Tuesday, January 29, 2013

You can learn a lot from a bass, by Don Orth

It is the start of the spring semester and there are 21 Ichthyology students enrolled as we start at the very beginning,  learning about the earliest and simplest fish and dissecting the lamprey.    One of the oldest fish fossils is Arandaspis prionotolepis, an extinct jawless fish that lived in the Ordovician period, about 470 to 480 million years ago.    However, as I read the student responses to the syllabus from the first day of class I realize that students want to know about more about me, my favorite fish, and my earliest experiences with fish.    I am surprised.  

The first fishes I ever caught were a chub, most likely a horneyhead chub Nocomis biguttatus, captured on a piece of a crayfish, and a sunfish caught on small piece of worm  - can’t be sure which one was first.   Over the years of studying fishes, the fish that I have encountered most frequently at the end of the line has been the smallmouth bass Micropterus dolomieu.    With Shannon Brewer I recently wrote a short summary on the species for the upcoming Black Bass Diversity: Multidisciplinary Science for Conservation Symposium.    Although I thought I knew a lot about the species I found that there are still new discoveries to be made and old ideas that re-emerge.     The smallmouth bass was first described by the French naturalist Bernard Germain de Lacépède (1756-1825) who traveled widely in the pursuit of fishes and wrote multiple volumes of Histoire naturelle des poissons.   Lacépède named the smallmouth bass after his associate, the French mineralogist M. Dolomieu.     In a mistake that would confuse countless novice Ichthyologists since then, the specimen has a damaged dorsal fin, hence the genus name would forever be  Micropterus, meaning   “small fin”.    So I am reminded that we all make mistakes but we hope they easier to learn from and to hide.     I learned a lot from the smallmouth bass and believe it is appropriate to pay homage to the fish.

So let’s start at the beginning.   The smallmouth bass is a member of the family Centrarchidae and the most recent common ancestral centrarchid was recently aged at 33.59 million years ago by Thomas Near and colleagues (Evolution 59:1768-1782) using a technique that combines fossil aging and molecular clocks.  Yes, indeed there are fossil Micropterus that were aged as 12 to 16 million years old,  which translates to 4 to 5 millions of generations producing changes that we can see today – nine distinct species of Micropterus. Smallmouth bass differ from the others black bass in having larger eggs, larger fry, and longer period of parental care.  Black bass as a group support important recreational fisheries in North America and are easily characterized as a mult-billion dollar group of fishes.  

Smallmouth bass males select a suitable nest location, clear it of loose material and create a depression,  before courting a nearby female.  Males are known for their aggressive defense of the nest site and the developing brood.   At the actual spawning, males and females show sexual dimorphism in color pattern.  Dark vertical bars against a pale background are evident in the ready female smallmouth bass.    The iris becomes distinctly red in the spawning male smallmouth bass.     I have seen no studies that investigate this further.  Why the more intense red iris?   How long does it last?  Does it have adaptive significance? Smallmouth bass may guard the developing brood for as long as 7 weeks.  Initially the male is able to keep the free-swimming larvae, or black fry, in a tight school but the larvae due disperse in search for food.  However,  at night the fry stay together and settle on the bottom until sunrise.   Parental care is the key factor influencing early survival.  Removal of a guarding male may allow egg predators to swarm the nest until the male returns.    The smallmouth bass may grow as fast as 1mm/d and soon disperse from the nest and the parental male. 
Smallmouth bass have been widely introduced because of their popularity as a recreational fish, even in areas with marginal conditions to support these fish.   Because there are an opportunistic top carnivore they often cause shifts in fish assemblages, or even elimination or redistribution of other fish and crayfish.   They have had a devastating effect on indigenous fishes in parts of South Africa and Oahu (Hawaii).  In their native range they serve as intermediate hosts for a number of flatworm parasites and hosts for native freshwater mussels, such as the wavy-rayed lampmussel Lampsilis fasciola and others   These mussels have mantle flap lures that imitate fish prey, attracting smallmouth bass, which are then infected with the glochidea.  See video of Lampsilis fasciola mantle lure by  Zac Wolf.    Fascinating!
Lampsilis fasciola mantle lure. Photo by Dick Neves