Growth
  1. The energy budget
    1. Growth is the last term in the energy budget (Fig. 5.9, Helfman et al.)
      1. C = E + R + P; food consumed is excreted, used for activity, or production
    2. Measuring terms
      1. Respiration: usually measured as consumption of oxygen in fishes, standard conversion to energy
      2. Production: usually measured in biomass, conversion to energy
      3. Excretion: usually measured by difference.
      4. complete energy budgets rarely attempted
  2. How fish grow
    1. Determinate versus indeterminate growth
      1. endotherms: determinate

        2. typically little growth after maturation

      2. fishes: indeterminate (handout: fig. 5-3a, p. 74 diana)
        1. continued growth after maturation
        2. slow approach to asymptote, rarely if ever achieved
        3. stanzas: note that growth of larval stage may be v. different. In salmon, several stanzas.
    2. Endocrine control of growth
      1. adenohypophysis (glandular part of pituitary) produces growth hormone
      2. gh has many functions
      3. receptors in liver, resultant production of insulin-like growth factors (IGF)
    3. growth models
      1. commonly used growth model: von Bertalanffy (p 71 Diana)
        1. Lt = Linf [1 - e-k(t-t0)]
        2. k is growth rate, t0 is age at zero length, L infinity is asymptote
        3. ignores the initially exponential growth in larval stage
  3. Measures of growth
    1. Measures of size
      1. length
        1. Different fish of the same length may have different weights
      2. weight
        1. wet weight: usually wiped or blotted
          1. easy to take
          2. can release fish
          3. not too meaningful in some ways: water content of tissue variable
        2. dry weight
          1. relatively easy to take on a dead fish
          2. can't bring back to life
          3. Different fish of same dry weight may have different amount of energy stored: lots of fat means lots more energy
    2. measures of growth
      1. individuals over time, lab population or via tag-recapture
      2. size vs. age relationships
    3. age: hard parts analysis
      1. general idea: same as tree trunk
        1. structures growing along with the body of the fish (rather than proliferating in number)
        2. features on these structures signal growth rate
        3. growth varies seasonally, so marks are left every year.
      2. scales. (fig. 3.17 in Helfman et al., also dwarf perch scale)
        1. circuli: growth ridges form at constant rate
        2. closely spaced circuli indicate slow growth, winter
      3. otoliths
        1. variation in composition with growth rate
        2. winters, less opaque
        3. also there are daily growth increments: age in days and thus growth in days
      4. other hard parts: fig. 10.3, Helfman et al.
    4. Estimation of growth in field (handout: fig. 8.4, Moyle and Cech)
      1. with age information, can get average size at each age
      2. Static method: estimate growth as change in size between age classes in single sample
        1. benefit: single sample only
        2. drawback: ignores past variation among years in growth

          3. E.G., the 2-yr-olds this year may have grown v. little in their first year because it was cold. Static method doesn't take this into account.

        3. another drawback: selective mortality of slow-growing or fast-growing fish will influence growth estimate.
      3. cohort: take samples over time
        1. Does account for any annual variation in growth
        2. This method, like cohort method, does not account for any selective mortality
  4. (Some) factors affecting growth
    1. age, size, maturity, sex
      1. Growth decreases with age
      2. Why?
        1. increasing allocation to reproduction
        2. increasing allocation to maintenance?
      3. Growth curves often differ between sexes
        1. different age of maturity
        2. differing level allocation to reproduction
        3. other intrinsic differences
    2. ration: food intake, food availability (handout, fig. 5.4 Diana)
      1. growth will increase with ration, but at decreasing rate
      2. maintenance ration: no growth
      3. optimum ration: best conversion
      4. above this, gross growth efficiency declines
    3. temperature
      1. Temp influences a number of processes affecting growth
      2. Maintenance needs increase with temperature at accelerating rate
      3. Maximum rations increase, then fall off (handout: fig. 5-7 diana)
      4. so intermediate optimum for growth:
      5. if food is limited, lower optimum temperature
        1. extreme case, starving fish: tend to choose colder water than fed fish
    4. genetics
      1. Populations and strains known to vary in growth rate
      2. Example: the Atlantic silverside (handout).
        1. individuals from northern populations can grow faster at all temps than southern
        2. consume more food and utilize more efficiently
        3. how? Probably different levels of growth hormone
        4. why? We believe stronger selection favoring large size in northern fish