Do female predatory fish that feed on high lipid fish like menhaden, mackerel and herring become more fecund than those that feed on squid and crustaceans?
**Yes, female predatory fish feeding primarily on high-lipid (oily) forage fish such as menhaden, mackerel, and herring generally become more fecund** (i.e., produce more or higher-quality eggs) than those relying more on squid and crustaceans. This stems from basic fish reproductive physiology: ovaries and developing eggs (oocytes) are highly lipid-dependent. Lipids provide energy for gonad growth and essential fatty acids (especially omega-3 PUFAs like DHA and EPA) that are incorporated into egg yolk for embryo development. Prey with higher energy density and lipid content directly improve female condition, gonadosomatic index (GSI), oocyte size/number, and overall fecundity. (LINK) (LINK)
https://www.mdpi.com/2410-3888/7/5/291
https://pmc.ncbi.nlm.nih.gov/articles/PMC9973229
High-lipid forage fish (e.g., menhaden, Atlantic herring, mackerel) are energy-rich (often 20+ kJ/g dry weight or high muscle lipid percentages seasonally) and rich in PUFAs. In contrast, squid and many crustaceans have higher protein but lower lipid/energy density and different fatty-acid profiles, making them comparatively lower-quality for reproduction in many systems.
file:///C:/Users/bkind/Downloads/noaa_60969_DS1-1.pdf
https://osu-wams-blogs-uploads.s3.amazonaws.com/blogs.dir/2849/files/2017/03/Anthony_et_al_2000.pdf
### Direct Evidence from Predatory Fish
– **European perch (Perca fluviatilis, a classic predatory fish)** in the Baltic Sea: All individuals had fish-based diets, but specialists feeding more on pelagic planktivorous fish (e.g., herring or sprat — high in lipids and fatty acids) showed significantly higher gonad weights (a strong proxy for fecundity and reproductive output). Ovaries are lipid-rich, and fatty acids from such prey are directly transferred to eggs. Specialists on lower-lipid benthic/invertebrate prey (more crustacean-like) had lower reproductive investment.
– **Striped bass (Morone saxatilis, another key predator)** in systems like Chesapeake Bay: Menhaden is a primary high-lipid prey. Declines in menhaden abundance lead to poorer striped bass condition, increased disease, and reduced spawning success/population fecundity. Ecosystem reference point models explicitly link higher menhaden availability to better striped bass reproductive capacity (fecundity targets/thresholds). Predators in better condition (from lipid-rich fish prey) produce more eggs per female, as fish fecundity often scales with body size and energy reserves.
https://academic.oup.com/mcf/article/10/4/370/7827030
### Broader Support
Aquaculture and lab studies on carnivorous/predatory broodstock fish (e.g., snakehead murrel) consistently show that raising dietary lipid levels (or PUFA supplementation) significantly boosts GSI, fecundity, and egg quality — mirroring the nutritional advantage of oily fish prey over lower-lipid alternatives.
In wild marine food webs, shifts toward energy-rich fish prey (vs. squid or invertebrates) improve predator condition and reproduction across species, analogous to the “junk food hypothesis” observed in seabirds (low-lipid squid/crustacean diets reduce breeding success). No evidence shows squid or crustaceans superior for fecundity; they often support growth but yield lower reproductive output when dominant in the diet.
Fecundity can also vary with fish size, age, temperature, and population density, but diet-driven lipid intake is a major controllable factor. In summary, predators “what they eat” matters — oily fish like menhaden, mackerel, and herring fuel higher reproductive success than squid/crustacean-heavy diets. This principle underpins forage-fish management (e.g., protecting menhaden stocks for predators).