helping to spur a slow but steady comeback by one of the Bay's iconic animals the American oyster.