| No | Arguments | Refutations |
| 6.1 | Old/large adult fish stop growing because all their energy goes to reproduction (70–77) | Well-fed, non-reproducing fish (e.g., in aquaria) stop growing at some point. In addition, the females of >80% of fish species grow to be larger than the males (see www.fishbase.org and section on “Fish growth vs. reproduction”). |
| 6.2 | “Pauly’s assumption that female fish have higher reproductive output than male fish is unsupported by data. There is no pattern of female fish investing more in reproduction than males in fish (or other water-breathing ectotherm Parker et al. (85). Indeed, for the species given by Pauly (84), females invest relatively less in reproduction than males as a proportion of body mass (see figure 5.5 in Sarre’s doctoral dissertation (173)” (83). Note that “figure 5.5” is a plot of ova stages versus body weight in female (only) black bream (Acanthopagrus butcheri), which does not deal with the female-to-male comparison at hand; it is likely that the authors meant figure 5.6, which compare the gonosomatic index (GSI) of females and male black breams. In addition, in a context similar to that above, an author (174) proposed the ad hoc hypothesis that the greater reproductive investment of the female is more apparent than real, i.e., “[t]he male gonad often weighs less than the female gonad. This does not mean smaller spawning loss in males because sperm, consisting almost entirely of DNA, RNA and lipoids, is likely to be the most expensive substance in the fish body.” | A review of 168 mammal, 97 bird, 3 reptile, 100 amphibian, 98 fish, and 16 invertebrate species (175) concluded that, overall, the cost of reproduction, in female was up to three orders of magnitude higher than for males. This confirms Gould (176), who wrote “[s]perm is small and cheap, easily manufactured in large quantities by little creatures. A sperm cell is little more than a nucleus of naked DNA with a delivery system. Eggs, on the other hand, must be large, for they provide the cytoplasm (all the rest of the cell) with mitochondria […]), and all other parts that a zygote needs to begin the process of embryonic growth….” Parker et al. (85) state in their abstract, that sessile invertebrates (not “fish”) are “subject mainly to selection on gamete production and gamete success and so high gonad expenditure is expected in both sexes. […]When GSI is asymmetric, female GSI usually exceeds male GSI, as least in echinoderms. […] Intriguingly, higher male GSI also occur in some species […] of gastropod molluscs”. If these authors had found that male GSI routinely matches that of females, they would not have used the word ‘intriguingly’. They also note that their “limited data also suggest that higher male GSI may be the prevalent pattern in sperm casters (where only males release gametes).” As for figure 5.6 in Sarre’s unpublished thesis, it shows male GSI to be occasionally higher than female GSI, but GSI is an index relating gonad weight a given time to the weight of the body, not the rate of production of gonad tissue, which alone relates to reproductive costs. |
| 6.3 | A critique (166) of (7) included “the bioenergetic model assumes that the term scaling directly with weight is due to catabolism, but the there is a strong case that reproductive investment is the principal factor (75, 177, 178).” | The answer to this (7) was that “Brander et al. argue that fish growth is inversely proportional to reproductive investment. However, this […] cannot explain why female fish (which have a much larger reproductive investment than male fish) reach larger sizes than male in the majority of fish species, and why sterile fish […] grow asymptotically. Moreover […] diploid (reproductively active) and triploid (sterile) fish show very similar growth patterns despite large differences in reproductive investment (80).” |