Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Tilapia

I stocked 30# of Mozambique Tilapia in my 2 acre pond on May 7. They were 1/2 pound and less.


Water temps dipped down to 50° before I found any floaters. So far I’ve only recovered 4 — two were still alive (1.34 lbs and .94 lbs) and I’ve seen a total of 6. The rest I’ve harvested have been right around a pound. I’ve got more nutrients than I need, so I’m trying to pull out as many as I can. Temps bounced back to 56° within two days and I haven’t found any more dead since
Got to watch an Osprey harvest one of them after spotting it with my drone.

Secchi visibility is just short of 7 feet so they are easy to spot. There were several ducks on the pond in the picture below. Look like white dots from 350 feet.


Cover - 6 feet deep


I have 2 questions.
Would 1 to 1.34 # be the original stockers?

From one of Mister Cody's previous posts he had some over 2#, but not sure how large they were when stocked.
What length/weight should I expect to see from the ones that hatched?

Here's a video from the drone of the one I spotted that the Osprey harvested. Wish I could have got that on video. I got a couple of pictures with my phone but they are not that good.

Click on WATCH ON YouTube to see the video.



I've got to get ahead of the bushy pond weed next year, I pulled some out earlier this week and it was full of 1/2 inch to 1 inch BG so I guess it does have some benefit.

Learnin',

I think that is really good growth considering the starting weights and that they are Moz TP. If the 1.34 lb TP weighed .5 lbs at stocking ... then it gained 382 grams over the time period (194 days) and that is right at an average of 2 grams daily. I would consider that very good growth. Different species of TP have different growth potential. Niles and Blues have greater potential. Moz TP have greater fecundity (per unit weight of females) and they reproduce at a younger ages (something that slows down the specific growth of MozTP at younger ages). The benefit of that is that it keeps offspring consumable for longer periods of time. Swingle noted that Moz TP were significantly easier to catch by hook and line than other TP species.

My larger size of tilapia stockers were 7inches and 5.1 oz(145g) on June 01. After 106 days some weighed 2.2lbs (989grams) growing 9 to 9.3 grams per day to a fish 13" long.

Very remarkable, Bill. Much better than BG. What average gain per day would you expect of BG in your climate starting the same weight and growing the same length of time?

That's fantastic growth!!

What type of TP were they?

I was guessing at the weight but the largest were about 7 inches, but thick. I will weigh some next year if I stock them. Still trying to decide if it's worth the investment. I'm guessing yours had significantly more feed or FA than mine. I use a drone to see what's feeding and have only seen TP a few times. Mine have been in 180 days plus.

I do not have daily weight measurements per day of BG for growth as outdoor growth for an entire year due to winter conditions in Ohio where my fish growing days are around 180 with water temperature 60F+. For indoor RAS growth of BG from 1" (abt 0.15g) to 6.75 " after 273days and weighing 110g is around 0.4 gram/day for the shooters / jumpers. Then continued growth was outdoors to 1 yr old as 365 days was to 9” and 290 grams for 0.79grams/day.

I find it very interesting that weight gain per day for tilapia (primarily blue TP genetics) dramatically increased and was a lot more gain / day after the fish reached 7" long. From TP fry and growing for 151 days indoor RAS (Jan-Jun01) they likely as the largest males weighed around 135 - 145 grams. That weight gain per day was 0.96grams/day or close to 1 gram per day. Important note is that the amount of food supplied was decreased about 20-30 days proir to Jun1 to intentially slow the growth rate to produce TP primarily in the 3 fish/lb range. Thereafter the 7" at 145 grams and then growing for the next 106 days water 70F to mostly 78F to 87F the average daily weight gain was a maximum of 9.3 grams per day to some TP being 13” long and some weighing 2.0 to 2.2lbs at nine months old. Average weight gain per day for 257 total days was 3.89grams / day.

Some of the 2.2 lb TP were from a pond that had no pellet feeding and Chara as a main food source. The 2 lb TP from my pond daily ate some pellets and primarily Chara.

Your fish are well cared for Bill. Thanks for sharing your BG growth as well.

I wanted to answer the second question particularly but at the time you posted I had not yet developed a climate model for Moz TP. Finally got around to spending time with it this past week. Two papers contributed to the model they can be found here:

https://www.researchgate.net/public...ation_in_tilapia_oreochromis_mossambicus

https://seafwa.org/journal/1957/further-experiments-tilapia-mossambica-pondfish

The first established growth at 82.5F .... while the second served as a reference for temperature dependent growth.

It is important to understand that after the onset of sexual maturity ... that the gain of males is about double the gain of females. In your initial stocking, the small fish were females from last year's crop while the larger fish were males. It is also important to understand that fish of low relative weight have greater potential to gain weight. So if one of the males was longer but weighed no more than short males which were of higher relative weight ... he would substantially outgrow peers when placed in an environment where food supply was not limited. So TP are often overwintered under conditions of high density and where slow growth is desired on limited ration. This favors smaller fish because each fish has just one mouth and they can get by or grow on rations smaller than the larger fish. This results in shorter fish being of higher RW than longer fish. Anyways, it is likely that the longer of your fish were of lower RW than the shorter ones. Males that were above the average length of males and of the lowest RW had the most potential for growth (in average grams/day).

Below is a chart of male MOZ TP growth in your climate with an average start weight of .5 lbs. The model is consistent with Swingle's results and your results would be only modestly different that Swingle's. For the growout period, the climate isn't different by alot. But the model assumes 1.4 grams per day at 82.5F. The modeled growth varies throughout the grow-out but from the period from 5.7.25 to 10.26.25 the average growth is estimated at 1.29 grams per day culminating in an average weight of 1 lbs on 10.26.25. I don't go beyond that date because I estimate the growth to be nil after that date due to temps at 60F and below. Assuming females averaged 1/4 lbs at initial stocking ... I estimate that they ... on average ... attained a weight of 1/2 lb on 10.26.25.

Now for the offspring. I estimate that the temps required for successful reproduction initiated around 5/15/25. It's not clear when that temp actually occurred but using that date as the fertilization date and 5/19/25 as the hatch date I estimate that male offspring of that first cohort reached an average weight of 141 grams (~0.37 lbs) by 10.26.25. The females would have been smaller averaging 82 grams (~0.18 lbs) on the same date.



It's not good to judge your observed growth with another species of TP. The appropriate yardstick is how well your Moz TP grew ... climate adjusted ... relative to their average potential for growth. Based on experiences of the two studies above ... the growth is a very high proportion of what their potential is. They grew well indeed. The 1.34 lb Moz TP, IMO, is not what a 1/2 lb Moz TP should be expected to grow to in your climate. Rather it represents an exception that may have had greater individual genetic potential or may have been longer than peers of similar weight at the time of stocking

FWIW, there are no pure strain T-Moz out there....all are hybridized now. I seriously question and doubt the weight gain data, or view it as very misleading, at best. Lost growth in fish, including Tilapia, is forever lost and can't be reclaimed. A fish with a high Wr, and in an environment of unlimited food supply will always outpace a larger fish of low Wr, in growth percentage relative to length. A larger fish, with a larger mouth can simply eat more volume than a smaller fish, so the larger fish would always gain more total weight, yet will yield a lower percentage of meat....Like I say, the data, at best, is misleading. Also, it is not uncommon for 1/4-12 pound stockers to gain 2+ pounds in a single growing season in a pond. Females only gain less because they eat less while brooding eggs/fry, and energy diverted into growing eggs. I also don't know where you got your info claiming T-Moz are more fecund than a T-Aurea. Average egg production is the same. The Blue (T-Aurea) becomes sexually mature about 2 weeks later than the 12 weeks of T-Moz, and T-Nilotica much later. The T-Aurea however, has a lower temperature range for laying eggs than the T-Moz, so is actually the most fecund of species stocked in sportfish ponds, and early off spring will also be laying eggs, longer....Info and conclusions on Tilapia matters a lot whether the fish are in a sportfish, or food production setting, as management is almost the exact opposite for each setting....ie what is great for food production, is horrible when used in a sportfish pond

BTW, the one tail that displays fin ray patterns are that the Tilapia are primarily Blues (T-Aurea) Not T-Moz. T-Moz have ray patterns similar to lines extending away from the body, outward to the caudal fin tips.....The pattern shown is radial, like curved sound waves emanating from the body in pattern arced pattern on the Caudal

So for sure ... I am not going to accuse the OP's supplier of selling blues as Moz Tilapia. I think I know who the supplier is. I figure ... even being as far north as he is that he made a choice to supply Moz TP over the other species of TP for good reasons. Just not going to venture how much ... if any ... other TP genes are in them. Anyways, I figure his choice to supply Moz TP was founded in the same reasons I would want to stock them for the purpose of forage. I think he did his research, much like I have. Google is a wonderful thing. As for whether no one has pure strains of Moz TP, I just don't know. Here in Texas, only pure strain Moz TP are allowed for stocking. Suppliers say they are selling pure strains. They do look different depending on supplier. The most beautiful? Overton's IMHO.

For anyone who believes that fish cannot regain RW when food is more plentiful, there is not much I can do to help you. We all form opinions and sometimes they get in the way of common sense and multitudes of evidence. Often these opinions when expressed in words don't make sense. When I hear/read them ... I just twist my head.

When my kids get to arguing about something ... I intervene with "Let's Google it!". We have at our disposal a virtual library. Not that one doesn't have to discriminate. Often the results have sources with economic interests to maintain. These references are far less reliable and one does have discriminate. But by and large, if one uses the library with an open yet discriminating mind he will learn a few things new. This isn't always the case ... sometimes ... people will immerse themselves only in information that will confirm their opinions. Ultimately, it's everyone's individual responsibility to be conscientious about what opinions he forms.

To that end, I'd recommend to anyone to do your own due diligence. If you don't believe that Blues and Niles grow faster than Moz TP ... just do your own research. There is lots of evidence out there. You will form a better opinion than making a choice among posts here. Use Google, satisfy yourself that the OPs Moz. TP should be growing as fast as Bill's Blues or Niles (which ever they might be). Really, that goes for everything. That little signature at the base of my posts? It's not there for other's benefit (even though everyone would be well served to be mindful of it). That little epithet is a reminder to me to be careful of what I post.

Anyways, I stand by what I posted. I take the OP's report that the species of TP is Moz TP at face value. When compared to studies on growth, (swingle's being one of sportfish application at stocking rates no higher than many initial stock of BG), the OP's growth falls not far from the tree. I don't think he needs to feel bad about the growth. They performed as I would expect Moz. TP to perform in his neck of the woods. If something walks like a duck, quacks like a duck, and swims like a duck ... maybe it is a duck. Likewise, if the OPs TP grew like MozTP, maybe just maybe, they are MozTP which the OP reported and his supplier claims they are.

If they weren't big enough, then he could seek a different species. Maybe a good place to start is where Bill sourced his fish. But frankly, I don't think his TP situation is broken. I personally prefer Moz. TP for forage because they grow slower and reach sexual maturity at younger ages and smaller sizes. They are consumable for longer periods of time ... and that is a good thing. Swingle reported they are significantly easier to catch than Niles. How they compare to blues? I don't know but I can tell you that I have caught blues and when one is in them, they didn't seem all that difficult to catch to me. Do blues give you more fecundity than Moz TP? It depends on how you look at it. A blue of greater weight can certainly have more eggs than a MozTP of lower weight. Generally, fecundity is enumerated as a range of egg numbers per unit weight of female fish. So if you stock the same weight of females, MozTP will have more eggs (according to sources I find reliable) ... at least at the time of stocking. Does the temperature at the onset breeding make a big difference? Of course not. Temperatures change in most ponds too fast to afford a time span long enough to get an extra spawn in. Now in Florida, perhaps where temps are more moderately changing. But in OH, MO, or OK, no. Doesn't seem reasonable to me because the expanse of time is insufficient to get an extra spawn in... I dissent.