» Posted by on Mar 11, 2016 in Blog, Chris F | Comments Off on Tridacna Clams for the Aquarium

Giant Clams of the Tridacna Genus

By: Christopher Fong

Tridacna gigasSeveral species of giant clams belonging to the family Tridacnidae enter the aquarium hobby regularly and are often sought after for their color and unique patterning. Each clam has their own distinct patterning making them different and unique even from another individual of the same species. The most common species include Tridacna maxima, Tridacna crocea, Tridacna squamosa, and Tridacna derasa. Other species exist but seldom enter the aquarium hobby such as the infamous Tridacna gigas which grow to weigh an impressive 550lbs and the exceptionally rare Tridacna mbalavuana commonly known as the devil clam. Most Tridacna clams are found within the tropical Indo-Pacific reef communities where local farm these beautiful creatures for food and for the aquarium trade. They can also be found in the Red Sea, The Great Barrier Reef and as far north as southern Japan.

Tridacna clams possess a shell made of calcium carbonate to protect themselves from predation. Each species has slight variations in shell size, shape, and scutes (scales). However all Tridacna clams possess an inlet siphon utilized to transport food and oxygen into the clam and an exhalent siphon utilized to export waste, sperm and eggs from the clam. Tridacna clams also possess various internal organs such as a kidney, gills, heart, stomach, gonads and various muscles to control the opening and closing of its shell. These clams also possess a byssal gland (the foot) which produces fiber like threads to anchor the clam into place. The most noticeable part of the Tridacna clam is the fleshy colorful mantle which extends over the entire shell. A symbiotic algae known as zooxanthellae lives within the tissue of the clam producing various products of photosynthesis during the day such as organic carbon, nitrogen, oxygen, glucose, amino acids and other essential materials. In return the algae lives within the protection of its host and feeds off the nutrients and carbon dioxide produced by the host.

Care for Tridacna clams is relatively consistent from species to species with slight variations in a preferable placement within the reef. As stated earlier Tridacna clams utilize their symbiotic algae to produce the majority of their energy requirements (estimated 75%) so proper lighting is considered a must especially since these clams possess various internal organs thus requiring a higher degree of energy to maintain these organs. The most preferable lighting for Tridacna clams would be high quality LEDs or Metal halides as these lighting systems provide proper lighting to high demand photosynthetic organisms. T-5s and compact fluorescents can be utilized but placement of the clam should be close to the surface to maximize exposure.IMG_1378

Supplementing the missing 25% of their energy requirements is generally done by absorbing nutrients and filter feeding. These clams also do best in nutrient filled water as they constantly filter water through their bodies so an ultra-low nutrient SPS-style system may not be the best environment for Tridacna clams. The addition of various filter feeder foods such as phytoplankton, rotifers, and marine snow can prove beneficial to Tridacna clams if not necessary for very small clams under 3 inches in size. The reason for supplementing filter feeder foods for small clams is their small surface area contains little zooxanthellae and at this size/age they rely more on filtering particulates out of the water column.

Another consideration for keeping these clams is their heavy demand for calcium and alkalinity within the aquarium. As the clam grows it will deplete a large proportion of the available calcium and alkalinity within the water thus requiring an efficient dosing regimen of either two part supplements (for smaller systems) and calcium reactors (for larger systems). Kalkwasser can also be considered as a complementary method to either two part/ calcium reactors as Kalkwasser is typically dependent upon evaporation rate and CO2 concentration in order to introduce calcium and alkalinity in small proportions. Kalkwasser must be added slowly into the aquarium (drip) because of its very high pH. Water changes will also help replenish these elements. Finally flow, although some Tridacna clams such a T. maxima and T. crocea live in shallow water commonly exposed to high flow and crashing currents the flow being exposed to any clam within the aquarium should be moderate as high flow will cause the mantle to retract and increases the risk of introducing air bubbles into the clam.

When purchasing a clam look for a healthy individual which has its mantel fully extended with good coloration without any signs of bleaching. Consider performing a light test by slowly passing your hand over the clam, the clam should quickly retract its mantle indicating good health. Examine for gaping within the current siphon which should normally be a narrow, slit-like opening not a large wide oval. Ensure the byssus (the foot) is intact and undamaged. Also look for new growth on the clam which indicates good health. When moving clams avoid exposing them to air as air bubbles can potentially be trapped within the clam causing complication. Finally Tridacna clams should be acclimated to a new aquarium by utilizing the drip method which slowly acclimates the clam to new water parameters and temperatures.

 


IMG_1382

Tridacna maxima:

-The majority of maximas are found in high numbers living in depths less than 25 feet.

-These clams are found living on limestone substrates, coral rubble and living corals. So placement should be on the rock work higher up on the reef.

-Typically found in bright shades of blue they can also be found in brown, green, and black/purple.

-Maximas are similar in appearance to croceas but can be told apart by looking at their shell, maximas typically have a more elongated shell and have more pronounced scutes.

-Maximas grow to a maximum 12 inches in length.


 

Tridacna_crocea_recorte

Tridacna crocea:

-Also known as the boring clam due to their habit of secreting an acidic substance to melt a hole within a substrate. The clam will then grind back and forth until the entire body of the clam is crammed within rock work. This provides extra protection for the clam but often deforms the shell and wears down the scutes.

– Large numbers of croceas are often found in depths of less than 25 feet making them the shallowest depth of all Tridacna species.

– Croceas should be placed similar onto the rockwork higher up within the reef similar to maximas.

-Typically croceas found in various shades of blue with some individuals exhibiting purple and other colors.

-They differ from maximas by having a shorter shell with smoother scutes.

-Croceas grow to a maximum of 6inches making them the smallest of all Tridacna species.


 

Tridacna_squamosa_Maldives

Tridacna squamosa:

– Commonly known as the fluted clam due to the large scutes of the shell.

Tridacna squamosa clam is found in a variety of environments from steep walls to reef flats and in and outside of lagoons. However their typically found at depths at around 50ft. This range of environments allows Tridacna squamosa to be more adaptable to various conditions compared to T. maxima and T. crocea.

– These clams can be placed on the substrate/rockwork.

– Squamosa clams are found in a variety of colors with blue being exceptionally rare and command a high price.

– They can be easily identified by their large scutes resembling a fan and well extended mantle.

– Squamosas can grow to 16inches.


 

IMG_1381

Tridacna derasa:

Tridacna derasa is found in a wide variety of depths ranging from 10-60ft making them very adaptable to a variety of aquarium conditions. This makes derasas a great beginner clam and would be highly recommended.

-These clams prefer to be placed on the substrate

-Typically found in shades of light brown, white, and yellow coloration along with a blue rim along the edge of the mantle.

-Derasa clams a very easy to identify due to their extremely smooth shell and distinctive coloration.

-Derasa grows to 24inches, making it the largest Tridacna aquarium clam.


Interested in bringing a tridacnid home? Come on in to Absolutely Fish and we’ll help you choose the perfect one.

 



References

http://oceanservice.noaa.gov/education/kits/corals/coral02_zooxanthellae.html

http://www.advancedaquarist.com/2012/2/inverts

http://reefkeeping.com/issues/2007-10/jf/index.php

http://www.tfhmagazine.com/details/articles/giant-clam-placement-in-the-aquarium-the-reefer.htm

http://www.peteducation.com/article.cfm?c=16+1909&aid=3097

https://www.bluezooaquatics.com/resources.asp?show=419

http://www.reefkeeping.com/issues/2002-07/jf/feature/

 

 

 

 

 

 

 

Copyright 2013 Absolutely Fish, Inc. All Rights Reserved