Gizzard vs Threadfin

Dave Stewart made the comment in AndyG's post, "Fall Cold Fronts", this week concerning "Learn what affects the sad and how they react to changing conditions." For some of us, we know that bass love shad, and we all tend to follow the shad, but there are a lot of factors which can cause shad to react to changing conditions.

First, lets consider the two most commn shad in our lakes...the Threadfin (TF) and the Gizzard (Giz). The TF has a slender silver body with black spot behind the gill plate, fins have a yellow cast and their backs are in iridescent blue-green. They stay eating size all their life and have no spines to inhibit being eaten easily. The TF congregate over deep water in the day and may move to the shallows at night. They are sensitive to cool temperatures, are zooplankton eaters and live up to three years.

The Giz have a silvery blue back, silvery sides, white sides, dark fins and a dark purple dot behind the gill plate. They like stained/turbid water and occupy shallow coves more often than the TF. However, at night both species may mix. When young they are in competition with the TF for zooplankton, but when adult they become bottom feeders on algae and debris. The Giz live up to 8 years. The juveniles like quiet surface water, spawn at night in the shallows with a 6 week spawning period.

Both species start together feeding in open water on plankton and are in competition for plankton in the spring and summer. Good places to find both species are inflow areas where the oxygen levels are greater. As the Giz matures they start to feed off the bottom while the TF stay in the open water.

One disadvantage to the Giz is their rapid growth. The first year they grow to 4" while the TF max's out at 3". After the 3rd year, the Giz is out of predator range except for the striper. However, the adult Giz allows for the future spawns. Spawn times can be different for both species which allows for small shad for the longer bass feeding times after the bass spawn. However, if the "hatching times" of the shad are out of syn with the bass spawn, the bass fry may not have adequate food for growth during their early stage of growth. Giz spawn is between 50-70 degrees at night in shallow water. The TF spawn is shorty after dawn along weedy shores or in open water around wooden structures. They spawn when the water temps are between 62-82 degrees in May/June. They may also spawn in September if the plankton growth becomes ideal.

The Giz avoid thick weedbeds, but do forage along the shorelines which makes them available to bass. TF die once water temps reach 40 degrees. Giz do not. TF start seeking out warmer water in the fall when water temps are between 40-60 degrees. Warm springs and inflows are good places to find shad during this time of year. TF will also start going deeper to find contant water temps. Shad do not feed or move much below 50 degrees. Cold temps will make them school tightly in larger numbers. When the weather conditions cause temps to fluctuate drastically, shad will die and fall to the bottom. This is why the jiggomg spoon in cold weather is so effective off the bottom or the F-N-F on those cold, wintery days.

Well Shad--Thank you

Thanks for the info Bonefish. That was a good read.

This is the type of post that I come in here to read. Good information.

Thanks, Moose. I also ask Dave Stewart in AndyG's post on "Cold Fronts" about the effect Bp has on zooplankton and here's what he had to say. Zooplankton is more readily available in periods of low pressure and has a lot to do with why you get a good bite during the low pressure periods. Changes in Bp have more of an effect on the bite than light penetration. Shad also feed more on phytoplankton than anything because of its availability. Thanks, Dave, for your reply.